diff --git a/packages/app-bundle/manifest.json b/packages/app-bundle/manifest.json
index 8e65c7f3..c635e624 100644
--- a/packages/app-bundle/manifest.json
+++ b/packages/app-bundle/manifest.json
@@ -216,7 +216,7 @@
     "packages/app/src/pages/new-session-landing.ts": "528d27cd5d441b521674328fb7812fb2acf77233e9e436d081c98ce611e8b268",
     "packages/app/src/pages/new-session.tsx": "c060bbb15569b6da2f67146e6af0879ccb5444345df03dbc2f9b39cb98b9db78",
     "packages/app/src/pages/overlay-content-hash.test.ts": "aa208098213522dcde42434408afe9c8641fad663f44a58c316922dbd0da2f5c",
-    "packages/app/src/pages/session.tsx": "e502d2274c351612aacbed4dbee49e8692da1fb6b3411fbd1491499737772a39",
+    "packages/app/src/pages/session.tsx": "a76358b41641c2568b0904b4260f9d0e0b5747424751859e48957a5b32c46d67",
     "packages/app/src/utils/amicode-bridge.ts": "5104a04c7822f80dc0c564619e7dd2d850ba50035dbc86ea875604ecd97df05f",
     "packages/app/src/utils/amicode-bug-report.test.ts": "b1bbf49230ff3aa6d1a43ffa9165ba5a84ca4ee18a6d49f52ee5cd887c3e6444",
     "packages/app/src/utils/amicode-bug-report.ts": "d55d9cecfe17719c0d4a0ca498345c7eff6fca1de6b645e4bc3fecb40f2f4645",
@@ -692,7 +692,7 @@
     "packages/app/src/pages/session/helpers.ts": "0311f52b7cc34c2c38950512c01397e9672c89a9e61fdfa0e4696192da114f34",
     "packages/app/src/pages/session/review-tab.tsx": "3c90e6b11fad40ea19a258966c374ee12c05bd0e7891fcea561ba0b965ddc9f5",
     "packages/app/src/pages/session/session-panel-width.test.ts": "9482afba7fbce254cbbd21ef885e9e9620b981616681635376f466478f611155",
-    "packages/app/src/pages/session/session-panel-width.ts": "02ee3a02ed78db2eac47c2528055cf78aef95f389641e929ddc56c17471dcbe2",
+    "packages/app/src/pages/session/session-panel-width.ts": "654f84b2b43d9e2b0d5f021a1f859d69fe9ee579c88039a492dd3c645d087bea",
     "packages/app/src/pages/session/session-side-panel-structure.test.ts": "b2d1d007d9200d0ac4a0889e45c2dbe57a324a10cb26ae9ab8f420d3c890402b",
     "packages/app/src/pages/session/session-side-panel.tsx": "b295340d9a39ba37c9e025d6360669d2a879284c4e60df795b7902c5a4cef3fc",
     "packages/app/src/pages/session/terminal-panel-v2.tsx": "68dad9307f1d2abf3ff9248e451bd08005acf01ddc46b30a6d01b58f4a90dce0",
@@ -873,7 +873,7 @@
     "packages/ui/src/v2/components/text-shimmer-v2.tsx"
   ],
   "exceptions": [],
-  "extracted_at": "2026-09-24T04:46:38.771Z",
+  "extracted_at": "2026-09-24T20:34:57.925Z",
   "per_package": {
     "packages/app": {
       "A": 186,
diff --git a/packages/app-bundle/overlay/packages/app/src/pages/session.tsx b/packages/app-bundle/overlay/packages/app/src/pages/session.tsx
index f4b2c138..559615ae 100644
--- a/packages/app-bundle/overlay/packages/app/src/pages/session.tsx
+++ b/packages/app-bundle/overlay/packages/app/src/pages/session.tsx
@@ -78,6 +78,7 @@ import { restorePromptModel, syncPromptModel, syncSessionModel } from "@/pages/s
 import {
   clampSessionPanelWidth,
   clampWorkColumnWidth,
+  CHAT_COLLAPSE_THRESHOLD,
   SESSION_PANEL_WIDTH_MIN,
   sessionChatTakesRemainder,
   sessionPanelWidthMax,
@@ -707,9 +708,54 @@ export default function Page() {
   const chatTakesRemainder = createMemo(() =>
     sessionChatTakesRemainder({ newDesign: newSessionDesign(), columnVisible: isDesktop() && desktopV2PanelLayout().visible }),
   )
-  const workColumnWidth = createMemo(() =>
-    clampWorkColumnWidth({ width: layout.panelColumn.width(), available: sessionPanelAvailable() }),
-  )
+  const workColumnWidth = createMemo(() => {
+    // #1434: when Chat is collapsed, the Work Column fills the full row
+    if (chatCollapsed()) return sessionPanelAvailable() ?? 900
+    return clampWorkColumnWidth({ width: layout.panelColumn.width(), available: sessionPanelAvailable() })
+  })
+
+  // #1434: Work Column maximize — collapse the Chat panel to give Preview
+  // full width. The pre-maximize column width is remembered for restore.
+  const [chatCollapsed, setChatCollapsed] = createSignal(false)
+  const [preMaximizeWidth, setPreMaximizeWidth] = createSignal<number | undefined>(undefined)
+
+  const chatEffectivelyCollapsed = createMemo(() => {
+    if (chatCollapsed()) return true
+    // Also collapse when the user drags the column so wide the chat is squeezed
+    // below the threshold.
+    const available = sessionPanelAvailable()
+    if (available === undefined) return false
+    return available - workColumnWidth() < CHAT_COLLAPSE_THRESHOLD
+  })
+
+  function toggleMaximize() {
+    if (chatCollapsed()) {
+      // Restore: set column back to pre-maximize width
+      setChatCollapsed(false)
+      const restoreWidth = preMaximizeWidth() ?? WORK_COLUMN_WIDTH_MIN
+      layout.panelColumn.resize(restoreWidth)
+    } else {
+      // Maximize: remember current width, then expand column to fill
+      setPreMaximizeWidth(workColumnWidth())
+      setChatCollapsed(true)
+      const available = sessionPanelAvailable() ?? 900
+      layout.panelColumn.resize(available)
+    }
+  }
+
+  // Cmd+Shift+M (Ctrl+Shift+M on Linux/Windows) toggles maximize
+  createEffect(() => {
+    if (!newSessionDesign()) return
+    function onKeyDown(e: KeyboardEvent) {
+      if ((e.metaKey || e.ctrlKey) && e.shiftKey && e.key.toLowerCase() === "m") {
+        e.preventDefault()
+        toggleMaximize()
+      }
+    }
+    window.addEventListener("keydown", onKeyDown)
+    onCleanup(() => window.removeEventListener("keydown", onKeyDown))
+  })
+
   const sessionPanelWidth = createMemo(() => {
     if (chatTakesRemainder()) return undefined
     if (!desktopSidePanelOpen()) return "100%"
@@ -2739,6 +2785,17 @@ export default function Page() {
       >
         <Show when={!isDesktop() && !!params.id && !settings.general.newLayoutDesigns()}>{mobileTabs()}</Show>
 
+        {/* #1434: restore chevron when Chat is collapsed */}
+        <Show when={newSessionDesign() && chatEffectivelyCollapsed()}>
+          <button
+            class="shrink-0 flex items-center justify-center w-6 h-full hover:bg-background-interactive-hover rounded transition-colors"
+            title={`Show Chat (${navigator.platform.includes("Mac") ? "⌘" : "Ctrl"}⇧M)`}
+            onClick={toggleMaximize}
+          >
+            <svg width="16" height="16" viewBox="0 0 20 20" fill="none" class="text-text-dimmed"><path d="M7.5 15L12.5 10L7.5 5" stroke="currentColor" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/></svg>
+          </button>
+        </Show>
+
         <div
           classList={{
             "@container relative shrink-0 flex flex-col min-h-0 h-full transition-[width]": true,
@@ -2746,6 +2803,7 @@ export default function Page() {
             "flex-1": chatTakesRemainder(),
             "duration-[240ms] ease-[cubic-bezier(0.22,1,0.36,1)] will-change-[width] motion-reduce:transition-none":
               !size.active() && !ui.reviewSnap && !desktopInlineTerminalOnlyOpen(),
+            "!hidden": newSessionDesign() && chatEffectivelyCollapsed(),
           }}
           style={{
             width: sessionPanelWidth(),
@@ -2816,7 +2874,30 @@ export default function Page() {
                   edge), sizing layout.panelColumn within the policy bounds —
                   the chat flexes around it, never below it. */}
               <Show when={isDesktop()}>
-                <div onPointerDown={() => size.start()}>
+                <div onPointerDown={() => size.start()} onDblClick={(e) => {
+                  e.preventDefault()
+                  // #1434: double-click cycles: 50/50 → full Preview → default
+                  const available = sessionPanelAvailable() ?? 900
+                  const current = workColumnWidth()
+                  const half = Math.floor(available * 0.5)
+                  const full = available
+                  const def = WORK_COLUMN_WIDTH_MIN
+                  // Determine which snap to go to next
+                  if (Math.abs(current - half) < 20) {
+                    // Currently ~50/50 → go to full
+                    setChatCollapsed(true)
+                    setPreMaximizeWidth(half)
+                    layout.panelColumn.resize(full)
+                  } else if (current > available - CHAT_COLLAPSE_THRESHOLD) {
+                    // Currently full → go to default
+                    setChatCollapsed(false)
+                    layout.panelColumn.resize(def)
+                  } else {
+                    // Currently at some other width → go to 50/50
+                    setChatCollapsed(false)
+                    layout.panelColumn.resize(half)
+                  }
+                }}>
                   <ResizeHandle
                     direction="horizontal"
                     edge="start"
@@ -2826,9 +2907,32 @@ export default function Page() {
                     onResize={(width) => {
                       size.touch()
                       layout.panelColumn.resize(width)
+                      // #1434: if dragging pushes chat below collapse threshold,
+                      // auto-collapse it
+                      const available = sessionPanelAvailable() ?? 900
+                      if (available - width < CHAT_COLLAPSE_THRESHOLD && !chatCollapsed()) {
+                        setChatCollapsed(true)
+                        setPreMaximizeWidth(width)
+                      } else if (available - width >= CHAT_COLLAPSE_THRESHOLD && chatCollapsed()) {
+                        setChatCollapsed(false)
+                      }
                     }}
                   />
                 </div>
+                {/* #1434: Maximize/restore toggle button */}
+                <button
+                  class="absolute top-1 right-1 z-10 flex items-center justify-center w-6 h-6 rounded hover:bg-background-interactive-hover transition-colors opacity-60 hover:opacity-100"
+                  title={chatEffectivelyCollapsed()
+                    ? `Show Chat (${navigator.platform.includes("Mac") ? "⌘" : "Ctrl"}⇧M)`
+                    : `Maximize Preview (${navigator.platform.includes("Mac") ? "⌘" : "Ctrl"}⇧M)`
+                  }
+                  onClick={toggleMaximize}
+                >
+                  {chatEffectivelyCollapsed()
+                    ? <svg width="16" height="16" viewBox="0 0 20 20" fill="none" class="text-text-dimmed"><path d="M12.5 15L7.5 10L12.5 5" stroke="currentColor" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/></svg>
+                    : <svg width="16" height="16" viewBox="0 0 20 20" fill="none" class="text-text-dimmed"><path d="M7.5 15L12.5 10L7.5 5" stroke="currentColor" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/></svg>
+                  }
+                </button>
               </Show>
               <Show when={isDesktop() && (desktopV2ReviewOpen() || desktopFileTreeOpen())}>
                 <div class="min-h-0 flex-1">
diff --git a/packages/app-bundle/overlay/packages/app/src/pages/session/session-panel-width.ts b/packages/app-bundle/overlay/packages/app/src/pages/session/session-panel-width.ts
index 43191381..cce66b48 100644
--- a/packages/app-bundle/overlay/packages/app/src/pages/session/session-panel-width.ts
+++ b/packages/app-bundle/overlay/packages/app/src/pages/session/session-panel-width.ts
@@ -19,15 +19,19 @@ export function clampSessionPanelWidth(input: { width: number; available: number
 }
 
 // amicode#105: the Work Column owns a bounded width of its own. The pre-fix
-// philosophy (above) let the review pane take everything the chat left behind
+// philosophy (above) let the review pane take whatever the chat left behind
 // — a wide monitor squished the chat into the left margin. Now the column is
 // fixed-width (default 320 — DEFAULT_PANEL_COLUMN_WIDTH — user-resizable
 // within these bounds) and the CHAT is the flex remainder.
 export const WORK_COLUMN_WIDTH_MIN = 330
 
-/** The column may never take more than 60% of the measured row. */
+/** Minimum chat width before it collapses entirely (#1434). */
+export const CHAT_COLLAPSE_THRESHOLD = 200
+
+/** The column may expand to fill the full row — the chat collapses when
+ *  squeezed below CHAT_COLLAPSE_THRESHOLD (#1434). */
 export function workColumnWidthMax(available: number) {
-  return Math.max(WORK_COLUMN_WIDTH_MIN, Math.floor(available * 0.6))
+  return Math.max(WORK_COLUMN_WIDTH_MIN, available)
 }
 
 /** `available` is undefined until the layout row is first measured; render the