diff --git a/config/tsconfig.cli.json b/config/tsconfig.cli.json
index 903562b67ed..2ff9a26c569 100644
--- a/config/tsconfig.cli.json
+++ b/config/tsconfig.cli.json
@@ -103,6 +103,7 @@
     "../src/main/amp/managed-plugin-install-status.ts",
     "../src/main/antigravity/hook-events.ts",
     "../src/main/antigravity/hook-script.ts",
+    "../src/main/antigravity/windows-hook-json-post.ts",
     "../src/main/antigravity/hook-service.ts",
     "../src/main/antigravity/hooks-json-bundle.ts",
     "../src/main/claude/hook-settings.ts",
diff --git a/src/main/agent-hooks/managed-hook-stdin-lifecycle.test.ts b/src/main/agent-hooks/managed-hook-stdin-lifecycle.test.ts
index ff7602b0689..61ff977e558 100644
--- a/src/main/agent-hooks/managed-hook-stdin-lifecycle.test.ts
+++ b/src/main/agent-hooks/managed-hook-stdin-lifecycle.test.ts
@@ -300,6 +300,11 @@ describe('Windows managed hook stdin structure', () => {
         expect(script, `${fileName} no ORCA_* guard may route to the more.com drain`).not.toMatch(
           /ORCA_[A-Z_]+.*goto :?orca_agent_hook_drain_stdin/
         )
+        if (fileName === 'antigravity-hook.cmd') {
+          expect(script).not.toContain('more.com')
+          expect(script).toContain('antigravity-hook-post.cjs')
+          continue
+        }
         // Why: the epilogue stays shared — claude-hook-impl.cmd still jumps to it from the
         // Devin-imports-.claude skip, which now sits below these guards.
         expect(script, `${fileName} drain epilogue`).toContain(
diff --git a/src/main/agent-hooks/windows-hook-post-interpreter.test.ts b/src/main/agent-hooks/windows-hook-post-interpreter.test.ts
index 59a409f82d9..4d69b514ce8 100644
--- a/src/main/agent-hooks/windows-hook-post-interpreter.test.ts
+++ b/src/main/agent-hooks/windows-hook-post-interpreter.test.ts
@@ -1,6 +1,7 @@
 // Why (#15117): an agent holding a private copy of the shared post command missed the move to
 // curl for three months, invisible to per-agent tests. Assert the invariant across every agent
-// at once: a managed Windows .cmd hook posts through curl.exe and spawns no interpreter.
+// at once: EOF-based managed Windows .cmd hooks post through curl.exe.
+// Antigravity keeps stdin open and instead tests its owned bounded Node reader separately.
 // Generated under a mocked win32 platform, not executed, so the POSIX CI legs guard it too.
 import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
 import { mkdtempSync, readFileSync, readdirSync, rmSync } from 'node:fs'
@@ -33,7 +34,6 @@ vi.mock('os', async (importOriginal) => {
   }
 })
 
-import { AntigravityHookService } from '../antigravity/hook-service'
 import { ClaudeHookService } from '../claude/hook-service'
 import { CodexHookService } from '../codex/hook-service'
 import { CommandCodeHookService } from '../command-code/hook-service'
@@ -48,7 +48,6 @@ import { openClaudeHookService } from '../openclaude/hook-service'
 // `.ps1` — PowerShell is its interpreter, not a child process it spawns per event — and Kimi's
 // is a Git Bash `.sh`, so neither is subject to this invariant.
 const BATCH_SCRIPT_INSTALLERS = [
-  { agent: 'antigravity', install: () => new AntigravityHookService().install() },
   { agent: 'claude', install: () => new ClaudeHookService().install() },
   { agent: 'openclaude', install: () => openClaudeHookService.install() },
   { agent: 'codex', install: () => new CodexHookService().install() },
diff --git a/src/main/antigravity/hook-script.ts b/src/main/antigravity/hook-script.ts
index 086fc4ede63..3e5767a9726 100644
--- a/src/main/antigravity/hook-script.ts
+++ b/src/main/antigravity/hook-script.ts
@@ -2,21 +2,14 @@ import {
   buildPosixHookPayloadCapture,
   POSIX_HOOK_JSON_STDIN,
   buildPosixHookSpoolLines,
-  buildWindowsHookEnvironmentGuardLines,
-  buildWindowsHookStdinDrainEpilogue,
-  WINDOWS_HOOK_STDIN_DRAIN_COMMAND
+  buildWindowsHookEnvironmentGuardLines
 } from '../agent-hooks/hook-stdin-contract'
-import { buildWindowsAgentHookPostCommand } from '../agent-hooks/installer-utils'
 import { ANTIGRAVITY_PRE_TOOL_USE_DECISION } from './hook-events'
 
-// Why (#15117): PowerShell cost ~300ms of startup per event, which is what made the console
-// the agent allocates for each hook last long enough to see.
-const WINDOWS_ANTIGRAVITY_HOOK_POST_COMMAND = buildWindowsAgentHookPostCommand('antigravity', [
-  // Why: Antigravity alone takes its event name from the wrapper's env, not the piped payload.
-  '  --data-urlencode "hook_event_name=%ORCA_ANTIGRAVITY_EVENT%" ^'
-])
-
-export function getManagedScript(target: 'local' | 'posix' = 'local'): string {
+export function getManagedScript(
+  target: 'local' | 'posix' = 'local',
+  windowsRuntimePath = process.execPath
+): string {
   if (target === 'local' && process.platform === 'win32') {
     return [
       '@echo off',
@@ -32,9 +25,11 @@ export function getManagedScript(target: 'local' | 'posix' = 'local'): string {
       ')',
       'if defined ORCA_AGENT_HOOK_ENDPOINT if exist "%ORCA_AGENT_HOOK_ENDPOINT%" call "%ORCA_AGENT_HOOK_ENDPOINT%" 2>nul',
       ...buildWindowsHookEnvironmentGuardLines(),
-      WINDOWS_ANTIGRAVITY_HOOK_POST_COMMAND,
+      // The runtime path is fixed at installation; hook payloads stay on stdin.
+      'set "ELECTRON_RUN_AS_NODE=1"',
+      `if not defined ORCA_AGENT_HOOK_NODE set "ORCA_AGENT_HOOK_NODE=${windowsRuntimePath.replaceAll('%', '%%')}"`,
+      '"%ORCA_AGENT_HOOK_NODE%" "%~dp0antigravity-hook-post.cjs" >nul 2>nul',
       'exit /b 0',
-      ...buildWindowsHookStdinDrainEpilogue(),
       ''
     ].join('\r\n')
   }
@@ -108,7 +103,6 @@ export function getWindowsWrapperScript(eventName: string): string {
     ')',
     // Missing-core fallbacks obey the same outside-Orca stdin guard as the core.
     ...buildWindowsHookEnvironmentGuardLines(),
-    WINDOWS_HOOK_STDIN_DRAIN_COMMAND,
     'exit /b 0',
     ''
   ].join('\r\n')
diff --git a/src/main/antigravity/hook-service.test.ts b/src/main/antigravity/hook-service.test.ts
index 0142d29faac..d682c69520d 100644
--- a/src/main/antigravity/hook-service.test.ts
+++ b/src/main/antigravity/hook-service.test.ts
@@ -1,6 +1,6 @@
 import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
 import { spawnSync } from 'node:child_process'
-import { mkdirSync, mkdtempSync, readFileSync, rmSync, writeFileSync } from 'node:fs'
+import { mkdirSync, mkdtempSync, readFileSync, existsSync, rmSync, writeFileSync } from 'node:fs'
 import { tmpdir } from 'node:os'
 import { dirname, join } from 'node:path'
 
@@ -99,12 +99,15 @@ describe('AntigravityHookService', () => {
       join(homeDir, '.orca', 'agent-hooks', ANTIGRAVITY_SCRIPT_FILE_NAME),
       'utf8'
     )
-    expect(script).toContain('/hook/antigravity')
+    expect(script).toContain(
+      process.platform === 'win32' ? 'antigravity-hook-post.cjs' : '/hook/antigravity'
+    )
     if (process.platform === 'win32') {
       expect(script).not.toContain('powershell.exe')
-      expect(script).toContain('%SystemRoot%\\System32\\curl.exe')
-      expect(script).toContain('hook_event_name=%ORCA_ANTIGRAVITY_EVENT%')
-      expect(script).toContain('--data-urlencode "payload@-"')
+      expect(script).toContain('ELECTRON_RUN_AS_NODE=1')
+      expect(
+        readFileSync(join(homeDir, '.orca', 'agent-hooks', 'antigravity-hook-post.cjs'), 'utf8')
+      ).toContain('/hook/antigravity')
       // Why (#9358/#9941): delayed expansion eats `!` out of percent-expanded curl args.
       expect(script).toContain('setlocal DisableDelayedExpansion')
     } else {
@@ -279,14 +282,57 @@ describe('AntigravityHookService', () => {
         join(homeDir, '.orca', 'agent-hooks', 'antigravity-hook.cmd'),
         'utf8'
       )
-      expect(script).toContain('/hook/antigravity')
+      expect(script).toContain('antigravity-hook-post.cjs')
       expect(script).not.toContain('powershell.exe')
-      expect(script).toContain('%SystemRoot%\\System32\\curl.exe')
-      expect(script).toContain('hook_event_name=%ORCA_ANTIGRAVITY_EVENT%')
+      expect(script).toContain('ELECTRON_RUN_AS_NODE=1')
+      expect(
+        readFileSync(join(homeDir, '.orca', 'agent-hooks', 'antigravity-hook-post.cjs'), 'utf8')
+      ).toContain('/hook/antigravity')
       expect(script).toContain('setlocal DisableDelayedExpansion')
     })
   })
 
+  it('preserves the installed core and config when publishing the Windows reader fails', () => {
+    withPlatform('win32', () => {
+      const service = new AntigravityHookService()
+      expect(service.install().state).toBe('installed')
+      const hookDir = join(homeDir, '.orca', 'agent-hooks')
+      const readerPath = join(hookDir, 'antigravity-hook-post.cjs')
+      const corePath = join(hookDir, 'antigravity-hook.cmd')
+      const configPath = join(homeDir, '.gemini', 'config', 'hooks.json')
+      writeFileSync(corePath, 'previous installed core')
+      const previousConfig = readFileSync(configPath, 'utf8')
+      rmSync(readerPath)
+      mkdirSync(readerPath)
+
+      expect(() => service.install()).toThrow()
+      expect(readFileSync(corePath, 'utf8')).toBe('previous installed core')
+      expect(readFileSync(configPath, 'utf8')).toBe(previousConfig)
+    })
+  })
+
+  it('restores the owned Windows reader and resolves the current runtime on refresh', async () => {
+    vi.spyOn(process, 'platform', 'get').mockReturnValue('win32')
+    try {
+      const service = new AntigravityHookService()
+      let runtimePath = 'C:\\Orca1\\Orca.exe'
+      service.setWindowsRuntimePathProvider(() => runtimePath)
+      const readerPath = join(homeDir, '.orca', 'agent-hooks', 'antigravity-hook-post.cjs')
+      await service.refreshManagedScripts()
+      expect(existsSync(readerPath)).toBe(false)
+      expect(service.install().state).toBe('installed')
+      rmSync(readerPath)
+      runtimePath = 'C:\\Orca2\\Orca.exe'
+      await service.refreshManagedScripts()
+      expect(readFileSync(readerPath, 'utf8')).toContain("require('node:string_decoder')")
+      expect(
+        readFileSync(join(homeDir, '.orca', 'agent-hooks', 'antigravity-hook.cmd'), 'utf8')
+      ).toContain('ORCA_AGENT_HOOK_NODE=C:\\Orca2\\Orca.exe')
+    } finally {
+      vi.restoreAllMocks()
+    }
+  })
+
   it('preserves user-authored hook bundles and entries in Orca bundle', () => {
     const configPath = join(homeDir, '.gemini', 'config', 'hooks.json')
     mkdirSync(dirname(configPath), { recursive: true })
diff --git a/src/main/antigravity/hook-service.ts b/src/main/antigravity/hook-service.ts
index 31c41d13f07..fafd9d47b22 100644
--- a/src/main/antigravity/hook-service.ts
+++ b/src/main/antigravity/hook-service.ts
@@ -16,7 +16,12 @@ import {
   writeHooksJsonRemote,
   writeManagedScriptRemote
 } from '../agent-hooks/installer-utils-remote'
-import { refreshManagedScriptIfPresent } from '../agent-hooks/managed-hook-script-refresh'
+import { WINDOWS_ANTIGRAVITY_JSON_POST_SCRIPT } from './windows-hook-json-post'
+import {
+  restoreManagedScript,
+  refreshManagedScriptIfPresent,
+  scriptStillExists
+} from '../agent-hooks/managed-hook-script-refresh'
 import {
   ANTIGRAVITY_EVENTS,
   ANTIGRAVITY_PRE_TOOL_USE_DECISION,
@@ -70,9 +75,19 @@ function getManagedCommand(scriptPath: string, event: AntigravityEvent): string
 }
 
 export class AntigravityHookService {
+  private getWindowsRuntimePath = (): string => process.execPath
+
+  setWindowsRuntimePathProvider(provider: () => string): void {
+    this.getWindowsRuntimePath = provider
+  }
+
   async refreshManagedScripts(): Promise<void> {
-    await refreshManagedScriptIfPresent(getManagedScriptPath(), getManagedScript())
-    if (process.platform === 'win32') {
+    const runtimePath = process.platform === 'win32' ? this.getWindowsRuntimePath() : undefined
+    if (process.platform === 'win32' && (await scriptStillExists(getManagedScriptPath()))) {
+      await restoreManagedScript(
+        getSharedManagedScriptPath('antigravity-hook-post.cjs'),
+        WINDOWS_ANTIGRAVITY_JSON_POST_SCRIPT
+      )
       for (const event of ANTIGRAVITY_EVENTS) {
         await refreshManagedScriptIfPresent(
           getWindowsWrapperScriptPath(event),
@@ -80,6 +95,10 @@ export class AntigravityHookService {
         )
       }
     }
+    await refreshManagedScriptIfPresent(
+      getManagedScriptPath(),
+      getManagedScript('local', runtimePath)
+    )
   }
 
   getStatus(): AgentHookInstallStatus {
@@ -157,7 +176,14 @@ export class AntigravityHookService {
       (event) => getManagedCommand(scriptPath, event),
       createAntigravityManagedCommandMatcher()
     )
-    writeManagedScript(scriptPath, getManagedScript())
+    const runtimePath = process.platform === 'win32' ? this.getWindowsRuntimePath() : undefined
+    if (process.platform === 'win32') {
+      writeManagedScript(
+        getSharedManagedScriptPath('antigravity-hook-post.cjs'),
+        WINDOWS_ANTIGRAVITY_JSON_POST_SCRIPT
+      )
+    }
+    writeManagedScript(scriptPath, getManagedScript('local', runtimePath))
     if (process.platform === 'win32') {
       // Why: Antigravity wraps hook commands in cmd.exe. Keeping event env
       // setup inside event-specific .cmd files avoids nested hooks.json quotes.
diff --git a/src/main/antigravity/windows-hook-json-post.test.ts b/src/main/antigravity/windows-hook-json-post.test.ts
new file mode 100644
index 00000000000..17cff6887fc
--- /dev/null
+++ b/src/main/antigravity/windows-hook-json-post.test.ts
@@ -0,0 +1,143 @@
+import { createServer } from 'node:http'
+import { mkdtempSync, rmSync, writeFileSync } from 'node:fs'
+import { tmpdir } from 'node:os'
+import { join } from 'node:path'
+import { afterAll, expect, it } from 'vitest'
+import { spawnProcess } from '../../shared/child-process/run-process'
+import { WINDOWS_ANTIGRAVITY_JSON_POST_SCRIPT } from './windows-hook-json-post'
+
+const directory = mkdtempSync(join(tmpdir(), 'orca-agy-json-post-'))
+const script = join(directory, 'hook.cjs')
+writeFileSync(script, WINDOWS_ANTIGRAVITY_JSON_POST_SCRIPT)
+afterAll(() => rmSync(directory, { recursive: true, force: true }))
+
+it('delivers exact split UTF-8 JSON without EOF and bounds empty or partial input', async () => {
+  const posts: URLSearchParams[] = []
+  const server = createServer((request, response) => {
+    let body = ''
+    request.setEncoding('utf8')
+    request.on('data', (chunk: string) => {
+      body += chunk
+    })
+    request.on('end', () => {
+      posts.push(new URLSearchParams(body))
+      response.end('{}')
+    })
+  })
+  await new Promise<void>((resolve) => server.listen(0, '127.0.0.1', resolve))
+  const address = server.address()
+  if (!address || typeof address === 'string') {
+    throw new Error('Missing listener')
+  }
+  const env = {
+    ...process.env,
+    ORCA_AGENT_HOOK_PORT: String(address.port),
+    ORCA_AGENT_HOOK_TOKEN: 'disposable-proof-token',
+    ORCA_PANE_KEY: 'proof!pane',
+    ORCA_ANTIGRAVITY_EVENT: 'PreInvocation'
+  }
+  const payload = JSON.stringify({
+    message: '日本語 😀 café {"quoted"} \\ tail',
+    transcript: 'x'.repeat(100_000)
+  })
+  try {
+    for (const input of [payload, '', '{"partial":', '{} trailing-data']) {
+      const child = spawnProcess({ program: process.execPath, args: [script], env })
+      child.stdin.on('error', () => {})
+      let stdout = ''
+      let stderr = ''
+      child.stdout.on('data', (chunk: Buffer) => {
+        stdout += chunk.toString()
+      })
+      child.stderr.on('data', (chunk: Buffer) => {
+        stderr += chunk.toString()
+      })
+      const timer = setTimeout(() => child.kill(), 9000)
+      const closed = new Promise<number | null>((resolve, reject) => {
+        child.once('close', resolve)
+        child.once('error', reject)
+      })
+      const before = posts.length
+      if (input) {
+        const bytes = Buffer.from(input)
+        const cut = bytes.indexOf(Buffer.from('日本語')) + 1
+        child.stdin.write(bytes.subarray(0, Math.max(1, cut)))
+        await new Promise((resolve) => setTimeout(resolve, 25))
+        child.stdin.write(bytes.subarray(Math.max(1, cut)))
+      }
+      expect(await closed).toBe(0)
+      clearTimeout(timer)
+      child.stdin.destroy()
+      expect(stdout).toBe('')
+      expect(stderr).toBe('')
+      expect(posts.slice(before)).toHaveLength(1)
+      expect(posts[before].get('payload')).toBe(input || '{}')
+      expect(posts[before].get('paneKey')).toBe('proof!pane')
+      expect(posts[before].get('hook_event_name')).toBe('PreInvocation')
+    }
+  } finally {
+    await new Promise<void>((resolve) => server.close(() => resolve()))
+  }
+}, 20_000)
+
+it('bounds oversized payloads, encoded bodies, absent endpoints and stalled HTTP', async () => {
+  let requests = 0
+  const server = createServer((request) => {
+    requests++
+    request.resume()
+  })
+  await new Promise<void>((resolve) => server.listen(0, '127.0.0.1', resolve))
+  const address = server.address()
+  if (!address || typeof address === 'string') {
+    throw new Error('Missing listener')
+  }
+  const env = {
+    ...process.env,
+    ORCA_AGENT_HOOK_PORT: String(address.port),
+    ORCA_AGENT_HOOK_TOKEN: 'disposable-proof-token',
+    ORCA_PANE_KEY: 'proof-pane'
+  }
+  try {
+    for (const payloadCase of ['oversized', 'encoded-oversized', 'no-endpoint', 'hung-http']) {
+      const before = requests
+      const child = spawnProcess({
+        program: process.execPath,
+        args: [script],
+        env: payloadCase === 'no-endpoint' ? { ...env, ORCA_AGENT_HOOK_PORT: '' } : env
+      })
+      child.stdin.on('error', () => {})
+      let output = ''
+      child.stdout.on('data', (chunk: Buffer) => {
+        output += chunk.toString()
+      })
+      child.stderr.on('data', (chunk: Buffer) => {
+        output += chunk.toString()
+      })
+      const timer = setTimeout(() => child.kill(), 4000)
+      const closed = new Promise<number | null>((resolve, reject) => {
+        child.once('close', resolve)
+        child.once('error', reject)
+      })
+      if (payloadCase !== 'no-endpoint') {
+        child.stdin.write(
+          JSON.stringify({
+            text:
+              payloadCase === 'oversized'
+                ? 'x'.repeat(1_000_001)
+                : payloadCase === 'encoded-oversized'
+                  ? '日'.repeat(150_000)
+                  : 'hung-request'
+          })
+        )
+      }
+      expect(await closed, payloadCase).toBe(0)
+      clearTimeout(timer)
+      child.stdin.destroy()
+      expect(output, payloadCase).toBe('')
+      expect(requests - before, payloadCase).toBe(payloadCase === 'hung-http' ? 1 : 0)
+    }
+  } finally {
+    server.closeAllConnections()
+    await new Promise<void>((resolve) => server.close(() => resolve()))
+  }
+}, 15_000)
diff --git a/src/main/antigravity/windows-hook-json-post.ts b/src/main/antigravity/windows-hook-json-post.ts
new file mode 100644
index 00000000000..736ae3a4fd1
--- /dev/null
+++ b/src/main/antigravity/windows-hook-json-post.ts
@@ -0,0 +1,92 @@
+import { HOOK_REQUEST_MAX_BYTES } from '../../shared/agent-hook-listener/request-body'
+import {
+  POSIX_HOOK_JSON_STDIN_FIRST_BYTE_TIMEOUT_SECONDS,
+  POSIX_HOOK_JSON_STDIN_IDLE_TIMEOUT_SECONDS
+} from '../agent-hooks/hook-stdin-contract'
+
+// curl reads payload@- before starting its timeout; agy can keep that pipe open.
+export const WINDOWS_ANTIGRAVITY_JSON_POST_SCRIPT = String.raw`
+const http = require('node:http');
+const { StringDecoder } = require('node:string_decoder');
+const env = process.env;
+const port = Number(env.ORCA_AGENT_HOOK_PORT);
+if (!Number.isInteger(port) || port < 1 || port > 65535 || !env.ORCA_AGENT_HOOK_TOKEN || !env.ORCA_PANE_KEY) process.exit(0);
+const decoder = new StringDecoder('utf8');
+let payload = '';
+let finished = false;
+let byteLength = 0;
+let started = false;
+let inString = false;
+let escaped = false;
+let complete = false;
+let invalid = false;
+const stack = [];
+const maxBytes = ${HOOK_REQUEST_MAX_BYTES};
+let idleTimer;
+const absoluteTimer = setTimeout(finish, 7000);
+function finish() {
+  if (finished) return;
+  finished = true;
+  clearTimeout(idleTimer);
+  clearTimeout(absoluteTimer);
+  process.stdin.pause();
+  payload += decoder.end();
+  const form = new URLSearchParams();
+  for (const [name, variable] of [
+    ['paneKey', 'ORCA_PANE_KEY'], ['tabId', 'ORCA_TAB_ID'],
+    ['launchToken', 'ORCA_AGENT_LAUNCH_TOKEN'], ['worktreeId', 'ORCA_WORKTREE_ID'],
+    ['env', 'ORCA_AGENT_HOOK_ENV'], ['version', 'ORCA_AGENT_HOOK_VERSION'],
+    ['hook_event_name', 'ORCA_ANTIGRAVITY_EVENT']
+  ]) form.set(name, env[variable] || '');
+  form.set('payload', payload.trim() ? payload : '{}');
+  const body = form.toString();
+  if (Buffer.byteLength(body) > maxBytes) process.exit(0);
+  let request;
+  const exit = () => { if (request) request.destroy(); process.exit(0); };
+  const postTimer = setTimeout(exit, 1500);
+  try {
+    request = http.request({ hostname: '127.0.0.1', port, path: '/hook/antigravity', method: 'POST', headers: {
+      'Content-Type': 'application/x-www-form-urlencoded',
+      'Content-Length': Buffer.byteLength(body),
+      'X-Orca-Agent-Hook-Token': env.ORCA_AGENT_HOOK_TOKEN
+    } }, response => { response.resume(); response.on('end', () => { clearTimeout(postTimer); exit(); }); });
+    request.on('error', () => { clearTimeout(postTimer); exit(); });
+    request.end(body);
+  } catch { clearTimeout(postTimer); exit(); }
+}
+function resetIdle(timeout) { clearTimeout(idleTimer); idleTimer = setTimeout(finish, timeout); }
+resetIdle(${POSIX_HOOK_JSON_STDIN_FIRST_BYTE_TIMEOUT_SECONDS * 1000});
+process.stdin.on('data', chunk => {
+  if (finished) return;
+  byteLength += chunk.length;
+  if (byteLength > maxBytes) process.exit(0);
+  const text = decoder.write(chunk);
+  payload += text;
+  resetIdle(${POSIX_HOOK_JSON_STDIN_IDLE_TIMEOUT_SECONDS * 1000});
+  for (const character of text) {
+    if (invalid) break;
+    if (complete) { if (!/\s/.test(character)) invalid = true; continue; }
+    if (inString) {
+      if (escaped) escaped = false;
+      else if (character === '\\') escaped = true;
+      else if (character === '"') inString = false;
+      continue;
+    }
+    if (!started && /\s/.test(character)) continue;
+    if (!started && character !== '{' && character !== '[') { invalid = true; break; }
+    started = true;
+    if (character === '"') inString = true;
+    else if (character === '{') stack.push('}');
+    else if (character === '[') stack.push(']');
+    else if (character === '}' || character === ']') {
+      if (character !== stack.pop()) { invalid = true; break; }
+      if (!stack.length) complete = true;
+    }
+  }
+  if (complete && !invalid) {
+    try { JSON.parse(payload); finish(); } catch { invalid = true; }
+  }
+});
+process.stdin.on('end', finish);
+process.stdin.on('error', finish);
+`
diff --git a/src/main/antigravity/windows-hook-payload-delivery.test.ts b/src/main/antigravity/windows-hook-payload-delivery.test.ts
index 6c9ca08bd27..b3d4ee698da 100644
--- a/src/main/antigravity/windows-hook-payload-delivery.test.ts
+++ b/src/main/antigravity/windows-hook-payload-delivery.test.ts
@@ -29,7 +29,6 @@ vi.mock('os', async (importOriginal) => {
 import { AntigravityHookService } from './hook-service'
 import { ANTIGRAVITY_EVENTS, ANTIGRAVITY_PRE_TOOL_USE_DECISION } from './hook-events'
 import { getManagedScript, getWindowsWrapperScript } from './hook-script'
-import { WINDOWS_HOOK_STDIN_DRAIN_COMMAND } from '../agent-hooks/hook-stdin-contract'
 
 // Why (#9358/#9941): `!` is legal in a Windows path and in a pane key. Under inherited
 // delayed expansion cmd eats it out of a percent-expanded curl argument, so bake one into
@@ -105,7 +104,8 @@ function runWrapper(
   // Why: `null` abandons stdin instead of closing it — the shape a caller outside an Orca
   // pane produces, and the only way to prove the env guard exits before reading (#11549).
   stdinPayload: string | null = PAYLOAD,
-  delayedExpansion: DelayedExpansion = 'off'
+  delayedExpansion: DelayedExpansion = 'off',
+  keepStdinOpen = false
 ): Promise<HookRun> {
   return new Promise((resolve, reject) => {
     const child = spawn('cmd.exe', [`/v:${delayedExpansion}`, '/d', '/c', wrapperPath], {
@@ -140,7 +140,11 @@ function runWrapper(
     // resolves on the child's own terms.
     child.stdin.on('error', () => {})
     if (stdinPayload !== null) {
-      child.stdin.end(Buffer.from(stdinPayload, 'utf8'))
+      if (keepStdinOpen) {
+        child.stdin.write(Buffer.from(stdinPayload, 'utf8'))
+      } else {
+        child.stdin.end(Buffer.from(stdinPayload, 'utf8'))
+      }
     }
   })
 }
@@ -164,14 +168,8 @@ function expectedStdout(eventName: string): string {
 describe('Antigravity Windows hook post command', () => {
   it.each(ANTIGRAVITY_EVENTS)('guards missing-core stdin for $eventName', ({ eventName }) => {
     const script = getWindowsWrapperScript(eventName)
-    const drain = script.indexOf(WINDOWS_HOOK_STDIN_DRAIN_COMMAND)
-    const answer = script.lastIndexOf('echo {}')
-    expect(drain).toBeGreaterThan(answer)
-    for (const key of ['ORCA_AGENT_HOOK_PORT', 'ORCA_AGENT_HOOK_TOKEN', 'ORCA_PANE_KEY']) {
-      const guard = script.indexOf(`if "%${key}%"=="" exit /b 0`)
-      expect(guard, key).toBeGreaterThan(answer)
-      expect(guard, key).toBeLessThan(drain)
-    }
+    expect(script).not.toContain('findstr')
+    expect(script).toContain('exit /b 0')
   })
 
   // Why (#9358/#9941): `%~dp0` carries the hooks path, so an inherited delayed expansion eats
@@ -180,17 +178,13 @@ describe('Antigravity Windows hook post command', () => {
     expect(getWindowsWrapperScript(eventName)).toContain('setlocal DisableDelayedExpansion')
   })
 
-  it('posts through curl.exe rather than a PowerShell interpreter', () => {
+  it('posts with the owned runtime and keeps payloads off the command line', () => {
     vi.spyOn(process, 'platform', 'get').mockReturnValue('win32')
-    const script = getManagedScript('local')
-
-    expect(script).not.toMatch(/powershell/i)
-    expect(script).toContain('"%SystemRoot%\\System32\\curl.exe" -sS -X POST')
-    expect(script).toContain('http://127.0.0.1:%ORCA_AGENT_HOOK_PORT%/hook/antigravity')
-    expect(script).toContain('--data-urlencode "hook_event_name=%ORCA_ANTIGRAVITY_EVENT%"')
-    // Why: keep the payload off the command line so multi-KB tool output cannot trip an
-    // EDR oversized-command-line rule.
-    expect(script).toContain('--data-urlencode "payload@-"')
+    const script = getManagedScript('local', 'C:\\Orca!100%\\Orca.exe')
+    expect(script).not.toMatch(/powershell|curl|payload@-/i)
+    expect(script).toContain('ORCA_AGENT_HOOK_NODE=C:\\Orca!100%%\\Orca.exe')
+    expect(script).toContain('"%ORCA_AGENT_HOOK_NODE%" "%~dp0antigravity-hook-post.cjs"')
+    expect(script).toContain('ELECTRON_RUN_AS_NODE=1')
     expect(script).toContain('setlocal DisableDelayedExpansion')
     vi.restoreAllMocks()
   })
@@ -270,6 +264,34 @@ describe.skipIf(process.platform !== 'win32')('Antigravity Windows hook payload
     // Why: ten wrapper launches plus a real install can overrun the default under load.
   }, 90_000)
 
+  it.each([PAYLOAD, ''])(
+    'returns and posts when stdin remains open (%#)',
+    async (input) => {
+      home = mkdtempSync(join(tmpdir(), 'orca-antigravity-open-'))
+      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({
+          ORCA_AGENT_HOOK_PORT: String(listener.port),
+          ORCA_AGENT_HOOK_TOKEN: HOOK_TOKEN,
+          ORCA_PANE_KEY: PANE_KEY
+        }),
+        input,
+        'on',
+        true
+      )
+      expect(result.timedOut).toBe(false)
+      expect(result.exitCode).toBe(0)
+      expect(result.stdout.trim()).toBe('{}')
+      expect(listener.posts).toHaveLength(1)
+      expect(listener.posts[0].payload).toBe(input || '{}')
+    },
+    15_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.
@@ -295,9 +317,7 @@ describe.skipIf(process.platform !== 'win32')('Antigravity Windows hook payload
     expect(result.timedOut).toBe(false)
     expect(result.exitCode).toBe(0)
     expect(listener.posts).toHaveLength(1)
-    // Why: curl drops a `--data-urlencode name@-` field entirely when stdin is empty, so the
-    // event reaches the listener with no `payload` key — not an empty one.
-    expect(listener.posts[0].payload).toBeNull()
+    expect(listener.posts[0].payload).toBe('{}')
     expect(listener.posts[0].hookEventName).toBe('PreInvocation')
   }, 30_000)
 
@@ -338,9 +358,7 @@ describe.skipIf(process.platform !== 'win32')('Antigravity Windows hook payload
     90_000
   )
 
-  // Why: the guard must not cost the valid path its drain — with the Orca env present the
-  // fallback still owns stdin, so the agent's payload write completes instead of breaking.
-  it('still drains a closed payload for every missing-core event inside a pane', async () => {
+  it('answers every missing-core event inside a pane without waiting for EOF', async () => {
     const hooksDir = await installWithoutCore()
     const listener = await startHookListener()
     server = listener.server
@@ -352,7 +370,13 @@ describe.skipIf(process.platform !== 'win32')('Antigravity Windows hook payload
       ORCA_PANE_KEY: PANE_KEY
     })
     for (const event of ANTIGRAVITY_EVENTS) {
-      const result = await runWrapper(join(hooksDir, event.windowsWrapperFileName), env)
+      const result = await runWrapper(
+        join(hooksDir, event.windowsWrapperFileName),
+        env,
+        PAYLOAD,
+        'on',
+        true
+      )
       expect(result.timedOut, event.eventName).toBe(false)
       expect(result.exitCode, event.eventName).toBe(0)
       expect(result.stdout.trim(), event.eventName).toBe(expectedStdout(event.eventName))
diff --git a/src/main/daemon/pty-subprocess-env-inheritance.test.ts b/src/main/daemon/pty-subprocess-env-inheritance.test.ts
index 636b53d70a1..362b9423c1b 100644
--- a/src/main/daemon/pty-subprocess-env-inheritance.test.ts
+++ b/src/main/daemon/pty-subprocess-env-inheritance.test.ts
@@ -104,6 +104,7 @@ describe('createPtySubprocess', () => {
         cwd: 'C:\\repo',
         env: {
           ORCA_AGENT_TEAMS_TEAM_ID: 'team-test',
+          orca_agent_hook_node: 'C:\\Stale\\node.exe',
           ORCA_PATH_ROOT: 'C:\\Users\\orca\\AppData\\Local',
           PATH: '%orca_path_root%\\agy\\bin;C:\\Windows'
         }
@@ -114,6 +115,8 @@ describe('createPtySubprocess', () => {
       }
     }
 
+    expect(spawnMock.mock.calls.at(-1)?.[2].env.ORCA_AGENT_HOOK_NODE).toBe(process.execPath)
+    expect(spawnMock.mock.calls.at(-1)?.[2].env.orca_agent_hook_node).toBeUndefined()
     expect(spawnMock.mock.calls.at(-1)?.[2].env.PATH).toBe(
       'C:\\Users\\orca\\AppData\\Local\\agy\\bin;C:\\Windows'
     )
diff --git a/src/main/daemon/pty-subprocess/spawn-environment.ts b/src/main/daemon/pty-subprocess/spawn-environment.ts
index a063ffb3dd6..aad4b7ec5e4 100644
--- a/src/main/daemon/pty-subprocess/spawn-environment.ts
+++ b/src/main/daemon/pty-subprocess/spawn-environment.ts
@@ -228,4 +228,13 @@ export function finalizeDaemonPtyEnvironment(
   stripLegacyTerminalShimEnv(env, process.platform)
   dropIncoherentCondaActivationEnv(env, process.platform)
   stripPiProcessOwnerEnv(env)
+  // A live daemon pins this runtime across app updates; callers cannot name the host executable.
+  for (const key of Object.keys(env)) {
+    if (key.toUpperCase() === 'ORCA_AGENT_HOOK_NODE') {
+      delete env[key]
+    }
+  }
+  if (process.platform === 'win32') {
+    env.ORCA_AGENT_HOOK_NODE = process.execPath
+  }
 }
diff --git a/src/main/startup/main-process-preflight.ts b/src/main/startup/main-process-preflight.ts
index 67be830901f..2c1ab5b0743 100644
--- a/src/main/startup/main-process-preflight.ts
+++ b/src/main/startup/main-process-preflight.ts
@@ -1,3 +1,5 @@
+import { antigravityHookService } from '../antigravity/hook-service'
+import { getRelocatedDaemonHost } from '../daemon/daemon-host-relocation'
 import { app, ipcMain, powerMonitor, session } from 'electron'
 import { is } from '@electron-toolkit/utils'
 import os from 'node:os'
@@ -209,6 +211,10 @@ function initializeMainProcessPreflight(options: MainProcessPreflightOptions): b
   // Why captured now: after the dev/E2E override above, and before app.setName('Orca') (whenReady)
   // changes how userData resolves on a case-sensitive filesystem. See persistence.ts:20-28.
   initDataPath()
+  antigravityHookService.setWindowsRuntimePathProvider(
+    () => getRelocatedDaemonHost()?.execPath ?? process.execPath
+  )
+
   // Why: Electron resolves the macOS safeStorage Keychain service name from the app name before
   // ready. Dev pins userData above, so applying its name here cannot shift the captured path.
   if (state.devInstanceIdentity && shouldApplyPreReadyAppName(state.devInstanceIdentity)) {