fix(runtime): seed the model when a buffer read falls back to the pane

With no host model, a terminal buffer read answered with the desktop
pane's screen at the pane's size. The phone's resize restream and
pending-output recovery read through it, so a hidden pane could still
hand the phone a desktop-sized screen.

The fallback now seeds the model from that screen onto the PTY grid and
answers from the model, unless output landed during the read. The
desktop's own hidden-output recovery keeps the raw renderer fallback.

Claude-Session: lane-host-hydrate

src/main/runtime/orca-runtime-serialize-terminal-buffer-from-available-state.ts

@@ -23,7 +23,9 @@ export class OrcaRuntimeWithSerializeTerminalBufferFromAvailableState extends Or
     kittyKeyboardFlags?: number
     terminalOwner?: 'shell'
   } | null> {
-    const restoredSnapshot = await this.serializePreferredRestoredTerminalBuffer(ptyId, opts)
+    const restoredSnapshot = await this.serializePreferredRestoredTerminalBuffer(ptyId, opts, {
+      seedModelFromRenderer: true
+    })
     if (restoredSnapshot) {
       return restoredSnapshot
     }
@@ -32,7 +34,7 @@ export class OrcaRuntimeWithSerializeTerminalBufferFromAvailableState extends Or
       return headlessSnapshot
     }
 
-    const rendererSnapshot = await this.serializeRendererTerminalBuffer(ptyId, opts)
+    const rendererSnapshot = await this.serializeRendererScreenOntoModel(ptyId, opts)
     if (!rendererSnapshot) {
       return this.serializeProviderTerminalBuffer(ptyId, opts)
     }
@@ -51,7 +53,8 @@ export class OrcaRuntimeWithSerializeTerminalBufferFromAvailableState extends Or
 
   protected async serializePreferredRestoredTerminalBuffer(
     ptyId: string,
-    opts: { scrollbackRows?: number } = {}
+    opts: { scrollbackRows?: number } = {},
+    fallback: { seedModelFromRenderer?: boolean } = {}
   ) {
     if (!this.providerSnapshotPreferredPtys.has(ptyId)) {
       return null
@@ -59,10 +62,27 @@ export class OrcaRuntimeWithSerializeTerminalBufferFromAvailableState extends Or
     // Pre-attach bytes are only a suffix; older providers can fall back to the renderer.
     return (
       (await this.serializeProviderTerminalBuffer(ptyId, opts)) ??
-      (await this.serializeRendererTerminalBuffer(ptyId, opts))
+      (await (fallback.seedModelFromRenderer
+        ? this.serializeRendererScreenOntoModel(ptyId, opts)
+        : this.serializeRendererTerminalBuffer(ptyId, opts)))
     )
   }
 
+  // Why: a pane answers at its own size; seed the model onto the PTY grid and serve that instead.
+  protected async serializeRendererScreenOntoModel(
+    ptyId: string,
+    opts: { scrollbackRows?: number }
+  ) {
+    const outputSequence = this.getPtyOutputSequence(ptyId)
+    const screen = await this.serializeRendererTerminalBuffer(ptyId, opts)
+    // Why: output that landed during the read is in neither the screen nor a fresh model.
+    if (!screen?.data.length || this.getPtyOutputSequence(ptyId) !== outputSequence) {
+      return screen
+    }
+    await this.replaceHeadlessTerminalFromRendererSnapshotForRecovery(ptyId, screen)
+    return (await this.serializeHeadlessTerminalBuffer(ptyId, opts)) ?? screen
+  }
+
   async serializeRendererTerminalBuffer(
     ptyId: string,
     opts: { scrollbackRows?: number } = {}

src/main/runtime/orca-runtime-tests/terminal-side-effect-facts-part-02.spec.ts

@@ -52,7 +52,8 @@ describe('terminal side-effect fact channel', () => {
     runtime.ingestSyntheticTitleFrame('pty-1', '\x1b]0;⠋ Cursor Agent\x07')
 
     const snapshot = await runtime.serializeTerminalBuffer('pty-1', { scrollbackRows: 10 })
-    expect(snapshot?.source).toBe('renderer')
+    // The renderer screen is seeded into the host model, which then answers.
+    expect(snapshot?.source).toBe('headless')
     expect(snapshot?.lastTitle).toBe('⠋ Cursor Agent')
   })
 

src/main/runtime/terminal-buffer-renderer-fallback-grid.test.ts

@@ -0,0 +1,42 @@
+/**
+ * With no host model, a terminal buffer read falls back to the desktop pane. A hidden pane answers
+ * at its own size, so the read must seed the model onto the PTY grid and answer from it. This read
+ * backs the phone's resize restream and pending-output recovery.
+ */
+import { describe, expect, it } from 'vitest'
+import {
+  DESKTOP,
+  EXPECTED_PHONE_ROWS,
+  PHONE,
+  PTY_ID,
+  internals,
+  paintedRows,
+  setupPhoneSubscribe
+} from './mobile-phone-subscribe-test-fixture'
+
+async function readOnPhoneGrid(opts: { providerPreferred: boolean }) {
+  const { runtime, sizes } = setupPhoneSubscribe({ paneMounted: true })
+  sizes.set(PTY_ID, { ...PHONE })
+  if (opts.providerPreferred) {
+    internals(runtime).providerSnapshotPreferredPtys.add(PTY_ID)
+  }
+  const snapshot = await runtime.serializeTerminalBuffer(PTY_ID, { scrollbackRows: 100 })
+  return { runtime, snapshot }
+}
+
+describe('terminal buffer read with no host model and a desktop-sized pane', () => {
+  it('answers from a model seeded onto the PTY grid', async () => {
+    const { runtime, snapshot } = await readOnPhoneGrid({ providerPreferred: false })
+
+    expect(snapshot).toMatchObject({ source: 'headless', ...PHONE })
+    expect(snapshot && (await paintedRows(snapshot)).slice(0, 4)).toEqual(EXPECTED_PHONE_ROWS)
+    expect(runtime.hasHeadlessTerminalState(PTY_ID)).toBe(true)
+  })
+
+  it('answers from the model when a restored snapshot is preferred but the provider has none', async () => {
+    const { snapshot } = await readOnPhoneGrid({ providerPreferred: true })
+
+    expect(snapshot).toMatchObject({ source: 'headless', ...PHONE })
+    expect(snapshot?.cols).not.toBe(DESKTOP.cols)
+  })
+})