fix(agent-hooks): keep Antigravity status posts alive when an event carries no payload

The PowerShell post substituted `{}` for empty stdin, and the POSIX script does
the same before posting. curl forwards stdin verbatim, so a payload-less event
now arrives as `payload=""` and the shared ingest dropped it — losing the status
transition its `hook_event_name` still carried.

Accept an empty Antigravity payload as `{}` at the ingest boundary, scoped to
that source so every other agent keeps rejecting a body it cannot parse.

src/main/antigravity/windows-hook-payload-delivery.test.ts

@@ -96,7 +96,11 @@ async function startHookListener(): Promise<{
 
 type HookRun = { exitCode: number | null; stdout: string; stderr: string; timedOut: boolean }
 
-function runWrapper(wrapperPath: string, env: NodeJS.ProcessEnv): Promise<HookRun> {
+function runWrapper(
+  wrapperPath: string,
+  env: NodeJS.ProcessEnv,
+  stdinPayload: string = PAYLOAD
+): Promise<HookRun> {
   return new Promise((resolve, reject) => {
     // Why: mirror how Antigravity spawns the hook — `cmd /c <bare .cmd path>`, the exact
     // chain in the bug report's process trace.
@@ -127,7 +131,7 @@ function runWrapper(wrapperPath: string, env: NodeJS.ProcessEnv): Promise<HookRu
       // Why: curl exits once the POST is written; give the listener a beat to finish reading it.
       setTimeout(() => resolve({ exitCode, stdout, stderr, timedOut }), 250)
     })
-    child.stdin.end(Buffer.from(PAYLOAD, 'utf8'))
+    child.stdin.end(Buffer.from(stdinPayload, 'utf8'))
   })
 }
 
@@ -227,6 +231,35 @@ describe.skipIf(process.platform !== 'win32')('Antigravity Windows hook payload
     // Why: five wrapper launches plus a real install can overrun the default under load.
   }, 60_000)
 
+  // Why (#15117): Antigravity fires some events with no stdin at all. PowerShell substituted
+  // `{}` before posting; curl forwards the empty body, so prove the post still happens — the
+  // listener's matching allowance is covered in agent-hook-listener-antigravity.test.ts.
+  it('still posts a status event when the agent supplies no payload', async () => {
+    home = mkdtempSync(join(tmpdir(), 'orca-antigravity-hook-'))
+    homedirMock.mockReturnValue(home)
+    expect(new AntigravityHookService().install().state).toBe('installed')
+
+    const listener = await startHookListener()
+    server = listener.server
+    const result = await runWrapper(
+      join(home, '.orca', 'agent-hooks', 'antigravity-pre-invocation.cmd'),
+      hookEnvironment({
+        USERPROFILE: home,
+        HOME: home,
+        ORCA_AGENT_HOOK_PORT: String(listener.port),
+        ORCA_AGENT_HOOK_TOKEN: HOOK_TOKEN,
+        ORCA_PANE_KEY: PANE_KEY
+      }),
+      ''
+    )
+
+    expect(result.timedOut).toBe(false)
+    expect(result.exitCode).toBe(0)
+    expect(listener.posts).toHaveLength(1)
+    expect(listener.posts[0].payload).toBe('')
+    expect(listener.posts[0].hookEventName).toBe('PreInvocation')
+  }, 30_000)
+
   it('exits without reading stdin when the pane env is missing', async () => {
     home = mkdtempSync(join(tmpdir(), 'orca-antigravity-hook-'))
     homedirMock.mockReturnValue(home)

src/shared/agent-hook-listener-antigravity.test.ts

@@ -23,6 +23,57 @@ describe('shared agent-hook-listener', () => {
     vi.unstubAllEnvs()
   })
 
+  // Why (#15117): the Windows script posts stdin verbatim through curl, so an event that
+  // fires without a payload arrives as `payload=""` rather than the `{}` the POSIX script
+  // substitutes. Both transports must still produce the status transition.
+  it('accepts an Antigravity event whose payload arrived empty', () => {
+    const started = normalizeHookPayload(
+      state,
+      'antigravity',
+      {
+        paneKey: PANE_KEY,
+        tabId: 'tab-1',
+        worktreeId: 'wt',
+        hook_event_name: 'PreInvocation',
+        payload: ''
+      },
+      'production'
+    )
+    expect(started?.payload).toMatchObject({ state: 'working', agentType: 'antigravity' })
+  })
+
+  it('still drops an Antigravity event whose payload is malformed rather than empty', () => {
+    expect(
+      normalizeHookPayload(
+        state,
+        'antigravity',
+        {
+          paneKey: PANE_KEY,
+          hook_event_name: 'PreInvocation',
+          payload: '{"prompt":'
+        },
+        'production'
+      )
+    ).toBeNull()
+  })
+
+  // Why: the empty-payload allowance is Antigravity's documented policy, not a global one —
+  // every other source must keep rejecting a body it cannot parse.
+  it('does not extend the empty-payload allowance to other sources', () => {
+    expect(
+      normalizeHookPayload(
+        state,
+        'gemini',
+        {
+          paneKey: PANE_KEY,
+          hook_event_name: 'BeforeAgent',
+          payload: ''
+        },
+        'production'
+      )
+    ).toBeNull()
+  })
+
   it('normalizes Antigravity invocation and tool hooks', () => {
     const started = normalizeHookPayload(
       state,

src/shared/agent-hook-listener.ts

@@ -4369,6 +4369,13 @@ export function normalizeHookPayload(
   const hookPayload =
     typeof rawPayload === 'string'
       ? (() => {
+          // Why (#15117): some Antigravity events fire with no stdin at all, yet still carry a
+          // status transition in `hook_event_name`. The POSIX script maps empty input to `{}`
+          // before posting; the Windows script pipes stdin straight into curl and cannot, so
+          // accept the empty body here instead of dropping the event.
+          if (source === 'antigravity' && rawPayload.trim() === '') {
+            return {}
+          }
           try {
             return parseAgentHookJson(rawPayload)
           } catch {

src/shared/wsl-exec-mode-separator.test.ts

@@ -85,7 +85,7 @@ describe('wsl.exe mode separator', () => {
   it('sees a `--` separator split across lines by the formatter', () => {
     // Why: the guard once matched line-by-line and was blind to this exact shape,
     // which is how every multi-element argv array in this repo is formatted.
-    const formatted = ["args: [", "  '-d',", "  distro,", "  '--',", "  'bash'", "]"].join('\n')
+    const formatted = ['args: [', "  '-d',", '  distro,', "  '--',", "  'bash'", ']'].join('\n')
 
     expect(ARGV_FORM.test(codeText(formatted))).toBe(true)
   })