diff --git a/CHANGELOG.md b/CHANGELOG.md
index d2ae567..fc1a83b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,9 @@ and adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
 
+### Fixes
+
+- On Windows, the Claude Code prompt hook written by `codegraph install` failed with "command not found" when hooks run through Git Bash, which needs the `.cmd` extension to find the launcher. The installer now writes the platform-correct command, and re-running `codegraph install` (or `codegraph upgrade`) repairs an existing install in place. (#1466)
 
 ## [1.5.0] - 2026-07-21
 
diff --git a/__tests__/installer-targets.test.ts b/__tests__/installer-targets.test.ts
index 6db793d..e6a363e 100644
--- a/__tests__/installer-targets.test.ts
+++ b/__tests__/installer-targets.test.ts
@@ -1144,6 +1144,11 @@ describe('Installer targets — partial-state idempotency', () => {
   // Opt-in (default-yes in the installer) UserPromptSubmit hook that runs
   // `codegraph prompt-hook`. Must write/remove surgically, be idempotent, and
   // round-trip an opt-out — without disturbing the user's own hooks.
+  // Platform-aware since #1466: Windows writes `codegraph.cmd prompt-hook`
+  // (Git Bash applies no PATHEXT, so the bare form is exit 127 there), and
+  // install self-heals the other platform's spelling in place.
+  const HOOK_CMD = process.platform === 'win32' ? 'codegraph.cmd prompt-hook' : 'codegraph prompt-hook';
+  const OTHER_PLATFORM_HOOK_CMD = process.platform === 'win32' ? 'codegraph prompt-hook' : 'codegraph.cmd prompt-hook';
   const promptCommands = (s: any): string[] =>
     (s.hooks?.UserPromptSubmit ?? []).flatMap((g: any) => (g.hooks ?? []).map((h: any) => h.command));
 
@@ -1151,7 +1156,7 @@ describe('Installer targets — partial-state idempotency', () => {
     const claude = getTarget('claude')!;
     claude.install('global', { autoAllow: true, promptHook: true });
     const s = JSON.parse(fs.readFileSync(path.join(tmpHome, '.claude', 'settings.json'), 'utf-8'));
-    expect(promptCommands(s)).toContain('codegraph prompt-hook');
+    expect(promptCommands(s)).toContain(HOOK_CMD);
     expect(s.permissions?.allow).toContain('mcp__codegraph__*');
   });
 
@@ -1159,7 +1164,7 @@ describe('Installer targets — partial-state idempotency', () => {
     const claude = getTarget('claude')!;
     claude.install('global', { autoAllow: true });
     const s = JSON.parse(fs.readFileSync(path.join(tmpHome, '.claude', 'settings.json'), 'utf-8'));
-    expect(promptCommands(s)).not.toContain('codegraph prompt-hook');
+    expect(promptCommands(s)).not.toContain(HOOK_CMD);
   });
 
   it('claude: install with promptHook:true is idempotent (no duplicate, byte-identical re-run)', () => {
@@ -1170,7 +1175,7 @@ describe('Installer targets — partial-state idempotency', () => {
     claude.install('global', { autoAllow: true, promptHook: true });
     expect(fs.readFileSync(file, 'utf-8')).toBe(first);
     const s = JSON.parse(first);
-    expect(promptCommands(s).filter((c: string) => c === 'codegraph prompt-hook')).toHaveLength(1);
+    expect(promptCommands(s).filter((c: string) => c === HOOK_CMD)).toHaveLength(1);
   });
 
   it('claude: install with promptHook:false strips a hook a prior install wrote (opt-out round-trips)', () => {
@@ -1178,7 +1183,7 @@ describe('Installer targets — partial-state idempotency', () => {
     claude.install('global', { autoAllow: true, promptHook: true });
     claude.install('global', { autoAllow: true, promptHook: false });
     const s = JSON.parse(fs.readFileSync(path.join(tmpHome, '.claude', 'settings.json'), 'utf-8'));
-    expect(promptCommands(s)).not.toContain('codegraph prompt-hook');
+    expect(promptCommands(s)).not.toContain(HOOK_CMD);
   });
 
   it('claude: writePromptHookEntry preserves a sibling UserPromptSubmit hook', () => {
@@ -1187,14 +1192,37 @@ describe('Installer targets — partial-state idempotency', () => {
     });
     expect(writePromptHookEntry('global').action).toBe('updated');
     const s = JSON.parse(fs.readFileSync(file, 'utf-8'));
-    expect(promptCommands(s)).toEqual(['my-own-hook', 'codegraph prompt-hook']);
+    expect(promptCommands(s)).toEqual(['my-own-hook', HOOK_CMD]);
+  });
+
+  it('claude: writePromptHookEntry migrates the other platform\'s spelling in place (#1466 self-heal)', () => {
+    const file = seedSettings('global', {
+      hooks: { UserPromptSubmit: [{ hooks: [{ type: 'command', command: OTHER_PLATFORM_HOOK_CMD }] }] },
+    });
+    expect(writePromptHookEntry('global').action).toBe('updated');
+    const s = JSON.parse(fs.readFileSync(file, 'utf-8'));
+    expect(promptCommands(s)).toEqual([HOOK_CMD]);
+    // A re-run after migration is byte-identical.
+    const healed = fs.readFileSync(file, 'utf-8');
+    expect(writePromptHookEntry('global').action).toBe('unchanged');
+    expect(fs.readFileSync(file, 'utf-8')).toBe(healed);
+  });
+
+  it('claude: writePromptHookEntry leaves an npx-form hook untouched (no duplicate, no rewrite)', () => {
+    const npxCmd = 'npx @colbymchenry/codegraph prompt-hook';
+    const file = seedSettings('global', {
+      hooks: { UserPromptSubmit: [{ hooks: [{ type: 'command', command: npxCmd }] }] },
+    });
+    expect(writePromptHookEntry('global').action).toBe('unchanged');
+    const s = JSON.parse(fs.readFileSync(file, 'utf-8'));
+    expect(promptCommands(s)).toEqual([npxCmd]);
   });
 
   it('claude: uninstall removes the prompt hook but keeps the user\'s sibling', () => {
     const file = seedSettings('global', {
       hooks: {
         UserPromptSubmit: [
-          { hooks: [{ type: 'command', command: 'codegraph prompt-hook' }] },
+          { hooks: [{ type: 'command', command: HOOK_CMD }] },
           { hooks: [{ type: 'command', command: 'my-own-hook' }] },
         ],
       },
@@ -1204,16 +1232,27 @@ describe('Installer targets — partial-state idempotency', () => {
     expect(promptCommands(s)).toEqual(['my-own-hook']);
   });
 
+  it('claude: removePromptHookEntry removes the other platform\'s spelling too', () => {
+    const file = seedSettings('global', {
+      hooks: {
+        UserPromptSubmit: [{ hooks: [{ type: 'command', command: OTHER_PLATFORM_HOOK_CMD }] }],
+      },
+    });
+    expect(removePromptHookEntry('global').action).toBe('removed');
+    const s = JSON.parse(fs.readFileSync(file, 'utf-8'));
+    expect(promptCommands(s)).toEqual([]);
+  });
+
   it('claude: removePromptHookEntry leaves the legacy auto-sync hook untouched', () => {
     const file = seedSettings('global', {
       hooks: {
-        UserPromptSubmit: [{ hooks: [{ type: 'command', command: 'codegraph prompt-hook' }] }],
+        UserPromptSubmit: [{ hooks: [{ type: 'command', command: HOOK_CMD }] }],
         Stop: [{ hooks: [{ type: 'command', command: 'codegraph sync-if-dirty' }] }],
       },
     });
     expect(removePromptHookEntry('global').action).toBe('removed');
     const s = JSON.parse(fs.readFileSync(file, 'utf-8'));
-    expect(promptCommands(s)).not.toContain('codegraph prompt-hook');
+    expect(promptCommands(s)).not.toContain(HOOK_CMD);
     const stopCmds = (s.hooks?.Stop ?? []).flatMap((g: any) => (g.hooks ?? []).map((h: any) => h.command));
     expect(stopCmds).toContain('codegraph sync-if-dirty');
   });
diff --git a/src/installer/targets/claude.ts b/src/installer/targets/claude.ts
index bdfe6e6..e95b0a3 100644
--- a/src/installer/targets/claude.ts
+++ b/src/installer/targets/claude.ts
@@ -296,12 +296,24 @@ function isLegacyCodegraphHookCommand(command: unknown): boolean {
 
 /**
  * The front-load prompt-hook command the installer writes into Claude's
- * `UserPromptSubmit` (see writePromptHookEntry). Matched by substring so an
+ * `UserPromptSubmit` (see writePromptHookEntry). On Windows the launcher on
+ * PATH is `codegraph.cmd`, and Claude Code executes hooks through Git Bash,
+ * which — unlike cmd.exe — applies no PATHEXT: a bare `codegraph` is
+ * "command not found", exit 127 (#1466). Write the extension there; the
+ * `.cmd` spelling also resolves fine under cmd.exe and PowerShell.
+ */
+const PROMPT_HOOK_COMMAND = process.platform === 'win32'
+  ? 'codegraph.cmd prompt-hook'
+  : 'codegraph prompt-hook';
+
+/**
+ * Every spelling the installer has ever written (a settings.json can carry
+ * the other platform's form across a sync). Matched by substring so an
  * `npx @colbymchenry/codegraph prompt-hook` form is recognized too.
  */
-const PROMPT_HOOK_COMMAND = 'codegraph prompt-hook';
+const PROMPT_HOOK_FORMS = ['codegraph prompt-hook', 'codegraph.cmd prompt-hook'];
 function isPromptHookCommand(command: unknown): boolean {
-  return typeof command === 'string' && command.includes(PROMPT_HOOK_COMMAND);
+  return typeof command === 'string' && PROMPT_HOOK_FORMS.some((f) => command.includes(f));
 }
 
 /**
@@ -424,10 +436,31 @@ export function writePromptHookEntry(loc: Location): WriteResult['files'][number
   }
   if (!Array.isArray(settings.hooks.UserPromptSubmit)) settings.hooks.UserPromptSubmit = [];
 
+  // Self-heal (#1466): a pre-fix install on Windows wrote the bare
+  // `codegraph prompt-hook`, which Git Bash resolves to nothing; a
+  // settings.json carried across platforms can hold the other spelling too.
+  // Rewrite an installer-written command to this platform's form in place.
+  // Only the exact installer spellings migrate — an `npx …` or hand-edited
+  // variant is the user's own and stays untouched.
+  let migrated = false;
+  for (const group of settings.hooks.UserPromptSubmit) {
+    if (!group || !Array.isArray(group.hooks)) continue;
+    for (const h of group.hooks) {
+      if (h && PROMPT_HOOK_FORMS.includes(h.command) && h.command !== PROMPT_HOOK_COMMAND) {
+        h.command = PROMPT_HOOK_COMMAND;
+        migrated = true;
+      }
+    }
+  }
+
   const already = settings.hooks.UserPromptSubmit.some(
     (g: any) => g && Array.isArray(g.hooks) && g.hooks.some((h: any) => isPromptHookCommand(h?.command)),
   );
-  if (already) return { path: file, action: 'unchanged' };
+  if (already) {
+    if (!migrated) return { path: file, action: 'unchanged' };
+    writeJsonFile(file, settings);
+    return { path: file, action: 'updated' };
+  }
 
   settings.hooks.UserPromptSubmit.push({
     hooks: [{ type: 'command', command: PROMPT_HOOK_COMMAND }],