diff --git a/src/main/ipc/pty/delivery/attached-pty-size.test.ts b/src/main/ipc/pty/delivery/attached-pty-size.test.ts
index 75c3c45d99f..c117e3c30ef 100644
--- a/src/main/ipc/pty/delivery/attached-pty-size.test.ts
+++ b/src/main/ipc/pty/delivery/attached-pty-size.test.ts
@@ -98,6 +98,16 @@ describe('resolveCommittedPtySize', () => {
     ).toEqual(CACHED)
   })
 
+  it('rejects a non-integer provider grid as unproven', () => {
+    expect(
+      resolveCommittedPtySize({
+        result: { isReattach: true, snapshotCols: 120.5, snapshotRows: 40 },
+        requested: REQUESTED,
+        cachedBeforeAttach: CACHED
+      })
+    ).toEqual(CACHED)
+  })
+
   it('takes the request only when nothing better exists', () => {
     expect(
       resolveCommittedPtySize({
diff --git a/src/main/ipc/pty/delivery/attached-pty-size.ts b/src/main/ipc/pty/delivery/attached-pty-size.ts
index c799dd74be3..d16f560a9e9 100644
--- a/src/main/ipc/pty/delivery/attached-pty-size.ts
+++ b/src/main/ipc/pty/delivery/attached-pty-size.ts
@@ -6,8 +6,8 @@ export type PtyGrid = { cols: number; rows: number }
 function positiveGrid(cols: unknown, rows: unknown): PtyGrid | undefined {
   return typeof cols === 'number' &&
     typeof rows === 'number' &&
-    Number.isFinite(cols) &&
-    Number.isFinite(rows) &&
+    Number.isInteger(cols) &&
+    Number.isInteger(rows) &&
     cols > 0 &&
     rows > 0
     ? { cols, rows }
diff --git a/src/main/ipc/pty/runtime/spawn-commit-pty-size.test.ts b/src/main/ipc/pty/runtime/spawn-commit-pty-size.test.ts
new file mode 100644
index 00000000000..128ccb51021
--- /dev/null
+++ b/src/main/ipc/pty/runtime/spawn-commit-pty-size.test.ts
@@ -0,0 +1,56 @@
+import { afterEach, describe, expect, it, vi } from 'vitest'
+import { ptySizes } from '../delivery/visibility-state'
+import { commitRuntimePtySpawn } from './spawn-commit'
+import { createRuntimePtySpawnState, type RuntimePtySpawnArgs } from './spawn-state'
+import type { PtyRuntimeControllerDeps } from './controller-deps'
+
+const PTY_ID = 'orca-pty-adopted'
+const LIVE_GRID = { cols: 211, rows: 57 }
+
+function makeRuntime() {
+  return {
+    registerPreAllocatedHandleForPty: vi.fn(),
+    registerPty: vi.fn(),
+    reflowHeadlessTerminalToPtyGrid: vi.fn(),
+    seedHeadlessTerminal: vi.fn(),
+    noteTerminalSpawnCommand: vi.fn()
+  }
+}
+
+describe('runtime spawn commit: adopted agent-session claim', () => {
+  afterEach(() => {
+    ptySizes.delete(PTY_ID)
+  })
+
+  it('commits the live grid from the adoption reply before the early return', async () => {
+    const runtime = makeRuntime()
+    const deps = { runtime, store: undefined, options: {} } as unknown as PtyRuntimeControllerDeps
+    const args = { cols: 120, rows: 40, worktreeId: 'wt-1' } as unknown as RuntimePtySpawnArgs
+    const ctx = createRuntimePtySpawnState(deps, args)
+    ctx.result = {
+      id: PTY_ID,
+      isReattach: true,
+      snapshotCols: LIVE_GRID.cols,
+      snapshotRows: LIVE_GRID.rows,
+      agentSessionEnsure: {
+        disposition: 'adopted',
+        owner: {
+          claim: { kind: 'terminal' },
+          generation: 'g1',
+          phase: 'live',
+          ptyId: PTY_ID,
+          surface: { worktreeId: 'wt-1', tabId: 'tab-1', leafId: 'leaf-1', terminalHandle: 'h1' }
+        }
+      }
+    } as unknown as typeof ctx.result
+
+    await commitRuntimePtySpawn(ctx)
+
+    expect(ptySizes.get(PTY_ID)).toEqual(LIVE_GRID)
+    expect(runtime.reflowHeadlessTerminalToPtyGrid).toHaveBeenCalledWith(
+      PTY_ID,
+      LIVE_GRID.cols,
+      LIVE_GRID.rows
+    )
+  })
+})
diff --git a/src/main/ipc/pty/runtime/spawn-commit-pty-size.ts b/src/main/ipc/pty/runtime/spawn-commit-pty-size.ts
new file mode 100644
index 00000000000..a11bdccae15
--- /dev/null
+++ b/src/main/ipc/pty/runtime/spawn-commit-pty-size.ts
@@ -0,0 +1,18 @@
+import { commitAttachedPtySize } from '../delivery/attached-pty-size'
+import type { RuntimePtySpawnState } from './spawn-state'
+
+/** Record the settled grid for a runtime-path spawn; `result` is passed explicitly because the
+ *  adopted-claim branch commits with `isReattach` forced on before it returns early. */
+export function commitRuntimePtySize(
+  ctx: RuntimePtySpawnState,
+  result: RuntimePtySpawnState['result']
+): void {
+  commitAttachedPtySize({
+    result,
+    requested: { cols: ctx.args.cols, rows: ctx.args.rows },
+    cachedBeforeAttach: ctx.sessionSizeBeforeAttach,
+    reflowHeadlessTerminalToPtyGrid: ctx.deps.runtime?.reflowHeadlessTerminalToPtyGrid?.bind(
+      ctx.deps.runtime
+    )
+  })
+}
diff --git a/src/main/ipc/pty/runtime/spawn-commit.ts b/src/main/ipc/pty/runtime/spawn-commit.ts
index 1fb95236664..94af728fe12 100644
--- a/src/main/ipc/pty/runtime/spawn-commit.ts
+++ b/src/main/ipc/pty/runtime/spawn-commit.ts
@@ -1,7 +1,7 @@
 import { isValidTerminalTabId } from '../../../../shared/terminal-tab-id'
 import { ptyOwnership, ptyIncarnationById, deletePtyOwnership } from '../provider/ownership-state'
 import { ptySizes } from '../delivery/visibility-state'
-import { commitAttachedPtySize } from '../delivery/attached-pty-size'
+import { commitRuntimePtySize } from './spawn-commit-pty-size'
 import {
   shouldSkipCodexHomeEnvForWindowsShell,
   recordCodexPaneAccountForSpawn,
@@ -87,6 +87,9 @@ export async function commitRuntimePtySpawn(ctx: RuntimePtySpawnState) {
         ...(ctx.env ? { launchEnv: ctx.env } : {})
       })
     }
+    // Why: an adoption attaches to a live session too, and this branch returns before the
+    // normal commit site; without this the cache keeps whatever the caller requested.
+    commitRuntimePtySize(ctx, { ...ctx.result, isReattach: true })
     // Why: the adopted branch returns before the normal settle site, so the
     // reservation must be resolved here or every later spawn for this pane
     // awaits a promise that never settles.
@@ -126,14 +129,7 @@ export async function commitRuntimePtySpawn(ctx: RuntimePtySpawnState) {
   if (!ctx.hostSessionBinding) {
     persistSshLease()
   }
-  commitAttachedPtySize({
-    result: ctx.result,
-    requested: { cols: args.cols, rows: args.rows },
-    cachedBeforeAttach: ctx.sessionSizeBeforeAttach,
-    reflowHeadlessTerminalToPtyGrid: ctx.deps.runtime?.reflowHeadlessTerminalToPtyGrid?.bind(
-      ctx.deps.runtime
-    )
-  })
+  commitRuntimePtySize(ctx, ctx.result)
   if (ctx.effectiveSessionAppId !== undefined && ctx.effectiveSessionAppId !== ctx.result.id) {
     ptySizes.delete(ctx.effectiveSessionAppId)
   }