diff --git a/apps/desktop/e2e/correction-session-switch.spec.ts b/apps/desktop/e2e/correction-session-switch.spec.ts
index dd32caa61e71..dc435b1d5384 100644
--- a/apps/desktop/e2e/correction-session-switch.spec.ts
+++ b/apps/desktop/e2e/correction-session-switch.spec.ts
@@ -21,8 +21,16 @@ const INFERENCE_SWITCH_TRIGGER = 'E2E_INFERENCE_SWITCH_TRIGGER'
 const INFERENCE_PROMPT = `${INFERENCE_SWITCH_TRIGGER}: original inference prompt must remain singular.`
 const INFERENCE_CORRECTION = `${INFERENCE_SWITCH_TRIGGER}: correction sent while inference is live.`
 
+// Inactive tabs stay mounted under a data-pane-hidden ancestor. Match the
+// renderer's keep-alive visibility policy instead of relying on DOM order.
+const SURFACE = '[data-composer-target]:not([data-pane-hidden] [data-composer-target])'
+
+function activeSurface(page: Page) {
+  return page.locator(SURFACE).last()
+}
+
 async function send(page: Page, text: string): Promise<void> {
-  const composer = page.locator('[contenteditable="true"]').first()
+  const composer = activeSurface(page).locator('[contenteditable="true"]').first()
   await composer.waitFor({ state: 'visible', timeout: 15_000 })
   await composer.click()
   await composer.type(text, { delay: 5 })
@@ -30,8 +38,9 @@ async function send(page: Page, text: string): Promise<void> {
 }
 
 async function steer(page: Page, text: string): Promise<void> {
-  const composer = page.locator('[contenteditable="true"]').first()
-  const primary = page.locator('[data-slot="composer-root"] button[type="submit"]')
+  const surface = activeSurface(page)
+  const composer = surface.locator('[contenteditable="true"]').first()
+  const primary = surface.locator('[data-slot="composer-root"] button[type="submit"]')
 
   await composer.waitFor({ state: 'visible', timeout: 15_000 })
   await composer.click()
@@ -42,55 +51,80 @@ async function steer(page: Page, text: string): Promise<void> {
 
 async function waitForTranscriptText(page: Page, text: string): Promise<void> {
   await page.waitForFunction(
-    (expected: string) => (document.querySelector('[data-slot="aui_thread-viewport"]')?.textContent ?? '').includes(expected),
-    text,
+    ([expected, surfaceSelector]: [string, string]) => {
+      const surfaces = document.querySelectorAll(surfaceSelector)
+      const active = surfaces[surfaces.length - 1]
+
+      return (active?.querySelector('[data-slot="aui_thread-viewport"]')?.textContent ?? '').includes(expected)
+    },
+    [text, SURFACE] as [string, string],
     { timeout: 30_000 },
   )
 }
 
 async function textNodeOccurrences(page: Page, text: string): Promise<number> {
-  return page.evaluate((expected: string) => {
-    const viewport = document.querySelector('[data-slot="aui_thread-viewport"]')
-    if (!viewport) return 0
+  return page.evaluate(
+    ([expected, surfaceSelector]: [string, string]) => {
+      const surfaces = document.querySelectorAll(surfaceSelector)
+      const viewport = surfaces[surfaces.length - 1]?.querySelector('[data-slot="aui_thread-viewport"]')
+      if (!viewport) return 0
 
-    const walker = document.createTreeWalker(viewport, NodeFilter.SHOW_TEXT)
-    let count = 0
-    while (walker.nextNode()) {
-      if (walker.currentNode.textContent?.includes(expected)) {
-        count += 1
+      const walker = document.createTreeWalker(viewport, NodeFilter.SHOW_TEXT)
+      let count = 0
+      while (walker.nextNode()) {
+        if (walker.currentNode.textContent?.includes(expected)) {
+          count += 1
+        }
       }
-    }
-    return count
-  }, text)
+      return count
+    },
+    [text, SURFACE] as [string, string],
+  )
 }
 
 async function transcriptTextOrder(page: Page): Promise<string[]> {
-  return page.evaluate(() => {
-    const viewport = document.querySelector('[data-slot="aui_thread-viewport"]')
+  return page.evaluate((surfaceSelector: string) => {
+    const surfaces = document.querySelectorAll(surfaceSelector)
+    const viewport = surfaces[surfaces.length - 1]?.querySelector('[data-slot="aui_thread-viewport"]')
     if (!viewport) return []
 
     return Array.from(viewport.querySelectorAll<HTMLElement>('[data-role="message"], [data-message-id]'))
       .map(message => message.textContent?.trim() ?? '')
       .filter(Boolean)
-  })
+  }, SURFACE)
 }
 
 async function transcriptMessageOrder(page: Page): Promise<string[]> {
-  return page.evaluate(() => {
-    const viewport = document.querySelector('[data-slot="aui_thread-viewport"]')
+  return page.evaluate((surfaceSelector: string) => {
+    const surfaces = document.querySelectorAll(surfaceSelector)
+    const viewport = surfaces[surfaces.length - 1]?.querySelector('[data-slot="aui_thread-viewport"]')
     if (!viewport) return []
 
-    return Array.from(viewport.querySelectorAll<HTMLElement>('[data-role="user"], [data-role="assistant"]'))
+    return Array.from(
+      viewport.querySelectorAll<HTMLElement>('[data-role="user"], [data-role="assistant"], [data-role="system"]'),
+    )
       .map(message => message.textContent?.trim() ?? '')
       .filter(Boolean)
-  })
+  }, SURFACE)
 }
 
+/**
+ * The sidebar "+" opens a NEW TAB beside the current chat rather than
+ * replacing it, so the prior session stays mounted in its own surface. Wait
+ * for the newly-mounted surface to show an empty transcript instead of waiting
+ * for the old text to disappear from the page (it never will).
+ */
 async function openFreshDraft(page: Page, priorSessionText: string): Promise<void> {
   await page.locator('[data-slot="sidebar"] button[aria-label="New session"]').first().click()
   await page.waitForFunction(
-    (priorText: string) => !(document.querySelector('[data-slot="aui_thread-viewport"]')?.textContent ?? '').includes(priorText),
-    priorSessionText,
+    ([priorText, surfaceSelector]: [string, string]) => {
+      const surfaces = document.querySelectorAll(surfaceSelector)
+      const active = surfaces[surfaces.length - 1]
+      const transcript = active?.querySelector('[data-slot="aui_thread-viewport"]')?.textContent ?? ''
+
+      return surfaces.length > 0 && !transcript.includes(priorText)
+    },
+    [priorSessionText, SURFACE] as [string, string],
     { timeout: 15_000 },
   )
 }
@@ -116,7 +150,12 @@ async function reopenInferenceSession(page: Page): Promise<void> {
 }
 
 function relevantOrder(messages: string[]): string[] {
-  return messages.filter(message => message.includes(ORIGINAL_PROMPT) || message.includes(CORRECTION))
+  return messages.flatMap(message => {
+    if (message.includes(ORIGINAL_PROMPT)) return [ORIGINAL_PROMPT]
+    if (message.includes(CORRECTION)) return [CORRECTION]
+
+    return []
+  })
 }
 
 function steerTurnOrder(messages: string[]): string[] {
diff --git a/apps/desktop/e2e/image-attachment-resume.spec.ts b/apps/desktop/e2e/image-attachment-resume.spec.ts
index cfa9829a4e2e..a4f8da68e39d 100644
--- a/apps/desktop/e2e/image-attachment-resume.spec.ts
+++ b/apps/desktop/e2e/image-attachment-resume.spec.ts
@@ -93,28 +93,53 @@ function sessionRow(page: Page) {
   return page.locator('[data-slot="sidebar"] button').filter({ hasText: CAPTION }).first()
 }
 
+// Inactive tabs stay mounted under a data-pane-hidden ancestor. Match the
+// renderer's keep-alive visibility policy instead of relying on DOM order.
+const SURFACE = '[data-composer-target]:not([data-pane-hidden] [data-composer-target])'
+
+function activeViewportText(surfaceSelector: string): string {
+  const surfaces = document.querySelectorAll(surfaceSelector)
+
+  return surfaces[surfaces.length - 1]?.querySelector('[data-slot="aui_thread-viewport"]')?.textContent ?? ''
+}
+
 async function openSeededSession(page: Page): Promise<void> {
   const row = sessionRow(page)
   await row.waitFor({ state: 'visible', timeout: 60_000 })
   await row.click()
   await page.waitForFunction(
-    expected => (document.querySelector('[data-slot="aui_thread-viewport"]')?.textContent ?? '').includes(expected),
-    CAPTION,
+    ([expected, surfaceSelector]: [string, string]) => {
+      const surfaces = document.querySelectorAll(surfaceSelector)
+      const text = surfaces[surfaces.length - 1]?.querySelector('[data-slot="aui_thread-viewport"]')?.textContent ?? ''
+
+      return text.includes(expected)
+    },
+    [CAPTION, SURFACE] as [string, string],
     { timeout: 30_000 },
   )
 }
 
+/**
+ * The sidebar "+" opens a NEW TAB beside the current chat instead of replacing
+ * it, so the seeded session stays mounted in its own surface. Assert the new
+ * surface is empty rather than waiting for the old caption to leave the page.
+ */
 async function openNewSession(page: Page): Promise<void> {
   await page.locator('[data-slot="sidebar"] button[aria-label="New session"]').first().click()
   await page.waitForFunction(
-    expected => !(document.querySelector('[data-slot="aui_thread-viewport"]')?.textContent ?? '').includes(expected),
-    CAPTION,
+    ([expected, surfaceSelector]: [string, string]) => {
+      const surfaces = document.querySelectorAll(surfaceSelector)
+      const text = surfaces[surfaces.length - 1]?.querySelector('[data-slot="aui_thread-viewport"]')?.textContent ?? ''
+
+      return surfaces.length > 0 && !text.includes(expected)
+    },
+    [CAPTION, SURFACE] as [string, string],
     { timeout: 15_000 },
   )
 }
 
 async function transcriptText(page: Page): Promise<string> {
-  return page.evaluate(() => document.querySelector('[data-slot="aui_thread-viewport"]')?.textContent ?? '')
+  return page.evaluate(activeViewportText, SURFACE)
 }
 
 async function assertRendersThumbnail(page: Page, label: string): Promise<void> {
diff --git a/apps/desktop/e2e/warm-resume-jitter.spec.ts b/apps/desktop/e2e/warm-resume-jitter.spec.ts
index 72e71087d690..dbc0fe5dd113 100644
--- a/apps/desktop/e2e/warm-resume-jitter.spec.ts
+++ b/apps/desktop/e2e/warm-resume-jitter.spec.ts
@@ -24,6 +24,8 @@
  *    MutationObserver burst), but `$messages` was still set twice.
  *
  * The test passes when bursts === 1 AND reconciles === 0.
+ * The sidebar "+" keeps the session warm in another tab. Its reactivation
+ * follows the same contract: one additive paint and zero reconciles.
  *
  * Prerequisite: `npm run build` must have been run so dist/ exists.
  */
@@ -43,6 +45,11 @@ import { startMockServer } from './mock-server'
 import { RealSessionBuilder } from './real-session-builder'
 
 const SESSION_TITLE = 'E2E Warm Resume Jitter Test'
+
+// Inactive tabs stay mounted under a data-pane-hidden ancestor. Match the
+// renderer's keep-alive visibility policy instead of relying on DOM order.
+const SURFACE = '[data-composer-target]:not([data-pane-hidden] [data-composer-target])'
+const ALL_SURFACES = '[data-composer-target]'
 /** 32 messages (16 user/assistant pairs) — enough DOM churn for detection. */
 const MESSAGE_COUNT = 32
 /** Seeded PRNG so the generated content is deterministic across runs. */
@@ -154,15 +161,29 @@ test.afterAll(async () => {
  *   after the initial paint, catching key-based reconciles that don't
  *   add/remove nodes.
  */
-async function installRenderCounter(page: import('@playwright/test').Page): Promise<void> {
-  await page.evaluate(() => {
-    const viewport = document.querySelector('[data-slot="aui_thread-viewport"]')
+async function installRenderCounter(
+  page: import('@playwright/test').Page,
+  transcriptText?: string,
+): Promise<void> {
+  await page.evaluate(([visibleSelector, allSelector, expected]: [string, string, string | undefined]) => {
+    const surfaces = [...document.querySelectorAll(expected ? allSelector : visibleSelector)]
+    const surface = expected
+      ? surfaces.find(candidate =>
+          (candidate.querySelector('[data-slot="aui_thread-viewport"]')?.textContent ?? '').includes(expected),
+        )
+      : surfaces.at(-1)
+    const viewport = surface?.querySelector('[data-slot="aui_thread-viewport"]')
     if (!viewport) {
       throw new Error('Thread viewport not found before warm resume')
     }
 
     const state = { bursts: 0, mutations: 0, timeline: [] as number[], stopped: false, reconciles: 0 }
-    ;(window as unknown as { __RENDER_COUNT__: typeof state }).__RENDER_COUNT__ = state
+    const debugWindow = window as unknown as {
+      __RENDER_COUNT__: typeof state
+      __RENDER_VIEWPORT__: Element
+    }
+    debugWindow.__RENDER_COUNT__ = state
+    debugWindow.__RENDER_VIEWPORT__ = viewport
 
     let currentBatch = 0
     let flushTimer: ReturnType<typeof setTimeout> | null = null
@@ -224,7 +245,53 @@ async function installRenderCounter(page: import('@playwright/test').Page): Prom
         hasMessages = true
       }
     }, 2)
-  })
+  }, [SURFACE, ALL_SURFACES, transcriptText] as [string, string, string | undefined])
+}
+
+/** Wait until the ACTIVE chat surface's transcript contains `text`. */
+async function waitForActiveTranscriptText(
+  page: import('@playwright/test').Page,
+  text: string,
+  timeout = 30_000,
+): Promise<void> {
+  await page.waitForFunction(
+    ([expected, surfaceSelector]: [string, string]) => {
+      const surfaces = document.querySelectorAll(surfaceSelector)
+      const active = surfaces[surfaces.length - 1]
+
+      return (active?.querySelector('[data-slot="aui_thread-viewport"]')?.textContent ?? '').includes(expected)
+    },
+    [text, SURFACE] as [string, string],
+    { timeout },
+  )
+}
+
+async function waitForActiveTranscriptWithoutText(
+  page: import('@playwright/test').Page,
+  text: string,
+): Promise<void> {
+  await page.waitForFunction(
+    ([expected, surfaceSelector]: [string, string]) => {
+      const surfaces = document.querySelectorAll(surfaceSelector)
+      const active = surfaces[surfaces.length - 1]
+
+      return !(active?.querySelector('[data-slot="aui_thread-viewport"]')?.textContent ?? '').includes(expected)
+    },
+    [text, SURFACE] as [string, string],
+    { timeout: 15_000 },
+  )
+}
+
+/** Replace the primary surface with a draft while retaining its warm cache. */
+async function openFreshDraft(page: import('@playwright/test').Page, priorText: string): Promise<void> {
+  await page.keyboard.press(process.platform === 'darwin' ? 'Meta+N' : 'Control+N')
+  await waitForActiveTranscriptWithoutText(page, priorText)
+}
+
+/** Stack an empty tab while leaving the current transcript mounted and warm. */
+async function openNewSessionTab(page: import('@playwright/test').Page, priorText: string): Promise<void> {
+  await page.locator('[data-slot="sidebar"] button[aria-label="New session"]').first().click()
+  await waitForActiveTranscriptWithoutText(page, priorText)
 }
 
 /** Stop the render counter and return the recorded burst/reconcile counts. */
@@ -245,6 +312,30 @@ async function readRenderCount(page: import('@playwright/test').Page): Promise<{
   })
 }
 
+async function observedViewportIsActive(page: import('@playwright/test').Page): Promise<boolean> {
+  return page.evaluate((surfaceSelector: string) => {
+    const surfaces = document.querySelectorAll(surfaceSelector)
+    const activeViewport = surfaces[surfaces.length - 1]?.querySelector('[data-slot="aui_thread-viewport"]')
+    const observedViewport = (window as unknown as { __RENDER_VIEWPORT__?: Element }).__RENDER_VIEWPORT__
+
+    return activeViewport === observedViewport
+  }, SURFACE)
+}
+
+/** A kept-alive tab must become visible without rebuilding its transcript. */
+function assertNoRepaint(result: { bursts: number; mutations: number; timeline: number[]; reconciles: number } | null): void {
+  expect(result, 'MutationObserver should have recorded render data').toBeTruthy()
+  expect(
+    result!.bursts,
+    `Expected no additive render bursts for a kept-alive tab, but got ${result!.bursts}. ` +
+      `Mutation timeline: ${JSON.stringify(result!.timeline)}.`,
+  ).toBe(0)
+  expect(
+    result!.reconciles,
+    `Expected no transcript reconciles for a kept-alive tab, but got ${result!.reconciles}.`,
+  ).toBe(0)
+}
+
 /** Assert the render counter shows exactly one paint with no re-renders. */
 function assertNoJitter(result: { bursts: number; mutations: number; timeline: number[]; reconciles: number } | null): void {
   expect(result, 'MutationObserver should have recorded render data').toBeTruthy()
@@ -261,7 +352,7 @@ function assertNoJitter(result: { bursts: number; mutations: number; timeline: n
   ).toBe(0)
 }
 
-test('warm-route resume paints transcript exactly once (no jitter)', async ({}, testInfo) => {
+test('tab reactivation preserves the mounted transcript without repainting', async ({}, testInfo) => {
   const page = fixture!.page
 
   // Wait for the sidebar to populate with our seeded session.
@@ -277,63 +368,29 @@ test('warm-route resume paints transcript exactly once (no jitter)', async ({},
 
   // Wait for the transcript to appear — the first user message text confirms
   // the cold-path prefetch painted.
-  await page.waitForFunction(
-    (text: string) =>
-      document.querySelector('[data-slot="aui_thread-viewport"]')?.textContent?.includes(text) ??
-      false,
-    FIRST_USER_MSG,
-    { timeout: 30_000 },
-  )
+  await waitForActiveTranscriptText(page, FIRST_USER_MSG)
 
   // Wait for the session to fully settle (cold-path RPC + reconciliation).
   await page.waitForTimeout(2_000)
 
-  // Step 2: Navigate away to a new chat — this does NOT evict the warm cache.
-  const newSessionButton = page
-    .locator('[data-slot="sidebar"] button[aria-label="New session"]')
-    .first()
-  await newSessionButton.click()
-
-  // Wait for the new-chat empty state.
-  await page.waitForFunction(
-    (firstMsg: string) => {
-      const viewport = document.querySelector('[data-slot="aui_thread-viewport"]')
-      if (!viewport) return false
-      const text = viewport.textContent ?? ''
-      return !text.includes(firstMsg)
-    },
-    FIRST_USER_MSG,
-    { timeout: 15_000 },
-  )
-
+  // Stack a new tab, then observe the seeded transcript while it is hidden.
+  // Installing after the switch isolates reactivation from mutations caused
+  // while the new tab was being created.
+  await openNewSessionTab(page, FIRST_USER_MSG)
   await page.waitForTimeout(500)
+  await installRenderCounter(page, FIRST_USER_MSG)
 
-  // Step 3: Install render counter, click back (warm resume), wait, assert.
-  await installRenderCounter(page)
+  // Step 3: Click back and verify the same kept-alive viewport becomes active
+  // without rebuilding or reconciling its transcript.
   await sessionRow.click()
 
-  await page.waitForFunction(
-    (text: string) =>
-      document.querySelector('[data-slot="aui_thread-viewport"]')?.textContent?.includes(text) ??
-      false,
-    FIRST_USER_MSG,
-    { timeout: 30_000 },
-  )
-
-  // Wait for at least 1 burst, then settle.
-  await page.waitForFunction(
-    () => {
-      const w = window as unknown as { __RENDER_COUNT__?: { bursts: number } }
-      return Boolean(w.__RENDER_COUNT__ && w.__RENDER_COUNT__.bursts > 0)
-    },
-    undefined,
-    { timeout: 10_000 },
-  )
+  await waitForActiveTranscriptText(page, FIRST_USER_MSG)
   await page.waitForTimeout(2_000)
+  expect(await observedViewportIsActive(page), 'Reactivation should reveal the observed kept-alive viewport').toBe(true)
 
   const result = await readRenderCount(page)
   await page.screenshot({ path: testInfo.outputPath('warm-resume-idle.png') })
-  assertNoJitter(result)
+  assertNoRepaint(result)
 })
 
 test('warm-route resume after background inference completes (no jitter)', async ({}, testInfo) => {
@@ -354,13 +411,7 @@ test('warm-route resume after background inference completes (no jitter)', async
 
   // Step 1: Cold resume — populate the warm cache.
   await sessionRow.click()
-  await page.waitForFunction(
-    (text: string) =>
-      document.querySelector('[data-slot="aui_thread-viewport"]')?.textContent?.includes(text) ??
-      false,
-    FIRST_USER_MSG,
-    { timeout: 30_000 },
-  )
+  await waitForActiveTranscriptText(page, FIRST_USER_MSG)
   await page.waitForTimeout(2_000)
 
   // Step 2: Send a message — triggers inference via the mock server.
@@ -373,34 +424,15 @@ test('warm-route resume after background inference completes (no jitter)', async
   // Wait for the mock response to appear in the transcript, confirming
   // the turn completed and message.complete fired (which updates the warm
   // cache via updateSessionState).
-  await page.waitForFunction(
-    () => {
-      const viewport = document.querySelector('[data-slot="aui_thread-viewport"]')
-      return viewport?.textContent?.includes('mock inference server') ?? false
-    },
-    undefined,
-    { timeout: 60_000 },
-  )
+  await waitForActiveTranscriptText(page, 'mock inference server', 60_000)
   // Extra settle for message.complete → updateSessionState → cache write.
   await page.waitForTimeout(2_000)
 
   // Verify the prompt was received by the mock server.
   expect(mock.receivedPrompts).toContain(PROMPT)
 
-  // Step 3: Navigate away — the warm cache retains the updated messages.
-  const newSessionButton = page
-    .locator('[data-slot="sidebar"] button[aria-label="New session"]')
-    .first()
-  await newSessionButton.click()
-  await page.waitForFunction(
-    (prompt: string) => {
-      const viewport = document.querySelector('[data-slot="aui_thread-viewport"]')
-      if (!viewport) return false
-      return !(viewport.textContent ?? '').includes(prompt)
-    },
-    PROMPT,
-    { timeout: 15_000 },
-  )
+  // Step 3: Replace the primary chat; the warm cache retains the updated messages.
+  await openFreshDraft(page, PROMPT)
   await page.waitForTimeout(500)
 
   // Step 4: Install render counter, click back (warm resume), wait, assert.
@@ -409,13 +441,7 @@ test('warm-route resume after background inference completes (no jitter)', async
 
   // Wait for the transcript to reappear — the warm cache should already
   // have the completed turn (updated by message.complete events).
-  await page.waitForFunction(
-    (text: string) =>
-      document.querySelector('[data-slot="aui_thread-viewport"]')?.textContent?.includes(text) ??
-      false,
-    FIRST_USER_MSG,
-    { timeout: 30_000 },
-  )
+  await waitForActiveTranscriptText(page, FIRST_USER_MSG)
 
   // Wait for at least 1 burst, then settle.
   await page.waitForFunction(
diff --git a/apps/desktop/src/app/chat/session-tile-actions.ts b/apps/desktop/src/app/chat/session-tile-actions.ts
index 0a6db9733508..a189af6f6479 100644
--- a/apps/desktop/src/app/chat/session-tile-actions.ts
+++ b/apps/desktop/src/app/chat/session-tile-actions.ts
@@ -236,23 +236,6 @@ export function useSessionTileActions({ runtimeId, scope, storedSessionId }: Ses
     [listTileSession, scope.attachments.$attachments, submitPromptText]
   )
 
-  const appendSystemNote = useCallback(
-    (text: string) => {
-      update(state => ({
-        ...state,
-        messages: [
-          ...state.messages,
-          {
-            id: `system-${Date.now()}-${Math.random().toString(36).slice(2, 8)}`,
-            role: 'system',
-            parts: [textPart(text)]
-          }
-        ]
-      }))
-    },
-    [update]
-  )
-
   const cancelRun = useCallback(async () => {
     const sessionId = runtimeIdRef.current
 
@@ -283,30 +266,82 @@ export function useSessionTileActions({ runtimeId, scope, storedSessionId }: Ses
   const steerPrompt = useCallback(
     async (rawText: string): Promise<boolean> => {
       const text = rawText.trim()
+      const sessionId = runtimeIdRef.current
 
-      if (!text) {
+      if (!text || !sessionId) {
         return false
       }
 
+      const messageId = `user-${Date.now()}-${Math.random().toString(36).slice(2, 8)}`
+      const mutate = (updater: (state: ClientSessionState) => ClientSessionState) =>
+        sessionTileDelegate()?.updateSession(sessionId, updater)
+
+      // Match the primary composer: insert the correction before the active
+      // reply before awaiting the redirect RPC, whose completion can race us.
+      mutate(state => {
+        const message = {
+          id: messageId,
+          role: 'user' as const,
+          parts: [textPart(text)]
+        }
+        const streamIndex = state.streamId
+          ? state.messages.findIndex(candidate => candidate.id === state.streamId)
+          : -1
+        const lastAssistantIndex = state.messages.map(candidate => candidate.role).lastIndexOf('assistant')
+        const insertionIndex = streamIndex >= 0 ? streamIndex : lastAssistantIndex
+        const messages =
+          insertionIndex >= 0
+            ? [...state.messages.slice(0, insertionIndex), message, ...state.messages.slice(insertionIndex)]
+            : [...state.messages, message]
+
+        return { ...state, messages }
+      })
+
+      const discardOptimisticMessage = () =>
+        mutate(state => ({
+          ...state,
+          messages: state.messages.filter(message => message.id !== messageId)
+        }))
+
+      const moveOptimisticMessageToEnd = () =>
+        mutate(state => {
+          const message = state.messages.find(candidate => candidate.id === messageId)
+
+          return message
+            ? { ...state, messages: [...state.messages.filter(candidate => candidate.id !== messageId), message] }
+            : state
+        })
+
       try {
-        const result = await requestGateway<{ status?: string }>('session.steer', {
-          session_id: runtimeIdRef.current,
+        const result = await requestGateway<{ status?: string }>('session.redirect', {
+          session_id: sessionId,
           text
         })
 
-        if (result?.status === 'queued') {
+        if (result?.status === 'redirected') {
+          triggerHaptic('submit')
+
+          return true
+        }
+
+        if (result?.status === 'queued') {
+          moveOptimisticMessageToEnd()
           triggerHaptic('submit')
-          appendSystemNote(`steer:${text}`)
 
           return true
         }
       } catch {
+        discardOptimisticMessage()
         // Swallow — the caller queues the text so nothing is lost.
+
+        return false
       }
 
+      discardOptimisticMessage()
+
       return false
     },
-    [appendSystemNote, requestGateway]
+    [requestGateway]
   )
 
   // Rewind primitive (interrupt-first for live turns, busy-retry) — shared with
diff --git a/apps/desktop/src/app/contrib/wiring.tsx b/apps/desktop/src/app/contrib/wiring.tsx
index d00bd646c1cf..a182ae68c3da 100644
--- a/apps/desktop/src/app/contrib/wiring.tsx
+++ b/apps/desktop/src/app/contrib/wiring.tsx
@@ -89,7 +89,7 @@ import { useRouteResume } from '../session/hooks/use-route-resume'
 import { useSessionActions } from '../session/hooks/use-session-actions'
 import { useSessionListActions } from '../session/hooks/use-session-list-actions'
 import { useSessionStateCache } from '../session/hooks/use-session-state-cache'
-import { startWorkspaceSession } from '../session/workspace-session-target'
+import { newSessionOpensTab, startWorkspaceSession } from '../session/workspace-session-target'
 import { useOverlayRouting } from '../shell/hooks/use-overlay-routing'
 import { useWindowControlsOverlayWidth } from '../shell/hooks/use-window-controls-overlay-width'
 import { titlebarControlsPosition } from '../shell/titlebar'
@@ -481,11 +481,22 @@ export function ContribWiring({ children }: { children: ReactNode }) {
     void refreshActiveProfile()
   }, [activeGatewayProfile, refreshCurrentModel, refreshHermesConfig])
 
-  // New session anchored to a workspace (sidebar "+" on a project/worktree).
-  // Seeds cwd + branch from the clicked workspace; an explicit worktree path
-  // also drills the sidebar into that project so the new lane is visible.
+  // New session anchored to a workspace. Seeds cwd + branch from the clicked
+  // workspace; an explicit worktree path also drills the sidebar into that
+  // project so the new lane is visible.
+  //
+  // `openTab` is the sidebar "+" behavior: once a chat is loaded, stack a new
+  // tab instead of replacing it (see newSessionOpensTab). The composer's
+  // "branch off into a new worktree" flow keeps the fresh-draft path — it
+  // prefills the MAIN composer right after, so it has to own that surface.
   const startSessionInWorkspace = useCallback(
-    (path: null | string) => {
+    (path: null | string, options?: { openTab?: boolean }) => {
+      if (options?.openTab && newSessionOpensTab(activeSessionIdRef.current, $selectedStoredSessionId.get())) {
+        void openNewSessionTile('center', { cwd: path, listed: false })
+
+        return
+      }
+
       startWorkspaceSession({
         activeSessionIdRef,
         followActiveSessionCwd,
@@ -495,7 +506,7 @@ export function ContribWiring({ children }: { children: ReactNode }) {
         startFreshSessionDraft
       })
     },
-    [activeSessionIdRef, requestGateway, startFreshSessionDraft]
+    [activeSessionIdRef, openNewSessionTile, requestGateway, startFreshSessionDraft]
   )
 
   // Composer "branch off into a new worktree": open a fresh session anchored
@@ -791,7 +802,7 @@ export function ContribWiring({ children }: { children: ReactNode }) {
       navigate(CRON_ROUTE)
     },
     onNavigate: selectSidebarItem,
-    onNewSessionInWorkspace: startSessionInWorkspace,
+    onNewSessionInWorkspace: path => startSessionInWorkspace(path, { openTab: true }),
     onNewSessionSplit: dir => void openNewSessionTile(dir),
     onPasteClipboardImage: opts => composer.pasteClipboardImage(opts),
     onPickFiles: () => void composer.pickContextPaths('file'),
diff --git a/apps/desktop/src/app/session/hooks/use-session-actions/index.ts b/apps/desktop/src/app/session/hooks/use-session-actions/index.ts
index 2ef5dfe9aadf..b0202e722a4d 100644
--- a/apps/desktop/src/app/session/hooks/use-session-actions/index.ts
+++ b/apps/desktop/src/app/session/hooks/use-session-actions/index.ts
@@ -476,13 +476,14 @@ export function useSessionActions({
    *  list (Cursor-style draft tab); it surfaces on the next refresh once the
    *  first message persists a turn. "Open in split" keeps the listed behavior. */
   const openNewSessionTile = useCallback(
-    async (dir: TileDock = 'right', options?: { listed?: boolean }) => {
+    async (dir: TileDock = 'right', options?: { cwd?: null | string; listed?: boolean }) => {
       const listed = options?.listed ?? true
 
       try {
-        // Fresh tile → the resolved new-session cwd (project/default), not the
-        // primary composer's live cwd.
-        const params = await desktopSessionCreateParams(resolveNewSessionCwd().trim())
+        // Fresh tile → the caller's workspace when one was named (the sidebar
+        // "+" on a project/worktree lane), else the resolved new-session cwd
+        // (project/default) — never the primary composer's live cwd.
+        const params = await desktopSessionCreateParams((options?.cwd || resolveNewSessionCwd()).trim())
         const created = await requestGateway<SessionCreateResponse>('session.create', params)
         const stored = created.stored_session_id
 
diff --git a/apps/desktop/src/app/session/workspace-session-target.test.ts b/apps/desktop/src/app/session/workspace-session-target.test.ts
index 3a83f605a321..614227585c05 100644
--- a/apps/desktop/src/app/session/workspace-session-target.test.ts
+++ b/apps/desktop/src/app/session/workspace-session-target.test.ts
@@ -9,7 +9,7 @@ import {
   setNewChatWorkspaceTarget
 } from '@/store/session'
 
-import { startWorkspaceSession } from './workspace-session-target'
+import { newSessionOpensTab, startWorkspaceSession } from './workspace-session-target'
 
 function deferred<T>() {
   let resolve!: (value: T) => void
@@ -21,6 +21,29 @@ function deferred<T>() {
   return { promise, resolve }
 }
 
+/**
+ * The sidebar "+" is a create affordance, not a discard one: with a chat
+ * already loaded it must stack a tab (⌘T) rather than replace the surface
+ * (⌘N), which would throw away a conversation that may still be mid-turn.
+ */
+describe('newSessionOpensTab', () => {
+  it('opens a tab once a conversation is on screen', () => {
+    expect(newSessionOpensTab('runtime-a', 'stored-a')).toBe(true)
+  })
+
+  it('opens a tab for a live runtime whose stored id has not landed yet', () => {
+    expect(newSessionOpensTab('runtime-a', null)).toBe(true)
+  })
+
+  it('opens a tab for a selected session still resuming into a runtime', () => {
+    expect(newSessionOpensTab(null, 'stored-a')).toBe(true)
+  })
+
+  it('replaces the empty surface when nothing is open', () => {
+    expect(newSessionOpensTab(null, null)).toBe(false)
+  })
+})
+
 describe('startWorkspaceSession', () => {
   afterEach(() => {
     setCurrentBranch('')
diff --git a/apps/desktop/src/app/session/workspace-session-target.ts b/apps/desktop/src/app/session/workspace-session-target.ts
index da5028502a11..9a87d95c0095 100644
--- a/apps/desktop/src/app/session/workspace-session-target.ts
+++ b/apps/desktop/src/app/session/workspace-session-target.ts
@@ -17,6 +17,19 @@ interface WorkspaceSessionOptions {
   startFreshSessionDraft: (options?: { workspaceTarget: string }) => void
 }
 
+/**
+ * Should the sidebar "+" open a NEW TAB rather than replace what's on screen?
+ *
+ * "+" is a create affordance, never a discard one. Once a conversation is
+ * loaded, replacing it with a blank draft would throw away a chat that may
+ * still be mid-turn, so the button stacks a tab beside it (⌘T) instead of
+ * taking over the surface (⌘N). With nothing open there is no tab worth
+ * preserving and the cheaper fresh-draft path applies.
+ */
+export function newSessionOpensTab(activeSessionId: null | string, selectedStoredSessionId: null | string): boolean {
+  return Boolean(activeSessionId || selectedStoredSessionId)
+}
+
 export function startWorkspaceSession({
   activeSessionIdRef,
   followActiveSessionCwd: followCwd = followActiveSessionCwd,