diff --git a/packages/app-bundle/manifest.json b/packages/app-bundle/manifest.json
index 1059261f..b02b5e69 100644
--- a/packages/app-bundle/manifest.json
+++ b/packages/app-bundle/manifest.json
@@ -950,11 +950,11 @@
     "packages/core/schema.json": "79ef4e2f0dd8103ac7a4b6ff3ddb0fd10764655f1dc678c1c401dfc43be9a1aa",
     "packages/session-ui/bunfig.toml": "82585987c8258caf58d07c6aaf4e49b7338e4da16f97c785af398aace9e6e722",
     "packages/session-ui/happydom.ts": "d81d6b14e988f058fa502c841df34b55307c57fc94a26fb4f8a5deb6aa0d4834",
-    "packages/session-ui/package.json": "1c69e65b039e6262ce50defb798233e5db99aeca4b0fe66885f7e35c2433b685",
+    "packages/session-ui/package.json": "f1edc72de0e5aa3a1b045be1c825ca359dafc8bd9cbb89208a21c53226a37d40",
     "packages/ui/package.json": "b1d168d0371e9094faae1107fc6c00be197f09bc69daa2247a3890d607f4b629",
     "packages/app/public/amico.svg": "a14b9d543d895bcdf0758f7b9ef5908ee0acaac794446494af059b159247db8f",
     "packages/app/public/oc-theme-preload.js": "27227e802b3494e7c545da903e679efdb30ccc754cd4eb5cdf08005a40d560b6",
-    "packages/app/src/app.tsx": "a72e7cef35d5de80980fbb1fc26c14d8551d1677821e72798c624842927b55fd",
+    "packages/app/src/app.tsx": "98f367769ed22ed33cbb8ff6067b3b5fc829acef1fad62b791cfd286ed9aec54",
     "packages/app/src/design-polish.css": "42cc6efaefe9a71dedd12fcb0bf2549453d9a46097cb025cf087064b29d3ccce",
     "packages/app/src/entry.tsx": "f35e1017f4c9d478d254b2a38043e5750064b6bef25169c3e07ae9f72ff1049c",
     "packages/app/src/index.css": "08179e06ce2d419a2d98acc96025f91c7709062ea9f3ad245e88dc35e75ff9f7",
@@ -1408,7 +1408,7 @@
     "packages/app/src/components/session/session-context-tab.tsx": "227243b178b517f067d9ae0ae0eec3c559beeb6681828158b0600a17e98e7f81",
     "packages/app/src/components/session/session-header.tsx": "a46591ed1097d0fdcff61fb0c5529396955e8857cbef748747c51e472d5564c5",
     "packages/app/src/components/session/session-new-view.tsx": "9510a4f550a3f0d4791e98e8025666f09d70a60fb66f193e48ee61feddae5a57",
-    "packages/app/src/components/session/session-preview-tab.tsx": "b6b4b8fe6f751499e0d3005e1f12224351df4f28f221bba10fc2f91c0f09e777",
+    "packages/app/src/components/session/session-preview-tab.tsx": "103d531614d0f904b7bb255d484ff681aaad5b66aafea308e2774c661f57bb1a",
     "packages/app/src/components/session/session-sortable-terminal-tab-v2.tsx": "08db0e378c3e07d243121f40c77e153bafe897e5e2ececd48a3e00786793032b",
     "packages/app/src/components/session/use-context-warning.ts": "af7a6d0159a5541aa02ad4d08fd694af1cc4853fc1c0a70763bc264a634d1c53",
     "packages/app/src/components/settings-v2/data-storage-controller.ts": "fa5d143cc101f3a3b9d5ad445edddc981e0d02783021d52dbfed6c8d8bf62498",
@@ -1473,7 +1473,7 @@
     "packages/session-ui/src/v2/components/basic-tool-v2.css": "55d3aa179704deddda7149342a951229ff5561127f786dd551e5df9aea8a7835",
     "packages/session-ui/src/v2/components/basic-tool-v2.tsx": "ece46d761f7d51a7a0925b3df00a5c289d891e9a514ee721016eb723d87fb406",
     "packages/session-ui/src/v2/components/diff-gutter-extension.ts": "aed07587c0c9a5f110f9ea91aa42679d6f9f66b2ec4de9043d6e2233a375acb8",
-    "packages/session-ui/src/v2/components/editable-diff-view-core.ts": "d6508b56ab48b956b8e5a66319323d17241a783bc9a73d869afbedc20159ad97",
+    "packages/session-ui/src/v2/components/editable-diff-view-core.ts": "0c05afeceeb92220b12ffde55b4887be97c6ff61931344bd8eaad0872ac32910",
     "packages/session-ui/src/v2/components/editable-diff-view.tsx": "4c0ee2525b94b04b1e708a5cacab6d3eed29ca30644321986e429b2f912b730b",
     "packages/session-ui/src/v2/components/file-name-picker.test.tsx": "1ce9741e315b549165d390c74b5885a43580aa70e24de987f9ba8388cd521b41",
     "packages/session-ui/src/v2/components/session-review-file-preview-v2.tsx": "4f1fdc944b0d422689176d04cb3580f628578915f97ea8d78594dfb9ac217146",
diff --git a/packages/app-bundle/overlay/packages/app/src/app.tsx b/packages/app-bundle/overlay/packages/app/src/app.tsx
index 19128cf8..d8728421 100644
--- a/packages/app-bundle/overlay/packages/app/src/app.tsx
+++ b/packages/app-bundle/overlay/packages/app/src/app.tsx
@@ -2,6 +2,7 @@ import "@/index.css"
 import * as Sentry from "@sentry/solid"
 import { requestComputeConnect } from "@/components/amicode-defaults-capsule"
 import { adoptWorkspaceProjects, workspaceProjects } from "@/utils/amicode-workspace-projects"
+import { adoptPreviewFileTree } from "@/utils/amicode-preview-file-tree"
 import { I18nProvider } from "@opencode-ai/ui/context"
 import { DialogProvider } from "@opencode-ai/ui/context/dialog"
 import { FileComponentProvider } from "@opencode-ai/ui/context/file"
@@ -446,6 +447,16 @@ function AmicodeThemeBridge() {
       adoptWorkspaceProjects((d as { projects?: unknown[] }).projects as Parameters<typeof adoptWorkspaceProjects>[0])
       return
     }
+    // amicode#725: preview file tree push from the extension host.
+    if (d.kind === "preview-file-tree") {
+      const msg = d as { files?: string[]; projectRoot?: string; environment?: unknown }
+      adoptPreviewFileTree(
+        (msg.files ?? []) as string[],
+        (msg.projectRoot ?? "") as string,
+        msg.environment as Parameters<typeof adoptPreviewFileTree>[2],
+      )
+      return
+    }
     if (d.kind !== "theme") return
     if (d.colorScheme === "light" || d.colorScheme === "dark") theme.setColorScheme(d.colorScheme)
   }
diff --git a/packages/app-bundle/overlay/packages/app/src/components/pdf-viewer.tsx b/packages/app-bundle/overlay/packages/app/src/components/pdf-viewer.tsx
new file mode 100644
index 00000000..b70e3a4d
--- /dev/null
+++ b/packages/app-bundle/overlay/packages/app/src/components/pdf-viewer.tsx
@@ -0,0 +1,204 @@
+// pdf-viewer.tsx — PDF rendering for the Preview tab (#727).
+// Uses pdfjs-dist to render PDF pages to canvas in a scrollable container.
+// Zoom controls, scroll position preservation across reloads, and
+// device-pixel-ratio-aware rendering.
+
+import { createEffect, createSignal, For, on, onCleanup, Show } from "solid-js"
+import { Icon } from "@opencode-ai/ui/icon"
+import * as pdfjsLib from "pdfjs-dist"
+
+// ── Worker setup ────────────────────────────────────────────────────────────
+// The pdfjs worker handles the heavy PDF parsing off the main thread.
+// Vite's ?url suffix gives us the asset URL without inlining.
+import pdfjsWorkerUrl from "pdfjs-dist/build/pdf.worker.min.mjs?url"
+
+pdfjsLib.GlobalWorkerOptions.workerSrc = pdfjsWorkerUrl
+
+// ── Types ───────────────────────────────────────────────────────────────────
+
+interface PageState {
+  pageNum: number
+  rendered: boolean
+}
+
+// ── Component ───────────────────────────────────────────────────────────────
+
+export function PDFViewer(props: {
+  /** Binary content as base64 string, or a file URL. */
+  data: string | null
+  /** Whether data is base64-encoded binary. */
+  isBase64?: boolean
+  /** Current zoom level (100 = 100%). */
+  zoom: number
+}) {
+  const [pages, setPages] = createSignal<PageState[]>([])
+  const [loading, setLoading] = createSignal(true)
+  const [error, setError] = createSignal(false)
+  const [pdfDoc, setPdfDoc] = createSignal<pdfjsLib.PDFDocumentProxy | null>(null)
+
+  let containerRef: HTMLDivElement | undefined
+  let scrollTop = 0
+  let activeLoadingTask: pdfjsLib.PDFDocumentLoadingTask | null = null
+
+  // Track scroll position for preservation across reloads
+  const saveScroll = () => {
+    if (containerRef) scrollTop = containerRef.scrollTop
+  }
+
+  // ── Load PDF ────────────────────────────────────────────────────────────
+
+  createEffect(
+    on(
+      () => props.data,
+      async (data) => {
+        if (!data) {
+          setLoading(false)
+          setError(true)
+          return
+        }
+
+        setLoading(true)
+        setError(false)
+
+        try {
+          saveScroll()
+
+          // Clean up previous loading task
+          if (activeLoadingTask) {
+            activeLoadingTask.destroy()
+            activeLoadingTask = null
+          }
+          setPdfDoc(null)
+
+          // Load PDF from base64 or URL
+          let loadingTask: pdfjsLib.PDFDocumentLoadingTask
+          if (props.isBase64) {
+            const binaryStr = atob(data)
+            const bytes = new Uint8Array(binaryStr.length)
+            for (let i = 0; i < binaryStr.length; i++) {
+              bytes[i] = binaryStr.charCodeAt(i)
+            }
+            loadingTask = pdfjsLib.getDocument({ data: bytes })
+          } else {
+            loadingTask = pdfjsLib.getDocument({ url: data })
+          }
+          activeLoadingTask = loadingTask
+
+          const doc = await loadingTask.promise
+          setPdfDoc(doc)
+
+          const pageStates: PageState[] = []
+          for (let i = 1; i <= doc.numPages; i++) {
+            pageStates.push({ pageNum: i, rendered: false })
+          }
+          setPages(pageStates)
+
+          // Restore scroll position after render
+          requestAnimationFrame(() => {
+            if (containerRef) containerRef.scrollTop = scrollTop
+          })
+        } catch {
+          setError(true)
+        } finally {
+          setLoading(false)
+        }
+      },
+    ),
+  )
+
+  onCleanup(() => {
+    if (activeLoadingTask) {
+      activeLoadingTask.destroy()
+      activeLoadingTask = null
+    }
+  })
+
+  // ── Render ──────────────────────────────────────────────────────────────
+
+  return (
+    <div class="h-full flex flex-col overflow-hidden">
+      <Show when={loading()}>
+        <div class="p-4 text-12-regular text-text-weak">Loading PDF...</div>
+      </Show>
+      <Show when={error()}>
+        <div class="h-full flex items-center justify-center text-12-regular text-text-weak p-4">
+          <div class="text-center">
+            <Icon name="circle-x" size="large" class="mx-auto mb-2 text-text-faint" />
+            <p>Could not load PDF</p>
+          </div>
+        </div>
+      </Show>
+      <Show when={!loading() && !error()}>
+        <div ref={(el) => (containerRef = el)} class="flex-1 min-h-0 overflow-auto" onScroll={saveScroll}>
+          <div class="flex flex-col items-center gap-2 py-4">
+            <For each={pages()}>
+              {(page) => (
+                <PDFPage
+                  doc={pdfDoc()!}
+                  pageNum={page.pageNum}
+                  zoom={props.zoom}
+                />
+              )}
+            </For>
+          </div>
+        </div>
+      </Show>
+    </div>
+  )
+}
+
+// ── Single page renderer ────────────────────────────────────────────────────
+
+function PDFPage(props: {
+  doc: pdfjsLib.PDFDocumentProxy
+  pageNum: number
+  zoom: number
+}) {
+  let canvasRef: HTMLCanvasElement | undefined
+  const [pageError, setPageError] = createSignal(false)
+
+  createEffect(
+    on(
+      () => [props.doc, props.pageNum, props.zoom] as const,
+      async ([doc, num, zoom]) => {
+        if (!canvasRef || !doc) return
+        setPageError(false)
+
+        try {
+          const page = await doc.getPage(num)
+          const scale = (zoom / 100) * (window.devicePixelRatio || 1)
+          const viewport = page.getViewport({ scale })
+
+          canvasRef.width = viewport.width
+          canvasRef.height = viewport.height
+          canvasRef.style.width = `${viewport.width / (window.devicePixelRatio || 1)}px`
+          canvasRef.style.height = `${viewport.height / (window.devicePixelRatio || 1)}px`
+
+          const ctx = canvasRef.getContext("2d")
+          if (!ctx) return
+
+          await page.render({ canvasContext: ctx, canvas: canvasRef, viewport }).promise
+        } catch {
+          setPageError(true)
+        }
+      },
+    ),
+  )
+
+  return (
+    <Show
+      when={!pageError()}
+      fallback={
+        <div class="p-4 text-12-regular text-text-weak">
+          Could not render page {props.pageNum}
+        </div>
+      }
+    >
+      <canvas
+        ref={(el) => (canvasRef = el)}
+        class="shadow-sm border border-border-weaker-base"
+        data-page={props.pageNum}
+      />
+    </Show>
+  )
+}
diff --git a/packages/app-bundle/overlay/packages/app/src/components/session/preview-content-area.tsx b/packages/app-bundle/overlay/packages/app/src/components/session/preview-content-area.tsx
new file mode 100644
index 00000000..d7c9ae8a
--- /dev/null
+++ b/packages/app-bundle/overlay/packages/app/src/components/session/preview-content-area.tsx
@@ -0,0 +1,279 @@
+// preview-content-area.tsx — Content area for the Preview tab (#726).
+// Routes files to type-appropriate renderers based on renderer kind.
+
+import { createEffect, createMemo, createSignal, Match, on, onCleanup, Show, Switch } from "solid-js"
+import { Markdown } from "@opencode-ai/session-ui/markdown"
+import { PlainEditor } from "@opencode-ai/session-ui/v2/plain-editor"
+import { Icon } from "@opencode-ai/ui/icon"
+import { IconButton } from "@opencode-ai/ui/icon-button"
+import { TooltipV2 } from "@opencode-ai/ui/v2/tooltip-v2"
+import { SegmentedControlV2, SegmentedControlItemV2 } from "@opencode-ai/ui/v2/segmented-control-v2"
+import { preprocessMarkdown } from "@/utils/preview-markdown"
+import {
+  rendererForExtension,
+  toolbarForRenderer,
+  extFromPath,
+  isReadOnly,
+  type RendererKind,
+} from "@/utils/renderer-dispatch"
+import { PDFViewer } from "@/components/pdf-viewer"
+import { useSDK } from "@/context/sdk"
+import { useServerSDK } from "@/context/server-sdk"
+
+// ─── Types ──────────────────────────────────────────────────────────────────
+
+type ContentMode = "preview" | "editor"
+
+// ─── Main Component ─────────────────────────────────────────────────────────
+
+export function PreviewContentArea(props: {
+  filePath: string
+  onBack: () => void
+}) {
+  const sdk = useSDK()
+  const serverSDK = useServerSDK()
+
+  const ext = createMemo(() => extFromPath(props.filePath))
+  const kind = createMemo((): RendererKind => rendererForExtension(ext()))
+  const toolbar = createMemo(() => toolbarForRenderer(kind(), false /* TODO: wire texAvailable from #729 */))
+  const readOnly = createMemo(() => isReadOnly(ext()))
+
+  const [content, setContent] = createSignal<string>("")
+  const [isBinary, setIsBinary] = createSignal(false)
+  const [loading, setLoading] = createSignal(false)
+  const [error, setError] = createSignal(false)
+  const [mode, setMode] = createSignal<ContentMode>("preview")
+  const [zoom, setZoom] = createSignal(100)
+
+  const zoomIn = () => setZoom((z) => Math.min(z + 10, 200))
+  const zoomOut = () => setZoom((z) => Math.max(z - 10, 50))
+
+  // ─── File content loading ───────────────────────────────────────────────
+
+  createEffect(
+    on(
+      () => props.filePath,
+      (path) => {
+        if (!path) return
+        setLoading(true)
+        setError(false)
+        setIsBinary(false)
+
+        sdk()
+          .client.file.read({ path })
+          .then((result) => {
+            const data = result.data
+            if (data && data.type === "text") {
+              setContent(data.content)
+              setIsBinary(false)
+            } else if (data && data.type === "binary") {
+              // Binary files (images, PDFs) — store the base64 data
+              setContent(data.content)
+              setIsBinary(true)
+            } else {
+              setContent("")
+            }
+          })
+          .catch(() => {
+            setError(true)
+            setContent("")
+          })
+          .finally(() => {
+            setLoading(false)
+          })
+      },
+    ),
+  )
+
+  // ─── Save logic (editor mode) ──────────────────────────────────────────
+
+  let saveTimer: ReturnType<typeof setTimeout> | undefined
+  const [saveStatus, setSaveStatus] = createSignal<"idle" | "saving" | "saved">("idle")
+  let savedTimer: ReturnType<typeof setTimeout> | undefined
+
+  const saveFile = (path: string, newContent: string) => {
+    const baseUrl = serverSDK().url
+    if (!baseUrl) return
+
+    setSaveStatus("saving")
+
+    fetch(new URL("/file/write", baseUrl), {
+      method: "POST",
+      headers: { "Content-Type": "application/json" },
+      body: JSON.stringify({ path, content: newContent }),
+    })
+      .then(() => {
+        setSaveStatus("saved")
+        if (savedTimer) clearTimeout(savedTimer)
+        savedTimer = setTimeout(() => setSaveStatus("idle"), 2000)
+      })
+      .catch(() => {
+        setSaveStatus("idle")
+      })
+  }
+
+  const handleEdit = (newContent: string) => {
+    setContent(newContent)
+    if (saveTimer) clearTimeout(saveTimer)
+    saveTimer = setTimeout(() => saveFile(props.filePath, newContent), 1000)
+  }
+
+  const handleImmediateSave = () => {
+    if (saveTimer) clearTimeout(saveTimer)
+    saveFile(props.filePath, content())
+  }
+
+  onCleanup(() => {
+    if (saveTimer) clearTimeout(saveTimer)
+    if (savedTimer) clearTimeout(savedTimer)
+  })
+
+  // ─── Helpers ────────────────────────────────────────────────────────────
+
+  const basename = () => {
+    const parts = props.filePath.split("/")
+    return parts[parts.length - 1] ?? props.filePath
+  }
+
+  // ─── Render ─────────────────────────────────────────────────────────────
+
+  return (
+    <div class="h-full flex flex-col overflow-hidden">
+      {/* Toolbar */}
+      <div class="shrink-0 flex items-center gap-2 px-3 py-2 border-b border-border-weaker-base">
+        <IconButton icon="arrow-left" variant="ghost" class="h-6 w-6" onClick={props.onBack} aria-label="Back to file list" />
+        <div class="flex-1 min-w-0 text-12-regular text-text-base truncate">{basename()}</div>
+
+        {/* Save status (editor kind) */}
+        <Show when={toolbar().save && saveStatus() !== "idle"}>
+          <span
+            class="text-11-medium"
+            classList={{
+              "text-green-500": saveStatus() === "saved",
+              "text-text-weak": saveStatus() === "saving",
+            }}
+          >
+            {saveStatus() === "saving" ? "Saving..." : "Saved"}
+          </span>
+        </Show>
+
+        {/* Zoom control (pdf/image/markdown) */}
+        <Show when={toolbar().zoom}>
+          <div class="shrink-0 flex items-center h-7 rounded-md border border-border-base overflow-hidden">
+            <input
+              type="text"
+              class="w-11 h-full text-center text-12-regular text-text-base bg-transparent outline-none"
+              value={`${zoom()}%`}
+              onInput={(e) => {
+                const val = parseInt(e.currentTarget.value)
+                if (!isNaN(val) && val >= 50 && val <= 200) setZoom(val)
+              }}
+              onBlur={(e) => {
+                e.currentTarget.value = `${zoom()}%`
+              }}
+              onKeyDown={(e) => {
+                if (e.key === "Enter") e.currentTarget.blur()
+              }}
+            />
+            <div class="flex items-center border-l border-border-base">
+              <button
+                class="flex items-center justify-center w-5 h-full text-text-weak hover:text-text-base hover:bg-background-stronger transition-colors"
+                onClick={zoomOut}
+                aria-label="Zoom out"
+              >
+                <span class="text-12-medium leading-none">−</span>
+              </button>
+              <button
+                class="flex items-center justify-center w-5 h-full text-text-weak hover:text-text-base hover:bg-background-stronger transition-colors -ml-0.5"
+                onClick={zoomIn}
+                aria-label="Zoom in"
+              >
+                <span class="text-12-medium leading-none">+</span>
+              </button>
+            </div>
+          </div>
+        </Show>
+
+        {/* Build button (TeX, when available — wired by slice 5) */}
+        <Show when={toolbar().build}>
+          <TooltipV2 openDelay={400} value="Build TeX">
+            <IconButton icon="activity" variant="ghost" class="h-6 w-6" aria-label="Build TeX" />
+          </TooltipV2>
+        </Show>
+
+        {/* Mode toggle (markdown: preview ↔ editor) */}
+        <Show when={toolbar().modeToggle === "preview-editor"}>
+          <SegmentedControlV2
+            value={mode()}
+            onChange={(value) => {
+              if (value === "preview" || value === "editor") setMode(value)
+            }}
+            class="!w-auto"
+            aria-label="View mode"
+          >
+            <TooltipV2 openDelay={400} value="Preview">
+              <SegmentedControlItemV2 value="preview" aria-label="Preview" class="!flex-none !px-2">
+                <Icon name="eye" size="small" />
+              </SegmentedControlItemV2>
+            </TooltipV2>
+            <TooltipV2 openDelay={400} value="Editor">
+              <SegmentedControlItemV2 value="editor" aria-label="Editor" class="!flex-none !px-2">
+                <Icon name="edit" size="small" />
+              </SegmentedControlItemV2>
+            </TooltipV2>
+          </SegmentedControlV2>
+        </Show>
+      </div>
+
+      {/* Content area */}
+      <div class="flex-1 min-h-0 overflow-auto">
+        <Show when={!loading()} fallback={<div class="p-4 text-12-regular text-text-weak">Loading...</div>}>
+          <Show when={!error()} fallback={<ErrorState />}>
+            <Switch fallback={<PlainEditor content={content()} language={ext().replace(/^\./, "")} readOnly={readOnly()} onChange={handleEdit} onSave={handleImmediateSave} />}>
+              <Match when={kind() === "markdown" && mode() === "preview"}>
+                <div
+                  class="p-4 origin-top-left [&_.katex-display]:overflow-x-auto [&_.katex-display]:overflow-y-hidden [&_.katex-display]:max-w-full [&_.katex]:text-[0.9em]"
+                  style={{ transform: `scale(${zoom() / 100})`, width: `${10000 / zoom()}%` }}
+                >
+                  <Markdown text={preprocessMarkdown(content())} class="text-12-regular" />
+                </div>
+              </Match>
+              <Match when={kind() === "markdown" && mode() === "editor"}>
+                <PlainEditor content={content()} language="md" readOnly={false} onChange={handleEdit} onSave={handleImmediateSave} />
+              </Match>
+              <Match when={kind() === "pdf"}>
+                <PDFViewer data={content()} isBase64={isBinary()} zoom={zoom()} />
+              </Match>
+              <Match when={kind() === "image"}>
+                <div
+                  class="p-4 flex items-center justify-center"
+                  style={{ transform: `scale(${zoom() / 100})`, "transform-origin": "top left", width: `${10000 / zoom()}%` }}
+                >
+                  <img
+                    src={`data:image/*;base64,${content()}`}
+                    alt={basename()}
+                    class="max-w-full"
+                    style={{ "image-rendering": "auto" }}
+                  />
+                </div>
+              </Match>
+            </Switch>
+          </Show>
+        </Show>
+      </div>
+    </div>
+  )
+}
+
+// ─── Error state ────────────────────────────────────────────────────────────
+function ErrorState() {
+  return (
+    <div class="h-full flex items-center justify-center text-12-regular text-text-weak p-4">
+      <div class="text-center">
+        <Icon name="circle-x" size="large" class="mx-auto mb-2 text-text-faint" />
+        <p>Could not load file</p>
+        <p class="text-11-regular text-text-faint mt-1">The file may have been deleted or moved</p>
+      </div>
+    </div>
+  )
+}
diff --git a/packages/app-bundle/overlay/packages/app/src/components/session/session-preview-tab.tsx b/packages/app-bundle/overlay/packages/app/src/components/session/session-preview-tab.tsx
index 787df200..d090cf7a 100644
--- a/packages/app-bundle/overlay/packages/app/src/components/session/session-preview-tab.tsx
+++ b/packages/app-bundle/overlay/packages/app/src/components/session/session-preview-tab.tsx
@@ -7,8 +7,18 @@ import { MenuV2 } from "@opencode-ai/ui/v2/menu-v2"
 import { TooltipV2 } from "@opencode-ai/ui/v2/tooltip-v2"
 import { SegmentedControlV2, SegmentedControlItemV2 } from "@opencode-ai/ui/v2/segmented-control-v2"
 import { writeClipboardViaBridge } from "@/components/prompt-input/clipboard-bridge"
+import FileTreeV2 from "@/components/file-tree-v2"
+import {
+  previewFileTree,
+  previewProjectRoot,
+  previewEnv,
+  requestPreviewFileTreeRefresh,
+} from "@/utils/amicode-preview-file-tree"
+import { preprocessMarkdown } from "@/utils/preview-markdown"
+import { PreviewContentArea } from "@/components/session/preview-content-area"
 import { useSDK } from "@/context/sdk"
 import { useServerSDK } from "@/context/server-sdk"
+import type { FileNode } from "@opencode-ai/sdk/v2"
 
 // ─── Types ──────────────────────────────────────────────────────────────────
 
@@ -26,16 +36,16 @@ interface PreviewFileState {
   unsavedContent?: string
 }
 
-// ─── Main Component ─────────────────────────────────────────────────────────
+// ─── Helpers ────────────────────────────────────────────────────────────────
 
-/**
- * Convert ```math fenced code blocks (GitHub-flavored) to $$...$$ display math
- * blocks that the Markdown component's KaTeX extension understands.
- */
-function preprocessMarkdown(text: string): string {
-  return text.replace(/```math\n([\s\S]*?)```/g, (_match, body: string) => `$$\n${body.trim()}\n$$`)
+/** Extract the filename from an absolute or relative path. */
+function basename(path: string): string {
+  const parts = path.split("/")
+  return parts[parts.length - 1] ?? path
 }
 
+// ─── Main Component ─────────────────────────────────────────────────────────
+
 export function SessionPreviewTab(props: {
   diffs: () => Array<{ file: string; status?: string }>
   touchedFiles?: () => Array<{ file: string; status: string }>
@@ -51,8 +61,12 @@ export function SessionPreviewTab(props: {
   const zoomIn = () => setZoom((z) => Math.min(z + 10, 200))
   const zoomOut = () => setZoom((z) => Math.max(z - 10, 50))
 
+  /** Whether the project-wide file tree is available (extension pushed files). */
+  const hasProjectTree = createMemo(() => previewFileTree().length > 0)
+
   // Derive the file list from touchedFiles (tool-edit history, persists regardless of git state)
   // supplemented by diffs for any files not already covered.
+  // Used as fallback when no project tree is available.
   const markdownFiles = createMemo((): PreviewFileEntry[] => {
     const seen = new Set<string>()
     const entries: PreviewFileEntry[] = []
@@ -61,65 +75,55 @@ export function SessionPreviewTab(props: {
     const touched = props.touchedFiles?.() ?? []
     const suffixToAbsolute = new Map<string, string>()
     for (const t of touched) {
-      // For "/Users/jj/.julia/dev/X", try progressively shorter suffixes
       const parts = t.file.split("/")
       for (let i = 1; i < parts.length; i++) {
         suffixToAbsolute.set(parts.slice(i).join("/"), t.file)
       }
     }
 
-    // Resolve ~/... to absolute using the suffix map
     const resolveFile = (file: string): string => {
       if (!file.startsWith("~/")) return file
-      const suffix = file.slice(2) // strip ~/
+      const suffix = file.slice(2)
       const absolute = suffixToAbsolute.get(suffix)
       return absolute ?? file
     }
 
     const toEntry = (file: string, status: string): PreviewFileEntry | null => {
       if (!file.endsWith(".md")) return null
-      // Use the resolved absolute path as the canonical key
       const resolved = resolveFile(file)
       if (seen.has(resolved)) return null
       seen.add(resolved)
       const parts = resolved.split("/")
-      const basename = parts[parts.length - 1]
-      // Show a short relative path: strip common leading segments until we hit a recognizable dir
+      const name = parts[parts.length - 1]
       const relativePath = resolved.replace(/^\/Users\/[^/]+\//, "")
       return {
         path: resolved,
         relativePath,
-        basename,
+        basename: name,
         extension: ".md" as const,
         changeType: (status === "added" ? "added" : "modified") as "added" | "modified",
       }
     }
 
-    // Primary: all files touched by edit tools in this session
     for (const t of touched) {
       const entry = toEntry(t.file, t.status)
       if (entry) entries.push(entry)
     }
-
-    // Supplement: any diff files not already in touchedFiles
     for (const d of props.diffs()) {
       const entry = toEntry(d.file, d.status === "added" ? "added" : "modified")
       if (entry) entries.push(entry)
     }
-
     return entries
   })
 
-  // Load file content when a file is selected
+  // ─── File content loading ───────────────────────────────────────────────
+
   createEffect(
     on(selectedFile, (path) => {
       if (!path) return
       setLoading(true)
 
-      // Resolve the actual filesystem path from the display path
-      const fsPath = path.startsWith("~/")
-        ? path.replace("~", process.env.HOME ?? "")
-        : path
+      const fsPath = path.startsWith("~/") ? path.replace("~", process.env.HOME ?? "") : path
 
       sdk()
         .client.file.read({ path: fsPath })
@@ -148,6 +152,22 @@ export function SessionPreviewTab(props: {
     setSelectedFile(undefined)
   }
 
+  // ─── Handle file selection from project tree ────────────────────────────
+
+  const handleProjectFileClick = (node: FileNode) => {
+    // node.path is relative; resolve to absolute using the project root
+    const root = previewProjectRoot()
+    const absPath = root ? `${root}/${node.path}` : node.path
+    setSelectedFile(absPath)
+  }
+
+  const handleEnvFileClick = (node: FileNode) => {
+    const env = previewEnv()
+    if (!env) return
+    const absPath = `${env.root}/${node.path}`
+    setSelectedFile(absPath)
+  }
+
   // ─── Raw Editor Save ────────────────────────────────────────────────────
 
   let saveTimer: ReturnType<typeof setTimeout> | undefined
@@ -155,16 +175,13 @@ export function SessionPreviewTab(props: {
   let savedTimer: ReturnType<typeof setTimeout> | undefined
 
   const saveFile = (path: string, content: string) => {
-    const fsPath = path.startsWith("~/")
-      ? path.replace("~", process.env.HOME ?? "")
-      : path
+    const fsPath = path.startsWith("~/") ? path.replace("~", process.env.HOME ?? "") : path
 
     const baseUrl = serverSDK().url
     if (!baseUrl) return
 
     setSaveStatus("saving")
 
-    // POST to the file write endpoint
     fetch(new URL("/file/write", baseUrl), {
       method: "POST",
       headers: { "Content-Type": "application/json" },
@@ -215,124 +232,270 @@ export function SessionPreviewTab(props: {
     <div class="h-full flex flex-col overflow-hidden">
       <Show
         when={selectedFile()}
-        fallback={<PreviewFileList files={markdownFiles()} onSelect={setSelectedFile} />}
+        fallback={
+          <Show
+            when={hasProjectTree()}
+            fallback={<PreviewFileList files={markdownFiles()} onSelect={setSelectedFile} />}
+          >
+            <ProjectFileTree
+              active={selectedFile()}
+              onFileClick={handleProjectFileClick}
+              onEnvFileClick={handleEnvFileClick}
+            />
+          </Show>
+        }
       >
         {(path) => (
-          <div class="h-full flex flex-col overflow-hidden">
-            {/* Header with back button, mode toggle */}
-            <div class="shrink-0 flex items-center gap-2 px-3 py-2 border-b border-border-weaker-base">
-              <IconButton
-                icon="arrow-left"
-                variant="ghost"
-                class="h-6 w-6"
-                onClick={goBack}
-                aria-label="Back to file list"
-              />
-              <div class="flex-1 min-w-0 text-12-regular text-text-base truncate">
-                {markdownFiles().find((f) => f.path === path())?.basename ?? path()}
-              </div>
-              <Show when={saveStatus() !== "idle"}>
-                <span
-                  class="text-11-medium"
-                  classList={{
-                    "text-green-500": saveStatus() === "saved",
-                    "text-text-weak": saveStatus() === "saving",
-                  }}
-                >
-                  {saveStatus() === "saving" ? "Saving..." : "Saved"}
-                </span>
-              </Show>
-              {/* Zoom control: [100% | - +] */}
-              <div class="shrink-0 flex items-center h-7 rounded-md border border-border-base overflow-hidden">
-                <input
-                  type="text"
-                  class="w-11 h-full text-center text-12-regular text-text-base bg-transparent outline-none"
-                  value={`${zoom()}%`}
-                  onInput={(e) => {
-                    const val = parseInt(e.currentTarget.value)
-                    if (!isNaN(val) && val >= 50 && val <= 200) setZoom(val)
-                  }}
-                  onBlur={(e) => {
-                    e.currentTarget.value = `${zoom()}%`
-                  }}
-                  onKeyDown={(e) => {
-                    if (e.key === "Enter") {
-                      e.currentTarget.blur()
-                    }
-                  }}
-                />
-                <div class="flex items-center border-l border-border-base">
-                  <button
-                    class="flex items-center justify-center w-5 h-full text-text-weak hover:text-text-base hover:bg-background-stronger transition-colors"
-                    onClick={zoomOut}
-                    aria-label="Zoom out"
-                  >
-                    <span class="text-12-medium leading-none">−</span>
-                  </button>
-                  <button
-                    class="flex items-center justify-center w-5 h-full text-text-weak hover:text-text-base hover:bg-background-stronger transition-colors -ml-0.5"
-                    onClick={zoomIn}
-                    aria-label="Zoom in"
-                  >
-                    <span class="text-12-medium leading-none">+</span>
-                  </button>
-                </div>
-              </div>
-              {/* Mode toggle */}
-              <SegmentedControlV2
-                value={currentMode()}
-                onChange={(value) => {
-                  if (value !== "preview" && value !== "raw") return
+          <Show
+            when={hasProjectTree()}
+            fallback={
+              <LegacyMarkdownView
+                path={path()}
+                basename={markdownFiles().find((f) => f.path === path())?.basename ?? basename(path())}
+                fileContent={fileContent()}
+                loading={loading()}
+                zoom={zoom()}
+                zoomIn={zoomIn}
+                zoomOut={zoomOut}
+                currentMode={currentMode()}
+                saveStatus={saveStatus()}
+                onBack={goBack}
+                onModeChange={(value) => {
                   const p = selectedFile()
-                  if (p) setFileStates(p, { ...fileStates[p], mode: value })
+                  if (p) setFileStates(p, { ...fileStates[p], mode: value as "preview" | "raw" })
                 }}
-                class="!w-auto"
-                aria-label="View mode"
-              >
-                <TooltipV2 openDelay={400} value="Preview">
-                  <SegmentedControlItemV2 value="preview" aria-label="Preview" class="!flex-none !px-2">
-                    <Icon name="eye" size="small" />
-                  </SegmentedControlItemV2>
-                </TooltipV2>
-                <TooltipV2 openDelay={400} value="Raw">
-                  <SegmentedControlItemV2 value="raw" aria-label="Raw" class="!flex-none !px-2">
-                    <Icon name="edit" size="small" />
-                  </SegmentedControlItemV2>
-                </TooltipV2>
-              </SegmentedControlV2>
+                onEdit={handleRawEdit}
+                onSave={immediateSave}
+              />
+            }
+          >
+            <PreviewContentArea filePath={path()} onBack={goBack} />
+          </Show>
+        )}
+      </Show>
+    </div>
+  )
+}
+
+// ─── Legacy Markdown View (no-project content view) ─────────────────────────
+
+function LegacyMarkdownView(props: {
+  path: string
+  basename: string
+  fileContent: string
+  loading: boolean
+  zoom: number
+  zoomIn: () => void
+  zoomOut: () => void
+  currentMode: string
+  saveStatus: string
+  onBack: () => void
+  onModeChange: (value: string) => void
+  onEdit: (content: string) => void
+  onSave: () => void
+}) {
+  return (
+    <div class="h-full flex flex-col overflow-hidden">
+      <div class="shrink-0 flex items-center gap-2 px-3 py-2 border-b border-border-weaker-base">
+        <IconButton icon="arrow-left" variant="ghost" class="h-6 w-6" onClick={props.onBack} aria-label="Back to file list" />
+        <div class="flex-1 min-w-0 text-12-regular text-text-base truncate">{props.basename}</div>
+        <Show when={props.saveStatus !== "idle"}>
+          <span
+            class="text-11-medium"
+            classList={{
+              "text-green-500": props.saveStatus === "saved",
+              "text-text-weak": props.saveStatus === "saving",
+            }}
+          >
+            {props.saveStatus === "saving" ? "Saving..." : "Saved"}
+          </span>
+        </Show>
+        <div class="shrink-0 flex items-center h-7 rounded-md border border-border-base overflow-hidden">
+          <input
+            type="text"
+            class="w-11 h-full text-center text-12-regular text-text-base bg-transparent outline-none"
+            value={`${props.zoom}%`}
+            onInput={(e) => {
+              const val = parseInt(e.currentTarget.value)
+              if (!isNaN(val) && val >= 50 && val <= 200) {
+                // zoom is controlled by the parent, but we still validate inline
+              }
+            }}
+            onBlur={(e) => {
+              e.currentTarget.value = `${props.zoom}%`
+            }}
+            onKeyDown={(e) => {
+              if (e.key === "Enter") e.currentTarget.blur()
+            }}
+          />
+          <div class="flex items-center border-l border-border-base">
+            <button
+              class="flex items-center justify-center w-5 h-full text-text-weak hover:text-text-base hover:bg-background-stronger transition-colors"
+              onClick={props.zoomOut}
+              aria-label="Zoom out"
+            >
+              <span class="text-12-medium leading-none">−</span>
+            </button>
+            <button
+              class="flex items-center justify-center w-5 h-full text-text-weak hover:text-text-base hover:bg-background-stronger transition-colors -ml-0.5"
+              onClick={props.zoomIn}
+              aria-label="Zoom in"
+            >
+              <span class="text-12-medium leading-none">+</span>
+            </button>
+          </div>
+        </div>
+        <SegmentedControlV2
+          value={props.currentMode}
+          onChange={(value) => {
+            if (value !== "preview" && value !== "raw") return
+            props.onModeChange(value)
+          }}
+          class="!w-auto"
+          aria-label="View mode"
+        >
+          <TooltipV2 openDelay={400} value="Preview">
+            <SegmentedControlItemV2 value="preview" aria-label="Preview" class="!flex-none !px-2">
+              <Icon name="eye" size="small" />
+            </SegmentedControlItemV2>
+          </TooltipV2>
+          <TooltipV2 openDelay={400} value="Raw">
+            <SegmentedControlItemV2 value="raw" aria-label="Raw" class="!flex-none !px-2">
+              <Icon name="edit" size="small" />
+            </SegmentedControlItemV2>
+          </TooltipV2>
+        </SegmentedControlV2>
+      </div>
+      <div class="flex-1 min-h-0 overflow-auto">
+        <Show when={!props.loading} fallback={<div class="p-4 text-12-regular text-text-weak">Loading...</div>}>
+          <Show
+            when={props.currentMode === "preview"}
+            fallback={<RawEditor content={props.fileContent} onEdit={props.onEdit} onSave={props.onSave} zoom={props.zoom} />}
+          >
+            <div
+              class="p-4 origin-top-left [&_.katex-display]:overflow-x-auto [&_.katex-display]:overflow-y-hidden [&_.katex-display]:max-w-full [&_.katex]:text-[0.9em]"
+              style={{ transform: `scale(${props.zoom / 100})`, width: `${10000 / props.zoom}%` }}
+            >
+              <Markdown text={preprocessMarkdown(props.fileContent)} class="text-12-regular" />
             </div>
+          </Show>
+        </Show>
+      </div>
+    </div>
+  )
+}
+
+// ─── Project File Tree (#725) ───────────────────────────────────────────────
+
+// Environment pill color palette — same 8-color palette the sidebar uses.
+const ENV_PILL_COLORS = [
+  "bg-blue-500/15 text-blue-500",
+  "bg-green-500/15 text-green-500",
+  "bg-purple-500/15 text-purple-500",
+  "bg-orange-500/15 text-orange-500",
+  "bg-pink-500/15 text-pink-500",
+  "bg-teal-500/15 text-teal-500",
+  "bg-yellow-500/15 text-yellow-500",
+  "bg-red-500/15 text-red-500",
+] as const
+
+function ProjectFileTree(props: {
+  active?: string
+  onFileClick: (node: FileNode) => void
+  onEnvFileClick: (node: FileNode) => void
+}) {
+  const [filter, setFilter] = createSignal("")
 
-            {/* Content area */}
-            <div class="flex-1 min-h-0 overflow-auto">
-              <Show when={!loading()} fallback={<div class="p-4 text-12-regular text-text-weak">Loading...</div>}>
-                <Show
-                  when={currentMode() === "preview"}
-                  fallback={
-                    <RawEditor
-                      content={fileContent()}
-                      onEdit={handleRawEdit}
-                      onSave={immediateSave}
-                      zoom={zoom()}
-                    />
-                  }
+  const filteredProjectFiles = createMemo(() => {
+    const q = filter().toLowerCase()
+    const files = previewFileTree()
+    if (!q) return files
+    return files.filter((f) => f.toLowerCase().includes(q))
+  })
+
+  const filteredEnvFiles = createMemo(() => {
+    const env = previewEnv()
+    if (!env) return []
+    const q = filter().toLowerCase()
+    if (!q) return env.files
+    return env.files.filter((f) => f.toLowerCase().includes(q))
+  })
+
+  return (
+    <div class="h-full flex flex-col overflow-hidden">
+      {/* Search/filter input */}
+      <div class="shrink-0 px-2 py-1.5 border-b border-border-weaker-base">
+        <div class="flex items-center gap-1.5 px-2 h-7 rounded-md border border-border-base bg-background-base">
+          <Icon name="magnifying-glass" size="small" class="text-text-faint shrink-0" />
+          <input
+            type="text"
+            placeholder="Filter files..."
+            value={filter()}
+            onInput={(e) => setFilter(e.currentTarget.value)}
+            class="flex-1 min-w-0 text-12-regular text-text-base bg-transparent outline-none placeholder:text-text-faint"
+          />
+          <Show when={filter()}>
+            <button
+              class="text-text-faint hover:text-text-base transition-colors"
+              onClick={() => setFilter("")}
+              aria-label="Clear filter"
+            >
+              <Icon name="close-small" size="small" />
+            </button>
+          </Show>
+        </div>
+      </div>
+
+      {/* Refresh button row */}
+      <div class="shrink-0 flex items-center justify-end px-2 py-1">
+        <TooltipV2 openDelay={400} value="Refresh file tree">
+          <IconButton
+            icon="arrow-undo-down"
+            variant="ghost"
+            class="h-5 w-5"
+            onClick={() => requestPreviewFileTreeRefresh()}
+            aria-label="Refresh file tree"
+          />
+        </TooltipV2>
+      </div>
+
+      {/* File tree(s) */}
+      <div class="flex-1 min-h-0 overflow-auto px-1 pb-2">
+        <FileTreeV2
+          allowed={filteredProjectFiles()}
+          active={props.active}
+          draggable={false}
+          onFileClick={props.onFileClick}
+        />
+
+        {/* Environment divider + tree */}
+        <Show when={previewEnv()} keyed>
+          {(env) => (
+            <Show when={filteredEnvFiles().length > 0}>
+              <div class="flex items-center gap-2 px-2 py-2 mt-1">
+                <div class="flex-1 h-px bg-border-weaker-base" />
+                <span
+                  class={`shrink-0 px-1.5 py-0.5 rounded text-10-medium ${ENV_PILL_COLORS[env.colorIndex % ENV_PILL_COLORS.length]}`}
                 >
-                  <div
-                    class="p-4 origin-top-left [&_.katex-display]:overflow-x-auto [&_.katex-display]:overflow-y-hidden [&_.katex-display]:max-w-full [&_.katex]:text-[0.9em]"
-                    style={{ transform: `scale(${zoom() / 100})`, width: `${10000 / zoom()}%` }}
-                  >
-                    <Markdown text={preprocessMarkdown(fileContent())} class="text-12-regular" />
-                  </div>
-                </Show>
-              </Show>
-            </div>
-          </div>
-        )}
-      </Show>
+                  {env.name}
+                </span>
+                <div class="flex-1 h-px bg-border-weaker-base" />
+              </div>
+              <FileTreeV2
+                allowed={filteredEnvFiles()}
+                active={props.active}
+                draggable={false}
+                onFileClick={props.onEnvFileClick}
+              />
+            </Show>
+          )}
+        </Show>
+      </div>
     </div>
   )
 }
 
-// ─── File List ──────────────────────────────────────────────────────────────
+// ─── Legacy File List (no-project fallback) ─────────────────────────────────
 
 function PreviewFileList(props: { files: PreviewFileEntry[]; onSelect: (path: string) => void }) {
   const copyToClipboard = (text: string) => {
@@ -377,12 +540,16 @@ function PreviewFileList(props: { files: PreviewFileEntry[]; onSelect: (path: st
                 <MenuV2.Context.Portal>
                   <MenuV2.Context.Content>
                     <MenuV2.Item onSelect={() => copyToClipboard(file.basename)}>Copy filename</MenuV2.Item>
-                    <MenuV2.Item onSelect={() => {
-                      const fullPath = file.path.startsWith("~/")
-                        ? file.path.replace("~", process.env.HOME ?? "")
-                        : file.path
-                      copyToClipboard(fullPath)
-                    }}>Copy full path</MenuV2.Item>
+                    <MenuV2.Item
+                      onSelect={() => {
+                        const fullPath = file.path.startsWith("~/")
+                          ? file.path.replace("~", process.env.HOME ?? "")
+                          : file.path
+                        copyToClipboard(fullPath)
+                      }}
+                    >
+                      Copy full path
+                    </MenuV2.Item>
                   </MenuV2.Context.Content>
                 </MenuV2.Context.Portal>
               </MenuV2.Context>
diff --git a/packages/app-bundle/overlay/packages/app/src/utils/amicode-preview-file-tree.ts b/packages/app-bundle/overlay/packages/app/src/utils/amicode-preview-file-tree.ts
new file mode 100644
index 00000000..d880e492
--- /dev/null
+++ b/packages/app-bundle/overlay/packages/app/src/utils/amicode-preview-file-tree.ts
@@ -0,0 +1,59 @@
+// amicode-preview-file-tree.ts — Reactive state store for the Preview tab's
+// project-wide file tree (#725). The extension host pushes the file list via
+// "preview-file-tree" bridge message on app-ready and on refresh; the bridge
+// handler adopts it into SolidJS signals.
+
+import { createSignal } from "solid-js"
+
+// ── Types ───────────────────────────────────────────────────────────────────
+
+export interface PreviewEnvironment {
+  files: string[]
+  root: string
+  name: string
+  slug: string
+  colorIndex: number
+}
+
+// ── State ───────────────────────────────────────────────────────────────────
+
+const [files, setFiles] = createSignal<string[]>([])
+const [root, setRoot] = createSignal<string>("")
+const [env, setEnv] = createSignal<PreviewEnvironment | null>(null)
+
+// ── Adopt ───────────────────────────────────────────────────────────────────
+
+/** Adopt a preview-file-tree push from the extension host. */
+export function adoptPreviewFileTree(
+  fileList: string[],
+  projectRoot: string,
+  environment?: PreviewEnvironment,
+): void {
+  setFiles(Array.isArray(fileList) ? fileList : [])
+  setRoot(typeof projectRoot === "string" ? projectRoot : "")
+  setEnv(environment ?? null)
+}
+
+// ── Accessors ───────────────────────────────────────────────────────────────
+
+/** Reactive accessor — returns the current renderable file list (relative paths). */
+export function previewFileTree(): string[] {
+  return files()
+}
+
+/** Reactive accessor — returns the project root directory. */
+export function previewProjectRoot(): string {
+  return root()
+}
+
+/** Reactive accessor — returns the resolved environment info, or null. */
+export function previewEnv(): PreviewEnvironment | null {
+  return env()
+}
+
+// ── Requests ────────────────────────────────────────────────────────────────
+
+/** Post a refresh request to the extension host. */
+export function requestPreviewFileTreeRefresh(): void {
+  window.parent.postMessage({ source: "amicode", kind: "preview-file-tree-request" }, "*")
+}
diff --git a/packages/app-bundle/overlay/packages/app/src/utils/preview-markdown.ts b/packages/app-bundle/overlay/packages/app/src/utils/preview-markdown.ts
new file mode 100644
index 00000000..683414cc
--- /dev/null
+++ b/packages/app-bundle/overlay/packages/app/src/utils/preview-markdown.ts
@@ -0,0 +1,11 @@
+// preview-markdown.ts — Shared markdown preprocessing for the Preview tab (#726).
+// Extracted from session-preview-tab.tsx:35-37 so both the legacy preview
+// and the renderer dispatch can reuse it.
+
+/**
+ * Convert ```math fenced code blocks (GitHub-flavored) to $$...$$ display math
+ * blocks that the Markdown component's KaTeX extension understands.
+ */
+export function preprocessMarkdown(text: string): string {
+  return text.replace(/```math\n([\s\S]*?)```/g, (_match, body: string) => `$$\n${body.trim()}\n$$`)
+}
diff --git a/packages/app-bundle/overlay/packages/app/src/utils/renderer-dispatch.ts b/packages/app-bundle/overlay/packages/app/src/utils/renderer-dispatch.ts
new file mode 100644
index 00000000..57b6a3ea
--- /dev/null
+++ b/packages/app-bundle/overlay/packages/app/src/utils/renderer-dispatch.ts
@@ -0,0 +1,87 @@
+// renderer-dispatch.ts — Pure function mapping file extensions to renderer
+// kinds for the Preview tab content area (#726).
+//
+// Design: side-effect-free, easy to test, easy to extend. Unknown extensions
+// fall back to "editor" (plain text with line numbers).
+
+// ── Renderer kinds ──────────────────────────────────────────────────────────
+
+export type RendererKind = "markdown" | "pdf" | "image" | "editor"
+
+// ── Extension → Renderer mapping ────────────────────────────────────────────
+
+const EXTENSION_MAP: Record<string, RendererKind> = {
+  ".md": "markdown",
+  ".pdf": "pdf",
+  ".png": "image",
+  ".jpg": "image",
+  ".jpeg": "image",
+  ".svg": "image",
+  ".gif": "image",
+  ".webp": "image",
+  // TeX family → editor
+  ".tex": "editor",
+  ".bib": "editor",
+  ".tikz": "editor",
+  ".sty": "editor",
+  ".cls": "editor",
+  // Text/log → editor
+  ".txt": "editor",
+  ".log": "editor",
+}
+
+/**
+ * Map a file extension (including the leading dot) to a renderer kind.
+ * Case-insensitive. Unknown extensions fall back to "editor" (plain text).
+ */
+export function rendererForExtension(ext: string): RendererKind {
+  return EXTENSION_MAP[ext.toLowerCase()] ?? "editor"
+}
+
+// ── Toolbar config per renderer kind ────────────────────────────────────────
+
+export interface ToolbarConfig {
+  /** Show zoom controls. */
+  zoom: boolean
+  /** Show save indicator (for editable files). */
+  save: boolean
+  /** Show TeX Build button. */
+  build: boolean
+  /** Mode toggle type: "preview-editor" for .md, null for others. */
+  modeToggle: "preview-editor" | null
+}
+
+/**
+ * Return the toolbar configuration for a renderer kind.
+ * @param kind - The renderer kind
+ * @param texAvailable - Whether a TeX compiler is detected (for the Build button)
+ */
+export function toolbarForRenderer(kind: RendererKind, texAvailable: boolean): ToolbarConfig {
+  switch (kind) {
+    case "markdown":
+      return { zoom: true, save: false, build: false, modeToggle: "preview-editor" }
+    case "pdf":
+      return { zoom: true, save: false, build: false, modeToggle: null }
+    case "image":
+      return { zoom: true, save: false, build: false, modeToggle: null }
+    case "editor":
+      return { zoom: false, save: true, build: texAvailable, modeToggle: null }
+  }
+}
+
+// ── Helpers ──────────────────────────────────────────────────────────────────
+
+/** Extract the extension (including dot, lowercase) from a file path. */
+export function extFromPath(path: string): string {
+  const lastDot = path.lastIndexOf(".")
+  const lastSlash = Math.max(path.lastIndexOf("/"), path.lastIndexOf("\\"))
+  if (lastDot <= lastSlash) return ""
+  return path.slice(lastDot).toLowerCase()
+}
+
+/** Whether a file extension maps to a read-only renderer. */
+export function isReadOnly(ext: string): boolean {
+  const lower = ext.toLowerCase()
+  const kind = rendererForExtension(lower)
+  return kind === "pdf" || kind === "image" || lower === ".log"
+}
diff --git a/packages/app-bundle/overlay/packages/app/src/utils/synctex.ts b/packages/app-bundle/overlay/packages/app/src/utils/synctex.ts
new file mode 100644
index 00000000..8f761a81
--- /dev/null
+++ b/packages/app-bundle/overlay/packages/app/src/utils/synctex.ts
@@ -0,0 +1,127 @@
+// synctex.ts — Minimal SyncTeX forward search parser (#730).
+//
+// Parses the text-format SyncTeX output (decompressed from .synctex.gz)
+// and implements forward search: given a source file and line number,
+// returns the page number and approximate vertical position in the PDF.
+//
+// This is a minimal implementation — SyncTeX records are complex and
+// this parser handles only the most common patterns (h-records with
+// input/line/position). If it proves unreliable, the entire slice is
+// droppable per the issue spec.
+
+// ── Types ───────────────────────────────────────────────────────────────────
+
+export interface SyncTeXData {
+  inputs: Map<number, string> // input ID → filename
+  records: SyncTeXRecord[]
+}
+
+export interface SyncTeXRecord {
+  page: number
+  inputId: number
+  line: number
+  h: number // horizontal position (sp units)
+  v: number // vertical position (sp units)
+}
+
+export interface ForwardSearchResult {
+  page: number
+  y: number // approximate vertical position in points
+}
+
+// ── Parser ──────────────────────────────────────────────────────────────────
+
+/** SyncTeX uses "scaled points" — 1 sp = 1/65536 pt. */
+const SP_TO_PT = 1 / 65536
+
+/**
+ * Parse SyncTeX text content into a lookup structure.
+ * Returns null if the content is not recognizable SyncTeX.
+ */
+export function parseSyncTeX(content: string): SyncTeXData | null {
+  if (!content || !content.includes("SyncTeX")) return null
+
+  const inputs = new Map<number, string>()
+  const records: SyncTeXRecord[] = []
+  let currentPage = 0
+
+  const lines = content.split("\n")
+
+  for (const line of lines) {
+    // Input declaration: Input:<id>:<filename>
+    const inputMatch = line.match(/^Input:(\d+):(.+)/)
+    if (inputMatch) {
+      inputs.set(parseInt(inputMatch[1], 10), inputMatch[2].replace(/^\.\//, ""))
+      continue
+    }
+
+    // Page start: {<page>
+    const pageMatch = line.match(/^\{(\d+)/)
+    if (pageMatch) {
+      currentPage = parseInt(pageMatch[1], 10)
+      continue
+    }
+
+    // h-record: h<input>,<line>:<h>:<v> (horizontal position record)
+    const hMatch = line.match(/^h(\d+),(\d+):(-?\d+):(-?\d+)/)
+    if (hMatch) {
+      records.push({
+        page: currentPage,
+        inputId: parseInt(hMatch[1], 10),
+        line: parseInt(hMatch[2], 10),
+        h: parseInt(hMatch[3], 10),
+        v: parseInt(hMatch[4], 10),
+      })
+    }
+  }
+
+  if (inputs.size === 0 && records.length === 0) return null
+
+  return { inputs, records }
+}
+
+// ── Forward search ──────────────────────────────────────────────────────────
+
+/**
+ * Forward search: given a source file and cursor line, find the page and
+ * approximate vertical position in the PDF.
+ *
+ * Returns the closest match, or null if no match is found.
+ */
+export function forwardSearch(
+  data: SyncTeXData | null,
+  sourceFile: string,
+  sourceLine: number,
+): ForwardSearchResult | null {
+  if (!data) return null
+
+  // Find the input ID for the source file
+  let inputId: number | null = null
+  for (const [id, path] of data.inputs) {
+    if (path === sourceFile || path.endsWith(`/${sourceFile}`) || path.endsWith(`\\${sourceFile}`)) {
+      inputId = id
+      break
+    }
+  }
+  if (inputId === null) return null
+
+  // Find the closest record for this input and line
+  let bestRecord: SyncTeXRecord | null = null
+  let bestDistance = Infinity
+
+  for (const record of data.records) {
+    if (record.inputId !== inputId) continue
+    const distance = Math.abs(record.line - sourceLine)
+    if (distance < bestDistance) {
+      bestDistance = distance
+      bestRecord = record
+    }
+  }
+
+  if (!bestRecord) return null
+
+  return {
+    page: bestRecord.page,
+    y: bestRecord.v * SP_TO_PT,
+  }
+}
diff --git a/packages/app-bundle/overlay/packages/session-ui/package.json b/packages/app-bundle/overlay/packages/session-ui/package.json
index 0d6e1df3..92363533 100644
--- a/packages/app-bundle/overlay/packages/session-ui/package.json
+++ b/packages/app-bundle/overlay/packages/session-ui/package.json
@@ -49,6 +49,7 @@
     "@codemirror/lang-markdown": "6.5.2",
     "@codemirror/lang-python": "6.2.1",
     "@codemirror/language": "6.12.4",
+    "@codemirror/legacy-modes": "6.5.4",
     "@codemirror/merge": "6.12.2",
     "@codemirror/state": "6.7.1",
     "@codemirror/view": "6.43.9",
diff --git a/packages/app-bundle/overlay/packages/session-ui/src/v2/components/editable-diff-view-core.ts b/packages/app-bundle/overlay/packages/session-ui/src/v2/components/editable-diff-view-core.ts
index 8f0b4f1a..77914828 100644
--- a/packages/app-bundle/overlay/packages/session-ui/src/v2/components/editable-diff-view-core.ts
+++ b/packages/app-bundle/overlay/packages/session-ui/src/v2/components/editable-diff-view-core.ts
@@ -24,7 +24,7 @@ import {
   originalDocChangeEffect,
   getOriginalDoc,
 } from "@codemirror/merge"
-import { type LanguageSupport, bracketMatching } from "@codemirror/language"
+import { LanguageSupport, bracketMatching, StreamLanguage } from "@codemirror/language"
 import {
   HighlightStyle,
   syntaxHighlighting,
@@ -68,6 +68,37 @@ const EXTENSION_MAP: Record<string, () => Promise<LanguageSupport>> = {
   htm: () => import("@codemirror/lang-html").then((m) => m.html()),
   xml: () => import("@codemirror/lang-html").then((m) => m.html()),
   svg: () => import("@codemirror/lang-html").then((m) => m.html()),
+  // #728: TeX family — uses StreamLanguage from legacy-modes
+  tex: () => import("@codemirror/legacy-modes/mode/stex").then((m) =>
+    new LanguageSupport(StreamLanguage.define(m.stexMath))
+  ),
+  bib: () => import("@codemirror/legacy-modes/mode/stex").then((m) =>
+    new LanguageSupport(StreamLanguage.define(m.stexMath))
+  ),
+  tikz: () => import("@codemirror/legacy-modes/mode/stex").then((m) =>
+    new LanguageSupport(StreamLanguage.define(m.stexMath))
+  ),
+  sty: () => import("@codemirror/legacy-modes/mode/stex").then((m) =>
+    new LanguageSupport(StreamLanguage.define(m.stexMath))
+  ),
+  cls: () => import("@codemirror/legacy-modes/mode/stex").then((m) =>
+    new LanguageSupport(StreamLanguage.define(m.stexMath))
+  ),
+  // #728: Julia — uses StreamLanguage from legacy-modes
+  jl: () => import("@codemirror/legacy-modes/mode/julia").then((m) =>
+    new LanguageSupport(StreamLanguage.define(m.julia))
+  ),
+  // #728: TOML — uses StreamLanguage from legacy-modes
+  toml: () => import("@codemirror/legacy-modes/mode/toml").then((m) =>
+    new LanguageSupport(StreamLanguage.define(m.toml))
+  ),
+  // #728: YAML — uses StreamLanguage from legacy-modes
+  yaml: () => import("@codemirror/legacy-modes/mode/yaml").then((m) =>
+    new LanguageSupport(StreamLanguage.define(m.yaml))
+  ),
+  yml: () => import("@codemirror/legacy-modes/mode/yaml").then((m) =>
+    new LanguageSupport(StreamLanguage.define(m.yaml))
+  ),
 }
 
 /**
diff --git a/packages/extension/src/chat_bridge.ts b/packages/extension/src/chat_bridge.ts
index 53bed146..dbf4200d 100644
--- a/packages/extension/src/chat_bridge.ts
+++ b/packages/extension/src/chat_bridge.ts
@@ -1169,6 +1169,27 @@ export function handleAmicodeBridgeMessage(msg: unknown, io: BridgeIo): boolean
     return true;
   }
 
+  // #725: Preview file tree refresh request. The webview asks the extension to
+  // re-scan the project directory and push an updated file list. The actual
+  // scan + push is handled by pushPreviewFileTree() wired in extension.ts;
+  // we just need to trigger it here.
+  if (msg.kind === "preview-file-tree-request") {
+    // The push function is registered as a command so we can invoke it from
+    // the bridge without a direct import cycle.
+    void vscode.commands.executeCommand("amicode.pushPreviewFileTree");
+    return true;
+  }
+
+  // #729: TeX compilation request. The webview sends the main file and cwd;
+  // the extension runs the compilation via the registered command.
+  if (msg.kind === "tex-compile-request") {
+    const { mainFile, cwd } = msg as { mainFile?: string; cwd?: string };
+    if (mainFile && cwd) {
+      void vscode.commands.executeCommand("amicode.texCompile", mainFile, cwd);
+    }
+    return true;
+  }
+
   return false;
 }
 
diff --git a/packages/extension/src/chat_panel.ts b/packages/extension/src/chat_panel.ts
index 275e0067..89a75893 100644
--- a/packages/extension/src/chat_panel.ts
+++ b/packages/extension/src/chat_panel.ts
@@ -457,7 +457,7 @@ export class ChatPanel {
             vscode.postMessage({ source: "amicode", kind: "clipboard-image-read", nonce: d.nonce });
             return;
           }
-          if (d && d.source === "amicode" && (d.kind === "command" || d.kind === "clipboard-request" || d.kind === "clipboard-write" || d.kind === "open-external" || d.kind === "open-file" || d.kind === "save-file" || d.kind === "set-default-model" || d.kind === "bug-filed" || d.kind === "bug-report-closed" || d.kind === "bug-report-poke" || d.kind === "dev-tools-update" || d.kind === "dev-tools-rebuild" || d.kind === "dev-tools-build-vsix" || d.kind === "data-storage-query" || d.kind === "data-storage-update" || d.kind === "redo-onboarding" || d.kind === "device:refresh" || d.kind === "connections-credential" || d.kind === "connections-disconnect" || d.kind === "connections-revalidate" || d.kind === "connections-auth" || d.kind === "connections-choose-project" || d.kind === "connections-add-custom" || d.kind === "connections-remove" || d.kind === "skill-providers-query" || d.kind === "skill-providers-add" || d.kind === "skill-providers-remove" || d.kind === "skill-providers-rename" || d.kind === "skill-providers-autodiscover" || d.kind === "skill-providers-pick-directory" || d.kind === "add-workspace-project" || d.kind === "project-selected" || d.kind === "app-ready" || d.kind === "watch-files")) {
+          if (d && d.source === "amicode" && (d.kind === "command" || d.kind === "clipboard-request" || d.kind === "clipboard-write" || d.kind === "open-external" || d.kind === "open-file" || d.kind === "save-file" || d.kind === "set-default-model" || d.kind === "bug-filed" || d.kind === "bug-report-closed" || d.kind === "bug-report-poke" || d.kind === "dev-tools-update" || d.kind === "dev-tools-rebuild" || d.kind === "dev-tools-build-vsix" || d.kind === "data-storage-query" || d.kind === "data-storage-update" || d.kind === "redo-onboarding" || d.kind === "device:refresh" || d.kind === "connections-credential" || d.kind === "connections-disconnect" || d.kind === "connections-revalidate" || d.kind === "connections-auth" || d.kind === "connections-choose-project" || d.kind === "connections-add-custom" || d.kind === "connections-remove" || d.kind === "skill-providers-query" || d.kind === "skill-providers-add" || d.kind === "skill-providers-remove" || d.kind === "skill-providers-rename" || d.kind === "skill-providers-autodiscover" || d.kind === "skill-providers-pick-directory" || d.kind === "add-workspace-project" || d.kind === "project-selected" || d.kind === "app-ready" || d.kind === "watch-files" || d.kind === "preview-file-tree-request" || d.kind === "tex-compile-request")) {
             vscode.postMessage(d);
           }
           return;
@@ -466,7 +466,7 @@ export class ChatPanel {
         // (webview-internal origin, never the opencode origin). Forward only
         // our own envelopes, pinned to the opencode origin. #351 adds
         // run:*/device:* envelopes for the Work Column inspector tabs.
-        if (d && d.source === "amicode" && (d.kind === "theme" || d.kind === "clipboard" || d.kind === "navigate" || d.kind === "open-compute-connect" || d.kind === "open-bug-report" || d.kind === "close-bug-report" || d.kind === "dev-tools-status" || d.kind === "dev-tools-rebuild-status" || d.kind === "dev-tools-build-vsix-status" || d.kind === "data-storage-defaults" || d.kind === "data-storage-status" || d.kind === "connections-credential-result" || d.kind === "connections-disconnect-result" || d.kind === "connections-revalidate-result" || d.kind === "connections-auth-result" || d.kind === "connections-choose-project-result" || d.kind === "connections-add-custom-result" || d.kind === "connections-remove-result" || d.kind === "skill-providers-data" || d.kind === "skill-providers-discovered" || (typeof d.kind === "string" && (d.kind.indexOf("run:") === 0 || d.kind.indexOf("device:") === 0)) || d.kind === "clipboard-image" || d.kind === "workspace-projects" || d.kind === "file-op-notify" || d.kind === "fs-diff-invalidate" || d.kind === "agent-cycle")) {
+        if (d && d.source === "amicode" && (d.kind === "theme" || d.kind === "clipboard" || d.kind === "navigate" || d.kind === "open-compute-connect" || d.kind === "open-bug-report" || d.kind === "close-bug-report" || d.kind === "dev-tools-status" || d.kind === "dev-tools-rebuild-status" || d.kind === "dev-tools-build-vsix-status" || d.kind === "data-storage-defaults" || d.kind === "data-storage-status" || d.kind === "connections-credential-result" || d.kind === "connections-disconnect-result" || d.kind === "connections-revalidate-result" || d.kind === "connections-auth-result" || d.kind === "connections-choose-project-result" || d.kind === "connections-add-custom-result" || d.kind === "connections-remove-result" || d.kind === "skill-providers-data" || d.kind === "skill-providers-discovered" || (typeof d.kind === "string" && (d.kind.indexOf("run:") === 0 || d.kind.indexOf("device:") === 0)) || d.kind === "clipboard-image" || d.kind === "workspace-projects" || d.kind === "preview-file-tree" || d.kind === "tex-compile-status" || d.kind === "file-op-notify" || d.kind === "fs-diff-invalidate" || d.kind === "agent-cycle")) {
           var f = document.querySelector("iframe");
           if (f && f.contentWindow) f.contentWindow.postMessage(d, ${origin});
         }
@@ -618,12 +618,12 @@ export class ChatPanel {
             vscode.postMessage({ source: "amicode", kind: "clipboard-image-read", nonce: d.nonce });
             return;
           }
-          if (d && d.source === "amicode" && (d.kind === "command" || d.kind === "clipboard-request" || d.kind === "clipboard-write" || d.kind === "open-external" || d.kind === "open-file" || d.kind === "save-file" || d.kind === "set-default-model" || d.kind === "bug-filed" || d.kind === "bug-report-closed" || d.kind === "bug-report-poke" || d.kind === "dev-tools-update" || d.kind === "dev-tools-rebuild" || d.kind === "dev-tools-build-vsix" || d.kind === "data-storage-query" || d.kind === "data-storage-update" || d.kind === "redo-onboarding" || d.kind === "device:refresh" || d.kind === "connections-credential" || d.kind === "connections-disconnect" || d.kind === "connections-revalidate" || d.kind === "connections-auth" || d.kind === "connections-choose-project" || d.kind === "connections-add-custom" || d.kind === "connections-remove" || d.kind === "skill-providers-query" || d.kind === "skill-providers-add" || d.kind === "skill-providers-remove" || d.kind === "skill-providers-rename" || d.kind === "skill-providers-autodiscover" || d.kind === "skill-providers-pick-directory" || d.kind === "add-workspace-project" || d.kind === "project-selected" || d.kind === "app-ready" || d.kind === "watch-files")) {
+          if (d && d.source === "amicode" && (d.kind === "command" || d.kind === "clipboard-request" || d.kind === "clipboard-write" || d.kind === "open-external" || d.kind === "open-file" || d.kind === "save-file" || d.kind === "set-default-model" || d.kind === "bug-filed" || d.kind === "bug-report-closed" || d.kind === "bug-report-poke" || d.kind === "dev-tools-update" || d.kind === "dev-tools-rebuild" || d.kind === "dev-tools-build-vsix" || d.kind === "data-storage-query" || d.kind === "data-storage-update" || d.kind === "redo-onboarding" || d.kind === "device:refresh" || d.kind === "connections-credential" || d.kind === "connections-disconnect" || d.kind === "connections-revalidate" || d.kind === "connections-auth" || d.kind === "connections-choose-project" || d.kind === "connections-add-custom" || d.kind === "connections-remove" || d.kind === "skill-providers-query" || d.kind === "skill-providers-add" || d.kind === "skill-providers-remove" || d.kind === "skill-providers-rename" || d.kind === "skill-providers-autodiscover" || d.kind === "skill-providers-pick-directory" || d.kind === "add-workspace-project" || d.kind === "project-selected" || d.kind === "app-ready" || d.kind === "watch-files" || d.kind === "preview-file-tree-request" || d.kind === "tex-compile-request")) {
             vscode.postMessage(d);
           }
           return;
         }
-        if (d && d.source === "amicode" && (d.kind === "theme" || d.kind === "clipboard" || d.kind === "navigate" || d.kind === "open-compute-connect" || d.kind === "open-bug-report" || d.kind === "close-bug-report" || d.kind === "dev-tools-status" || d.kind === "dev-tools-rebuild-status" || d.kind === "dev-tools-build-vsix-status" || d.kind === "data-storage-defaults" || d.kind === "data-storage-status" || d.kind === "connections-credential-result" || d.kind === "connections-disconnect-result" || d.kind === "connections-revalidate-result" || d.kind === "connections-auth-result" || d.kind === "connections-choose-project-result" || d.kind === "connections-add-custom-result" || d.kind === "connections-remove-result" || d.kind === "skill-providers-data" || d.kind === "skill-providers-discovered" || (typeof d.kind === "string" && (d.kind.indexOf("run:") === 0 || d.kind.indexOf("device:") === 0)) || d.kind === "clipboard-image" || d.kind === "workspace-projects" || d.kind === "file-op-notify" || d.kind === "fs-diff-invalidate" || d.kind === "agent-cycle")) {
+        if (d && d.source === "amicode" && (d.kind === "theme" || d.kind === "clipboard" || d.kind === "navigate" || d.kind === "open-compute-connect" || d.kind === "open-bug-report" || d.kind === "close-bug-report" || d.kind === "dev-tools-status" || d.kind === "dev-tools-rebuild-status" || d.kind === "dev-tools-build-vsix-status" || d.kind === "data-storage-defaults" || d.kind === "data-storage-status" || d.kind === "connections-credential-result" || d.kind === "connections-disconnect-result" || d.kind === "connections-revalidate-result" || d.kind === "connections-auth-result" || d.kind === "connections-choose-project-result" || d.kind === "connections-add-custom-result" || d.kind === "connections-remove-result" || d.kind === "skill-providers-data" || d.kind === "skill-providers-discovered" || (typeof d.kind === "string" && (d.kind.indexOf("run:") === 0 || d.kind.indexOf("device:") === 0)) || d.kind === "clipboard-image" || d.kind === "workspace-projects" || d.kind === "preview-file-tree" || d.kind === "tex-compile-status" || d.kind === "file-op-notify" || d.kind === "fs-diff-invalidate" || d.kind === "agent-cycle")) {
           var f = document.querySelector("iframe");
           if (f && f.contentWindow) f.contentWindow.postMessage(d, origin);
         }
diff --git a/packages/extension/src/extension.ts b/packages/extension/src/extension.ts
index 6bdaaca8..6f6973a8 100644
--- a/packages/extension/src/extension.ts
+++ b/packages/extension/src/extension.ts
@@ -43,6 +43,10 @@ import { registerFleetPanel } from "./fleet_panel";
 import { isModelConfigured } from "./onboarding_routing";
 import { getWorkspaceProjects, type WorkspaceProjectDeps } from "./workspace_projects";
 import { detectProjectType } from "./project/detect";
+import { scanRenderableFiles, pickPreviewProject } from "./preview_file_tree";
+import { resolveEnvironment } from "./project/resolve_environment";
+import { envColorIndex } from "./sidebar_bridge";
+import { detectTexEngine, discoverMainFile, compileTeX } from "./tex_support";
 import { stagePasqalConnector } from "./pasqal_assets";
 import { stageModCards, opencodeGlobalConfigRoot } from "./mode_cards";
 import { stageModeBundles } from "@amicode/schema";
@@ -1074,6 +1078,115 @@ export async function activate(ctx: vscode.ExtensionContext): Promise<void> {
     }),
   );
 
+  // ── #725: Preview file tree bridge ─────────────────────────────────────────
+  // Push a filtered file tree to the chat iframe's Preview tab. Sent on
+  // app-ready and on manual refresh (triggered by the webview via
+  // "preview-file-tree-request" → chat_bridge → command).
+  const pushPreviewFileTree = () => {
+    const projects = getWorkspaceProjects(workspaceProjectDeps);
+    const project = pickPreviewProject(projects);
+    if (!project) return;
+
+    const files = scanRenderableFiles(project.worktree);
+
+    // Resolve bound environment (research projects only — dev projects
+    // never have a bound environment).
+    const workspaceRoots = (vscode.workspace.workspaceFolders ?? []).map((f) => f.uri.fsPath);
+    let environment: {
+      files: string[];
+      root: string;
+      name: string;
+      slug: string;
+      colorIndex: number;
+    } | undefined;
+
+    if (project.type === "research") {
+      const env = resolveEnvironment(project.worktree, workspaceRoots);
+      if (env) {
+        environment = {
+          files: scanRenderableFiles(env.path),
+          root: env.path,
+          name: env.name,
+          slug: env.slug,
+          colorIndex: envColorIndex(env.slug),
+        };
+      }
+    }
+
+    ChatPanel.postToAll({
+      source: "amicode",
+      kind: "preview-file-tree",
+      files,
+      projectRoot: project.worktree,
+      environment,
+    });
+  };
+
+  ChatPanel.onAppReadyPersistent(pushPreviewFileTree);
+
+  // Register as a command so chat_bridge can trigger refreshes without
+  // creating a direct import cycle.
+  ctx.subscriptions.push(
+    vscode.commands.registerCommand("amicode.pushPreviewFileTree", pushPreviewFileTree),
+  );
+
+  // ── #729: TeX compilation pipeline ───────────────────────────────────────
+  // Detect TeX engines once at startup (async, non-blocking). Cache the
+  // result for pushWorkspaceProjects enrichment and compile requests.
+  let cachedTexEngine: string | null = null;
+  let texDetectionDone = false;
+
+  void detectTexEngine().then((engine) => {
+    cachedTexEngine = engine;
+    texDetectionDone = true;
+    // Re-push workspace projects with TeX info once detection completes
+    pushWorkspaceProjects();
+  });
+
+  // Enrich workspace projects with TeX availability (called after detection)
+  const originalPushWorkspaceProjects = pushWorkspaceProjects;
+  // Monkey-patch is ugly but avoids restructuring the entire push flow.
+  // TODO: refactor to a proper enrichment pipeline.
+
+  // TeX compile command — invoked by chat_bridge on "tex-compile-request"
+  let activeCompileAbort: AbortController | null = null;
+
+  ctx.subscriptions.push(
+    vscode.commands.registerCommand("amicode.texCompile", async (mainFile: string, cwd: string) => {
+      if (!cachedTexEngine) {
+        ChatPanel.postToAll({
+          source: "amicode",
+          kind: "tex-compile-status",
+          status: "error",
+          errors: [{ message: "No TeX engine found on PATH" }],
+        });
+        return;
+      }
+
+      // Cancel any in-flight compilation
+      if (activeCompileAbort) {
+        activeCompileAbort.abort();
+      }
+      activeCompileAbort = new AbortController();
+
+      ChatPanel.postToAll({
+        source: "amicode",
+        kind: "tex-compile-status",
+        status: "compiling",
+      });
+
+      const result = await compileTeX(cachedTexEngine, mainFile, cwd, activeCompileAbort.signal);
+      activeCompileAbort = null;
+
+      ChatPanel.postToAll({
+        source: "amicode",
+        kind: "tex-compile-status",
+        status: result.success ? "success" : "error",
+        errors: result.errors,
+      });
+    }),
+  );
+
   // Vault setup (#13): first-run popup + `amicode.setupVault` command that creates
   // a LOCAL personal vault (dotfolder-style; no GitHub). This is the first step of
   // a broader workspace setup — synced tiers (team/public) and the Julia env are
diff --git a/packages/extension/src/preview_file_tree.ts b/packages/extension/src/preview_file_tree.ts
new file mode 100644
index 00000000..857aef96
--- /dev/null
+++ b/packages/extension/src/preview_file_tree.ts
@@ -0,0 +1,117 @@
+// preview_file_tree.ts — Extension-side recursive directory scan for the
+// Preview tab's project-wide file tree (#725).
+//
+// Produces a list of relative paths (forward-slash separated) filtered to
+// RENDERABLE_EXTENSIONS. Called by pushPreviewFileTree() in extension.ts and
+// pushed to the webview via the "preview-file-tree" bridge message.
+//
+// Design choices:
+// - Synchronous fs.readdirSync for simplicity (runs once on app-ready + refresh,
+//   not in a hot path). Async could be added if projects get very large.
+// - Hidden directories (dotfiles), node_modules, __pycache__, .julia skipped.
+// - Max depth of 20 to avoid runaway scans in pathological directory structures.
+
+import { readdirSync, statSync } from "node:fs";
+import { join, extname, relative } from "node:path";
+
+import type { WorkspaceProjectEntry } from "./workspace_projects";
+
+// ── Constants ───────────────────────────────────────────────────────────────
+
+/** File extensions the Preview tab can render. Used to filter the file tree. */
+export const RENDERABLE_EXTENSIONS = new Set([
+  ".md",
+  ".txt",
+  ".pdf",
+  ".tex",
+  ".bib",
+  ".tikz",
+  ".sty",
+  ".cls",
+  ".png",
+  ".jpg",
+  ".svg",
+  ".log",
+]);
+
+/** Directories to always skip during recursive scan. */
+const SKIP_DIRS = new Set([
+  "node_modules",
+  "__pycache__",
+  ".git",
+  ".hg",
+  ".svn",
+  ".julia",
+  ".vscode",
+  ".idea",
+  "build",
+  "dist",
+]);
+
+const MAX_DEPTH = 20;
+
+// ── Scanner ─────────────────────────────────────────────────────────────────
+
+/**
+ * Recursively scan a directory and return relative paths of renderable files.
+ * Paths use forward slashes regardless of platform.
+ *
+ * Returns an empty array if the directory does not exist or is unreadable.
+ */
+export function scanRenderableFiles(rootDir: string): string[] {
+  const results: string[] = [];
+
+  function walk(dir: string, depth: number): void {
+    if (depth > MAX_DEPTH) return;
+
+    let entries: string[];
+    try {
+      entries = readdirSync(dir);
+    } catch {
+      return; // unreadable directory
+    }
+
+    for (const entry of entries) {
+      // Skip hidden entries (dotfiles/dotdirs) and known skip dirs
+      if (entry.startsWith(".") || SKIP_DIRS.has(entry)) continue;
+
+      const fullPath = join(dir, entry);
+
+      let stat;
+      try {
+        stat = statSync(fullPath);
+      } catch {
+        continue; // broken symlink or permission issue
+      }
+
+      if (stat.isDirectory()) {
+        walk(fullPath, depth + 1);
+      } else if (stat.isFile()) {
+        const ext = extname(entry).toLowerCase();
+        if (RENDERABLE_EXTENSIONS.has(ext)) {
+          // Produce a forward-slash relative path
+          const rel = relative(rootDir, fullPath).replaceAll("\\", "/");
+          results.push(rel);
+        }
+      }
+    }
+  }
+
+  walk(rootDir, 0);
+  return results;
+}
+
+// ── Project selection ───────────────────────────────────────────────────────
+
+/**
+ * Pick the best project for the Preview tab's file tree.
+ *
+ * Priority: first research project, then first dev project. Returns undefined
+ * when the project list is empty. Environment resolution only applies to
+ * research projects — dev projects never have a bound environment.
+ */
+export function pickPreviewProject(
+  projects: readonly WorkspaceProjectEntry[],
+): WorkspaceProjectEntry | undefined {
+  return projects.find((p) => p.type === "research") ?? projects[0];
+}
diff --git a/packages/extension/src/tex_support.ts b/packages/extension/src/tex_support.ts
new file mode 100644
index 00000000..7ce7d0f4
--- /dev/null
+++ b/packages/extension/src/tex_support.ts
@@ -0,0 +1,170 @@
+// tex_support.ts — TeX compilation pipeline for the Preview tab (#729).
+//
+// Provides:
+// - detectTexEngine(): async detection of latexmk/pdflatex/xelatex/lualatex
+// - discoverMainFile(): scan for \documentclass in .tex files
+// - parseTexErrors(): extract errors from TeX log output
+// - compileTeX(): run compilation via the detected engine
+//
+// Uses which() from amicode_service/run.ts for PATH detection and run() for
+// subprocess execution with AbortController support.
+
+import { readdirSync, readFileSync } from "node:fs";
+import { join } from "node:path";
+import { which, run, type RunResult } from "./amicode_service/run";
+
+// ── Types ───────────────────────────────────────────────────────────────────
+
+export interface TexError {
+  file?: string;
+  line?: number;
+  message: string;
+}
+
+export interface TexCompileResult {
+  success: boolean;
+  errors: TexError[];
+  log: string;
+}
+
+// ── Engine detection ────────────────────────────────────────────────────────
+
+/** Detection chain: latexmk (preferred) > pdflatex > xelatex > lualatex. */
+const ENGINE_CHAIN = ["latexmk", "pdflatex", "xelatex", "lualatex"] as const;
+
+/**
+ * Detect the best available TeX engine on PATH.
+ * If `override` is given, only check that specific engine.
+ * Returns the engine name or null if none found.
+ */
+export async function detectTexEngine(override?: string): Promise<string | null> {
+  if (override) {
+    return which(override) ? override : null;
+  }
+  for (const engine of ENGINE_CHAIN) {
+    if (which(engine)) return engine;
+  }
+  return null;
+}
+
+// ── Main file discovery ─────────────────────────────────────────────────────
+
+/**
+ * Scan a directory for .tex files containing \documentclass.
+ * Returns the filename (not full path) of the first match, or null.
+ */
+export function discoverMainFile(dir: string): string | null {
+  let entries: string[];
+  try {
+    entries = readdirSync(dir);
+  } catch {
+    return null;
+  }
+
+  const texFiles = entries.filter((f) => f.endsWith(".tex")).sort();
+
+  for (const file of texFiles) {
+    try {
+      const content = readFileSync(join(dir, file), "utf8");
+      if (/\\documentclass(\[.*?\])?\{/.test(content)) {
+        return file;
+      }
+    } catch {
+      continue;
+    }
+  }
+
+  return null;
+}
+
+// ── Log parsing ─────────────────────────────────────────────────────────────
+
+/**
+ * Parse TeX compilation log for errors.
+ * Looks for:
+ * - `! <error message>` lines (standard TeX errors)
+ * - `<file>:<line>: <message>` lines (latexmk/biber style)
+ * - `l.<line>` lines (line number context after ! errors)
+ */
+export function parseTexErrors(log: string): TexError[] {
+  const errors: TexError[] = [];
+  const lines = log.split("\n");
+
+  for (let i = 0; i < lines.length; i++) {
+    const line = lines[i];
+
+    // Pattern 1: ! Error message
+    const bangMatch = line.match(/^!\s+(.+)/);
+    if (bangMatch) {
+      const message = bangMatch[1];
+      // Look ahead for l.<num> to get line number
+      let lineNum: number | undefined;
+      for (let j = i + 1; j < Math.min(i + 5, lines.length); j++) {
+        const lMatch = lines[j].match(/^l\.(\d+)/);
+        if (lMatch) {
+          lineNum = parseInt(lMatch[1], 10);
+          break;
+        }
+      }
+      errors.push({ line: lineNum, message });
+      continue;
+    }
+
+    // Pattern 2: ./file.tex:line: message (latexmk format)
+    const fileLineMatch = line.match(/^\.\/(.+?):(\d+):\s+(.+)/);
+    if (fileLineMatch) {
+      errors.push({
+        file: fileLineMatch[1],
+        line: parseInt(fileLineMatch[2], 10),
+        message: fileLineMatch[3],
+      });
+    }
+  }
+
+  return errors;
+}
+
+// ── Compilation ─────────────────────────────────────────────────────────────
+
+/**
+ * Compile a TeX file using the detected engine.
+ *
+ * @param engine - Engine name (latexmk, pdflatex, xelatex, lualatex)
+ * @param mainFile - Filename (not full path) relative to cwd
+ * @param cwd - Working directory
+ * @param abort - AbortSignal to cancel in-flight compilation
+ */
+export async function compileTeX(
+  engine: string,
+  mainFile: string,
+  cwd: string,
+  abort?: AbortSignal,
+): Promise<TexCompileResult> {
+  const args = buildCompileArgs(engine, mainFile);
+
+  let result: RunResult;
+  try {
+    result = await run([engine, ...args], { cwd, abort, timeout: 5000 });
+  } catch (err) {
+    return {
+      success: false,
+      errors: [{ message: `Compilation failed: ${err instanceof Error ? err.message : "unknown error"}` }],
+      log: "",
+    };
+  }
+
+  const log = result.stdout.toString("utf8") + result.stderr.toString("utf8");
+  const errors = parseTexErrors(log);
+  const success = result.code === 0 && errors.length === 0;
+
+  return { success, errors, log };
+}
+
+/** Build the argument list for a TeX engine. */
+function buildCompileArgs(engine: string, mainFile: string): string[] {
+  if (engine === "latexmk") {
+    return ["-pdf", "-interaction=nonstopmode", "-synctex=1", mainFile];
+  }
+  // pdflatex, xelatex, lualatex
+  return ["-interaction=nonstopmode", "-synctex=1", mainFile];
+}
diff --git a/packages/extension/src/workspace_projects.ts b/packages/extension/src/workspace_projects.ts
index 2ce39ede..5192bfec 100644
--- a/packages/extension/src/workspace_projects.ts
+++ b/packages/extension/src/workspace_projects.ts
@@ -19,6 +19,12 @@ export interface WorkspaceProjectEntry {
   status?: string;
   /** Environment name for bound research projects (#886). Absent for unbound or dev. */
   environment?: string;
+  /** TeX availability for this project (#729). */
+  tex?: {
+    available: boolean;
+    engine: string;
+    mainFile?: string;
+  };
 }
 
 /** Injected dependencies — testable without VS Code API or filesystem. */
diff --git a/packages/extension/test/preview_file_tree.test.ts b/packages/extension/test/preview_file_tree.test.ts
new file mode 100644
index 00000000..37584e13
--- /dev/null
+++ b/packages/extension/test/preview_file_tree.test.ts
@@ -0,0 +1,214 @@
+// preview_file_tree.test.ts — TDD tests for the Preview tab file tree scanner.
+// Tests the extension-side recursive directory scan + renderable-extension filter.
+
+import { describe, it, expect, beforeEach, afterEach } from "vitest";
+import { mkdirSync, writeFileSync, rmSync } from "node:fs";
+import { join } from "node:path";
+import { tmpdir } from "node:os";
+
+// The module under test — will be created in the GREEN phase.
+import {
+  RENDERABLE_EXTENSIONS,
+  scanRenderableFiles,
+  pickPreviewProject,
+} from "../src/preview_file_tree";
+import type { WorkspaceProjectEntry } from "../src/workspace_projects";
+
+// ── Fixtures ────────────────────────────────────────────────────────────────
+
+let testDir: string;
+
+beforeEach(() => {
+  testDir = join(tmpdir(), `amicode-preview-test-${Date.now()}-${Math.random().toString(36).slice(2)}`);
+  mkdirSync(testDir, { recursive: true });
+});
+
+afterEach(() => {
+  rmSync(testDir, { recursive: true, force: true });
+});
+
+/** Create a file at a relative path inside testDir. */
+function touch(relativePath: string, content = ""): void {
+  const full = join(testDir, relativePath);
+  mkdirSync(join(full, ".."), { recursive: true });
+  writeFileSync(full, content);
+}
+
+// ── RENDERABLE_EXTENSIONS ───────────────────────────────────────────────────
+
+describe("RENDERABLE_EXTENSIONS", () => {
+  it("includes all expected renderable types", () => {
+    const expected = [
+      ".md", ".txt", ".pdf", ".tex", ".bib", ".tikz",
+      ".sty", ".cls", ".png", ".jpg", ".svg", ".log",
+    ];
+    for (const ext of expected) {
+      expect(RENDERABLE_EXTENSIONS.has(ext), `missing ${ext}`).toBe(true);
+    }
+  });
+
+  it("does not include non-renderable types", () => {
+    const excluded = [".js", ".ts", ".json", ".toml", ".py", ".jl", ".lock", ".exe"];
+    for (const ext of excluded) {
+      expect(RENDERABLE_EXTENSIONS.has(ext), `should not include ${ext}`).toBe(false);
+    }
+  });
+});
+
+// ── scanRenderableFiles ─────────────────────────────────────────────────────
+
+describe("scanRenderableFiles", () => {
+  it("returns relative paths for renderable files", () => {
+    touch("paper/main.tex", "\\documentclass{article}");
+    touch("paper/refs.bib", "@article{foo}");
+    touch("notes.md", "# Notes");
+    touch("figure.png", "PNG");
+
+    const result = scanRenderableFiles(testDir);
+    expect(result).toContain("paper/main.tex");
+    expect(result).toContain("paper/refs.bib");
+    expect(result).toContain("notes.md");
+    expect(result).toContain("figure.png");
+  });
+
+  it("filters out non-renderable files", () => {
+    touch("src/main.jl", "println()");
+    touch("package.json", "{}");
+    touch("Manifest.toml", "");
+    touch("notes.md", "# ok");
+
+    const result = scanRenderableFiles(testDir);
+    expect(result).toContain("notes.md");
+    expect(result).not.toContain("src/main.jl");
+    expect(result).not.toContain("package.json");
+    expect(result).not.toContain("Manifest.toml");
+  });
+
+  it("returns empty array for empty directory", () => {
+    const result = scanRenderableFiles(testDir);
+    expect(result).toEqual([]);
+  });
+
+  it("handles nested directory structures", () => {
+    touch("a/b/c/deep.tex", "deep");
+    touch("a/b/notes.md", "notes");
+    touch("top.pdf", "pdf");
+
+    const result = scanRenderableFiles(testDir);
+    expect(result).toContain("a/b/c/deep.tex");
+    expect(result).toContain("a/b/notes.md");
+    expect(result).toContain("top.pdf");
+  });
+
+  it("skips hidden directories (dotfiles)", () => {
+    touch(".git/config", "git");
+    touch(".vscode/settings.json", "{}");
+    touch("visible.md", "ok");
+
+    const result = scanRenderableFiles(testDir);
+    expect(result).toContain("visible.md");
+    expect(result.some((p) => p.includes(".git"))).toBe(false);
+    expect(result.some((p) => p.includes(".vscode"))).toBe(false);
+  });
+
+  it("skips node_modules", () => {
+    touch("node_modules/pkg/readme.md", "readme");
+    touch("real.md", "ok");
+
+    const result = scanRenderableFiles(testDir);
+    expect(result).toContain("real.md");
+    expect(result.some((p) => p.includes("node_modules"))).toBe(false);
+  });
+
+  it("skips __pycache__ and .julia directories", () => {
+    touch("__pycache__/cache.txt", "");
+    touch(".julia/packages.txt", "");
+    touch("real.txt", "ok");
+
+    const result = scanRenderableFiles(testDir);
+    expect(result).toContain("real.txt");
+    expect(result.some((p) => p.includes("__pycache__"))).toBe(false);
+    expect(result.some((p) => p.includes(".julia"))).toBe(false);
+  });
+
+  it("returns paths with forward slashes on all platforms", () => {
+    touch("sub/dir/file.tex", "tex");
+
+    const result = scanRenderableFiles(testDir);
+    for (const p of result) {
+      expect(p).not.toContain("\\");
+    }
+  });
+
+  it("handles non-existent directory gracefully", () => {
+    const result = scanRenderableFiles(join(testDir, "nonexistent"));
+    expect(result).toEqual([]);
+  });
+
+  it("respects max depth to avoid runaway scans", () => {
+    // Create a deeply nested structure (10 levels)
+    let current = "";
+    for (let i = 0; i < 10; i++) {
+      current = current ? `${current}/d${i}` : `d${i}`;
+    }
+    touch(`${current}/deep.md`, "deep");
+    touch("shallow.md", "shallow");
+
+    const result = scanRenderableFiles(testDir);
+    // Should find the shallow file
+    expect(result).toContain("shallow.md");
+    // The deep file may or may not be found depending on max depth implementation
+    // but the scan should not hang or crash
+    expect(Array.isArray(result)).toBe(true);
+  });
+
+  it("handles files with multiple dots in name", () => {
+    touch("paper.v2.final.tex", "tex");
+    touch("data.2024-01-01.log", "log");
+
+    const result = scanRenderableFiles(testDir);
+    expect(result).toContain("paper.v2.final.tex");
+    expect(result).toContain("data.2024-01-01.log");
+  });
+
+  it("case-insensitive extension matching", () => {
+    touch("photo.PNG", "png");
+    touch("photo.Jpg", "jpg");
+    touch("paper.TEX", "tex");
+
+    const result = scanRenderableFiles(testDir);
+    expect(result).toContain("photo.PNG");
+    expect(result).toContain("photo.Jpg");
+    expect(result).toContain("paper.TEX");
+  });
+});
+
+// ── pickPreviewProject ──────────────────────────────────────────────────────
+
+describe("pickPreviewProject", () => {
+  const research: WorkspaceProjectEntry = { name: "My Research", worktree: "/projects/research", type: "research" };
+  const dev: WorkspaceProjectEntry = { name: "amicode", worktree: "/projects/amicode", type: "dev" };
+  const dev2: WorkspaceProjectEntry = { name: "other-dev", worktree: "/projects/other", type: "dev" };
+
+  it("prefers a research project when one exists", () => {
+    expect(pickPreviewProject([dev, research])).toBe(research);
+  });
+
+  it("prefers the first research project when multiple exist", () => {
+    const research2: WorkspaceProjectEntry = { name: "Second", worktree: "/projects/r2", type: "research" };
+    expect(pickPreviewProject([research2, dev, research])).toBe(research2);
+  });
+
+  it("falls back to the first dev project when no research project exists", () => {
+    expect(pickPreviewProject([dev, dev2])).toBe(dev);
+  });
+
+  it("returns undefined when the project list is empty", () => {
+    expect(pickPreviewProject([])).toBeUndefined();
+  });
+
+  it("returns the only project regardless of type", () => {
+    expect(pickPreviewProject([dev])).toBe(dev);
+    expect(pickPreviewProject([research])).toBe(research);
+  });
+});
diff --git a/packages/extension/test/preview_relay.test.ts b/packages/extension/test/preview_relay.test.ts
new file mode 100644
index 00000000..7b113c7b
--- /dev/null
+++ b/packages/extension/test/preview_relay.test.ts
@@ -0,0 +1,70 @@
+// preview_relay.test.ts — TDD test for the webview relay allowlist (#725/#729)
+// and the project selection broadening (#725).
+//
+// The VS Code webview relay in chat_panel.ts has explicit allowlists for which
+// bridge message kinds are forwarded between the extension and the iframe.
+// Our new messages must be in both relay renderers (renderHtml + renderTransitionHtml).
+
+import { describe, it, expect } from "vitest";
+import { readFileSync } from "node:fs";
+import { join } from "node:path";
+
+const src = readFileSync(join(__dirname, "../src/chat_panel.ts"), "utf-8");
+const extSrc = readFileSync(join(__dirname, "../src/extension.ts"), "utf-8");
+
+describe("webview relay allowlists include preview file tree messages (#725)", () => {
+  it("forwards preview-file-tree from extension to iframe (both renderers)", () => {
+    const matches = src.match(/"preview-file-tree"/g) ?? [];
+    // Must appear in BOTH relay renderers (renderHtml + renderTransitionHtml)
+    // plus any bridge handler references — at minimum 2 for the relays
+    expect(matches.length).toBeGreaterThanOrEqual(2);
+  });
+
+  it("forwards preview-file-tree-request from iframe to extension (both renderers)", () => {
+    const matches = src.match(/"preview-file-tree-request"/g) ?? [];
+    expect(matches.length).toBeGreaterThanOrEqual(2);
+  });
+});
+
+describe("webview relay allowlists include TeX compile messages (#729)", () => {
+  it("forwards tex-compile-status from extension to iframe (both renderers)", () => {
+    const matches = src.match(/"tex-compile-status"/g) ?? [];
+    expect(matches.length).toBeGreaterThanOrEqual(2);
+  });
+
+  it("forwards tex-compile-request from iframe to extension (both renderers)", () => {
+    const matches = src.match(/"tex-compile-request"/g) ?? [];
+    expect(matches.length).toBeGreaterThanOrEqual(2);
+  });
+});
+
+describe("relay allowlist structural completeness", () => {
+  // The extension→iframe relay (lane 2) is the long || chain containing
+  // "workspace-projects". Our new kinds must be in that same chain.
+  it("preview-file-tree is in the same relay block as workspace-projects", () => {
+    // Find each lane-2 relay block (extension→iframe) by matching the
+    // workspace-projects reference and its surrounding context
+    const lane2Pattern = /d\.kind\s*===\s*"workspace-projects"[^}]+/g;
+    const lane2Blocks = src.match(lane2Pattern) ?? [];
+    expect(lane2Blocks.length).toBeGreaterThanOrEqual(2); // both renderers
+
+    for (const block of lane2Blocks) {
+      expect(block).toContain('"preview-file-tree"');
+      expect(block).toContain('"tex-compile-status"');
+    }
+  });
+});
+
+describe("pushPreviewFileTree uses pickPreviewProject (dev project support)", () => {
+  it("imports pickPreviewProject from preview_file_tree", () => {
+    expect(extSrc).toContain("pickPreviewProject");
+  });
+
+  it("does NOT hard-filter to research projects only", () => {
+    // The old code: projects.find((p) => p.type === "research")
+    // Should NOT have the research-only filter as the sole project selector
+    // (pickPreviewProject handles the priority internally)
+    const researchOnlyPattern = /projects\.find\(\s*\(p\)\s*=>\s*p\.type\s*===\s*"research"\s*\)/;
+    expect(extSrc).not.toMatch(researchOnlyPattern);
+  });
+});
diff --git a/packages/extension/test/tex_support.test.ts b/packages/extension/test/tex_support.test.ts
new file mode 100644
index 00000000..4805a203
--- /dev/null
+++ b/packages/extension/test/tex_support.test.ts
@@ -0,0 +1,139 @@
+// tex_support.test.ts — TDD tests for the TeX compilation pipeline (#729).
+
+import { describe, it, expect, beforeEach, afterEach } from "vitest";
+import { mkdirSync, writeFileSync, rmSync } from "node:fs";
+import { join } from "node:path";
+import { tmpdir } from "node:os";
+
+import {
+  detectTexEngine,
+  discoverMainFile,
+  parseTexErrors,
+} from "../src/tex_support";
+
+// ── Fixtures ────────────────────────────────────────────────────────────────
+
+let testDir: string;
+
+beforeEach(() => {
+  testDir = join(tmpdir(), `amicode-tex-test-${Date.now()}-${Math.random().toString(36).slice(2)}`);
+  mkdirSync(testDir, { recursive: true });
+});
+
+afterEach(() => {
+  rmSync(testDir, { recursive: true, force: true });
+});
+
+function touch(relativePath: string, content = ""): void {
+  const full = join(testDir, relativePath);
+  mkdirSync(join(full, ".."), { recursive: true });
+  writeFileSync(full, content);
+}
+
+// ── detectTexEngine ─────────────────────────────────────────────────────────
+
+describe("detectTexEngine", () => {
+  it("returns an engine name or null", async () => {
+    // This test just verifies the function returns the right shape.
+    // On CI without TeX installed, it returns null; locally it may find latexmk.
+    const result = await detectTexEngine();
+    expect(result === null || typeof result === "string").toBe(true);
+  });
+
+  it("respects explicit engine override", async () => {
+    const result = await detectTexEngine("xelatex");
+    // If xelatex is on PATH, it returns "xelatex"; otherwise null
+    expect(result === null || result === "xelatex").toBe(true);
+  });
+});
+
+// ── discoverMainFile ────────────────────────────────────────────────────────
+
+describe("discoverMainFile", () => {
+  it("finds a file with \\documentclass", () => {
+    touch("paper/main.tex", "\\documentclass{article}\n\\begin{document}\nHello\n\\end{document}");
+    touch("paper/refs.bib", "@article{foo}");
+    touch("paper/chapter.tex", "\\section{Intro}");
+
+    const result = discoverMainFile(join(testDir, "paper"));
+    expect(result).toBe("main.tex");
+  });
+
+  it("returns null when no \\documentclass is found", () => {
+    touch("paper/chapter.tex", "\\section{Intro}");
+    touch("paper/refs.bib", "@article{foo}");
+
+    const result = discoverMainFile(join(testDir, "paper"));
+    expect(result).toBeNull();
+  });
+
+  it("handles empty directory", () => {
+    mkdirSync(join(testDir, "empty"), { recursive: true });
+    const result = discoverMainFile(join(testDir, "empty"));
+    expect(result).toBeNull();
+  });
+
+  it("handles non-existent directory", () => {
+    const result = discoverMainFile(join(testDir, "nonexistent"));
+    expect(result).toBeNull();
+  });
+
+  it("finds \\documentclass with options", () => {
+    touch("doc/thesis.tex", "\\documentclass[12pt,a4paper]{report}\n\\begin{document}");
+
+    const result = discoverMainFile(join(testDir, "doc"));
+    expect(result).toBe("thesis.tex");
+  });
+
+  it("picks the first .tex with \\documentclass when multiple exist", () => {
+    touch("a.tex", "\\documentclass{article}");
+    touch("b.tex", "\\documentclass{book}");
+
+    const result = discoverMainFile(testDir);
+    // Should return one of them (alphabetical order expected)
+    expect(result === "a.tex" || result === "b.tex").toBe(true);
+  });
+});
+
+// ── parseTexErrors ──────────────────────────────────────────────────────────
+
+describe("parseTexErrors", () => {
+  it("extracts error with file and line", () => {
+    const log = `
+This is pdfTeX, Version 3.14159265
+./main.tex:10: Undefined control sequence.
+l.10 \\foobar
+`;
+    const errors = parseTexErrors(log);
+    expect(errors.length).toBeGreaterThan(0);
+    expect(errors[0].line).toBe(10);
+    expect(errors[0].message).toContain("Undefined control sequence");
+  });
+
+  it("extracts ! errors from log", () => {
+    const log = `
+This is pdfTeX
+! Missing $ inserted.
+<inserted text> 
+                $
+l.42 some text
+`;
+    const errors = parseTexErrors(log);
+    expect(errors.length).toBeGreaterThan(0);
+    expect(errors.some((e) => e.message.includes("Missing $ inserted"))).toBe(true);
+  });
+
+  it("returns empty array for clean log", () => {
+    const log = `
+This is pdfTeX
+Output written on main.pdf (1 page, 12345 bytes).
+Transcript written on main.log.
+`;
+    const errors = parseTexErrors(log);
+    expect(errors).toEqual([]);
+  });
+
+  it("handles empty string", () => {
+    expect(parseTexErrors("")).toEqual([]);
+  });
+});