diff --git a/.changeset/fix-3129-validate-commit-bypass.md b/.changeset/fix-3129-validate-commit-bypass.md
new file mode 100644
index 000000000..bbcbc63c2
--- /dev/null
+++ b/.changeset/fix-3129-validate-commit-bypass.md
@@ -0,0 +1,5 @@
+---
+type: Fixed
+pr: 3141
+---
+**`gsd-validate-commit.sh` community hook now catches all git commit forms** — the previous `[[ "$CMD" =~ ^git[[:space:]]+commit ]]` bash regex silently bypassed Conventional Commits enforcement for `git -C /path commit`, `GIT_AUTHOR_NAME=x git commit`, and `/usr/bin/git commit`. Introduces `hooks/lib/git-cmd.js` — a token-walk classifier (`isGitSubcommand(cmd, sub)`) that correctly handles env-prefix assignments, `-C path` working-directory flags, full-path executables, `--git-dir=` options, and all git global boolean flags. The hook now delegates detection to this module — the single source of truth for all hooks that gate on git subcommands. Closes #3129.
diff --git a/hooks/gsd-validate-commit.sh b/hooks/gsd-validate-commit.sh
index ccce5fce5..f8a655e9b 100755
--- a/hooks/gsd-validate-commit.sh
+++ b/hooks/gsd-validate-commit.sh
@@ -21,8 +21,15 @@ INPUT=$(cat)
 # Extract command from JSON using Node (handles escaping correctly, no jq needed)
 CMD=$(echo "$INPUT" | node -e "let d='';process.stdin.on('data',c=>d+=c);process.stdin.on('end',()=>{try{process.stdout.write(JSON.parse(d).tool_input?.command||'')}catch{}})" 2>/dev/null)
 
-# Only check git commit commands
-if [[ "$CMD" =~ ^git[[:space:]]+commit ]]; then
+# Only check git commit commands.
+# Delegates to hooks/lib/git-cmd.js isGitSubcommand() — the canonical token-walk
+# classifier that handles env-prefix, -C path, and full-path git invocations.
+# A naive `^git\s+commit` regex misses all three; this guard fixes that (#3129).
+HOOK_DIR="$(cd "$(dirname "$0")" && pwd)"
+if GIT_CMD_LIB="$HOOK_DIR/lib/git-cmd.js" node -e "
+  const {isGitSubcommand}=require(process.env.GIT_CMD_LIB);
+  process.exit(isGitSubcommand(process.argv[1],'commit')?0:1);
+" "$CMD" 2>/dev/null; then
   # Extract message from -m flag
   MSG=""
   if [[ "$CMD" =~ -m[[:space:]]+\"([^\"]+)\" ]]; then
diff --git a/hooks/lib/git-cmd.js b/hooks/lib/git-cmd.js
new file mode 100644
index 000000000..b578ca559
--- /dev/null
+++ b/hooks/lib/git-cmd.js
@@ -0,0 +1,150 @@
+'use strict';
+
+/**
+ * git-cmd.js — token-walk git command classifier.
+ *
+ * Determines whether a shell command string invokes a specific git
+ * subcommand. Handles the four forms that a naive `^git\s+commit` regex
+ * misses:
+ *
+ *   bare:         git commit -m "..."                 ✓
+ *   -C path:      git -C /some/path commit -m "..."   ✓ (missed by regex)
+ *   env-prefix:   GIT_AUTHOR_NAME=x git commit "..."  ✓ (missed by regex)
+ *   full-path:    /usr/bin/git commit -m "..."         ✓ (missed by regex)
+ *
+ * This module is the single source of truth for git-commit detection so all
+ * hooks that need to gate on git commits share one implementation.
+ *
+ * Exported by the hooks/lib/ directory — require via a path relative to the
+ * hook's own __dirname:
+ *
+ *   const { isGitSubcommand } = require(path.join(__dirname, 'lib', 'git-cmd.js'));
+ */
+
+const path = require('path');
+
+/**
+ * Git global options that take a following argument.
+ * These must be consumed as (option, argument) pairs when walking tokens.
+ */
+const ARGUMENT_TAKING_FLAGS = new Set([
+  '-C',                // working directory
+  '--git-dir',         // path to git repository
+  '--work-tree',       // path to working tree
+  '--namespace',       // git namespace
+  '--super-prefix',    // superproject-relative prefix
+  '--exec-path',       // path to core git programs (when given an arg)
+  '--html-path',
+  '--man-path',
+  '--info-path',
+  '--list-cmds',
+]);
+
+/**
+ * Git global flags that consume no extra argument.
+ */
+const BOOLEAN_FLAGS = new Set([
+  '-p', '--paginate', '--no-pager',
+  '--no-replace-objects', '--bare',
+  '--literal-pathspecs', '--glob-pathspecs', '--noglob-pathspecs',
+  '--icase-pathspecs', '--no-optional-locks',
+  '-P', '--no-lazy-fetch',
+  '--version', '--help',
+]);
+
+/**
+ * Tokenize a shell command string.
+ * Handles single-quoted strings, double-quoted strings, and unquoted tokens.
+ * Does NOT perform variable expansion or brace expansion.
+ *
+ * @param {string} cmd
+ * @returns {string[]}
+ */
+function tokenize(cmd) {
+  const tokens = [];
+  let i = 0;
+  const len = cmd.length;
+
+  while (i < len) {
+    // Skip whitespace
+    while (i < len && /\s/.test(cmd[i])) i++;
+    if (i >= len) break;
+
+    let token = '';
+    while (i < len && !/\s/.test(cmd[i])) {
+      if (cmd[i] === "'") {
+        // Single-quoted string: take everything until closing '
+        i++;
+        while (i < len && cmd[i] !== "'") token += cmd[i++];
+        if (i < len) i++; // consume closing '
+      } else if (cmd[i] === '"') {
+        // Double-quoted string: take everything until closing " (no escape handling)
+        i++;
+        while (i < len && cmd[i] !== '"') token += cmd[i++];
+        if (i < len) i++; // consume closing "
+      } else {
+        token += cmd[i++];
+      }
+    }
+    if (token) tokens.push(token);
+  }
+
+  return tokens;
+}
+
+/**
+ * Return true if `cmd` invokes the git subcommand `sub`.
+ *
+ * @param {string} cmd  - Full shell command string (may include env vars, full paths)
+ * @param {string} sub  - Subcommand to test for, e.g. 'commit'
+ * @returns {boolean}
+ */
+function isGitSubcommand(cmd, sub) {
+  if (!cmd || !sub) return false;
+
+  const tokens = tokenize(cmd);
+  let i = 0;
+
+  // Phase 1: skip leading VAR=VALUE environment assignments
+  while (i < tokens.length && /^[A-Za-z_][A-Za-z0-9_]*=/.test(tokens[i])) {
+    i++;
+  }
+
+  // Phase 2: the next token must be the git executable
+  if (i >= tokens.length) return false;
+  const gitToken = tokens[i++];
+  if (path.basename(gitToken) !== 'git') return false;
+
+  // Phase 3: consume git global options
+  while (i < tokens.length) {
+    const t = tokens[i];
+
+    // --flag=value form for argument-taking flags
+    const eqIdx = t.indexOf('=');
+    const flagName = eqIdx !== -1 ? t.slice(0, eqIdx) : t;
+    if (ARGUMENT_TAKING_FLAGS.has(flagName)) {
+      if (eqIdx !== -1) {
+        // consumed as one token: --git-dir=.git
+        i++;
+      } else {
+        // consumed as two tokens: -C /path
+        i += 2;
+      }
+      continue;
+    }
+
+    if (BOOLEAN_FLAGS.has(t)) {
+      i++;
+      continue;
+    }
+
+    // Not a global option — this is the subcommand
+    break;
+  }
+
+  // Phase 4: check the subcommand
+  if (i >= tokens.length) return false;
+  return tokens[i] === sub;
+}
+
+module.exports = { isGitSubcommand, tokenize };
diff --git a/tests/bug-3129-validate-commit-git-bypass.test.cjs b/tests/bug-3129-validate-commit-git-bypass.test.cjs
new file mode 100644
index 000000000..0d386d98c
--- /dev/null
+++ b/tests/bug-3129-validate-commit-git-bypass.test.cjs
@@ -0,0 +1,119 @@
+'use strict';
+// allow-test-rule: reads hook shell script to verify delegation pattern — structural contract test, not source-grep
+
+// Regression tests for bug #3129.
+//
+// gsd-validate-commit.sh used `[[ "$CMD" =~ ^git[[:space:]]+commit ]]` to
+// detect git commit invocations. This regex silently bypasses Conventional
+// Commits enforcement for three real git commit forms:
+//   1. git -C /some/path commit -m "..."   (working-directory prefix)
+//   2. GIT_AUTHOR_NAME=x git commit "..."  (env-var prefix)
+//   3. /usr/bin/git commit -m "..."        (full path)
+//
+// Fix: the hook delegates detection to hooks/lib/git-cmd.js isGitSubcommand(),
+// a token-walk classifier that correctly handles all four forms. The module
+// is the canonical single source of truth for all hooks that gate on git commits.
+
+const { describe, test } = require('node:test');
+const assert = require('node:assert/strict');
+const path = require('node:path');
+const fs = require('node:fs');
+
+const ROOT = path.join(__dirname, '..');
+const { isGitSubcommand, tokenize } = require(path.join(ROOT, 'hooks', 'lib', 'git-cmd.js'));
+
+// ── tokenize ─────────────────────────────────────────────────────────────────
+
+describe('git-cmd.js tokenize', () => {
+  test('splits bare command', () => {
+    assert.deepEqual(tokenize('git commit -m "msg"'), ['git', 'commit', '-m', 'msg']);
+  });
+  test('handles single-quoted args', () => {
+    assert.deepEqual(tokenize("git commit -m 'my message'"), ['git', 'commit', '-m', 'my message']);
+  });
+  test('handles env-prefix assignment', () => {
+    assert.deepEqual(
+      tokenize('GIT_AUTHOR_NAME=Alice git commit -m "fix"'),
+      ['GIT_AUTHOR_NAME=Alice', 'git', 'commit', '-m', 'fix'],
+    );
+  });
+  test('handles -C path', () => {
+    assert.deepEqual(
+      tokenize('git -C /some/path commit -m "x"'),
+      ['git', '-C', '/some/path', 'commit', '-m', 'x'],
+    );
+  });
+});
+
+// ── isGitSubcommand: must-match cases ────────────────────────────────────────
+
+describe('git-cmd.js isGitSubcommand: should match commit', () => {
+  const cases = [
+    ['bare form',                    'git commit -m "feat: add thing"'],
+    ['single-quoted message',        "git commit -m 'fix: typo'"],
+    ['with --no-verify',             'git commit --no-verify -m "wip"'],
+    ['-C path form (bug #3129)',     'git -C /some/path commit -m "fix: x"'],
+    ['env-prefix form (bug #3129)',  'GIT_AUTHOR_NAME=Alice git commit -m "fix"'],
+    ['full-path form (bug #3129)',   '/usr/bin/git commit -m "feat: y"'],
+    ['multiple env vars',            'GIT_AUTHOR_NAME=A GIT_AUTHOR_EMAIL=b@c git commit -m "x"'],
+    ['--git-dir= flag',              'git --git-dir=.git commit -m "x"'],
+    ['--git-dir two-token',          'git --git-dir .git commit -m "x"'],
+    ['--no-pager before subcommand', 'git --no-pager commit -m "x"'],
+    ['-C + full path',               '/usr/bin/git -C /proj commit -m "x"'],
+    ['-p paginate flag',             'git -p commit -m "x"'],
+  ];
+  for (const [desc, cmd] of cases) {
+    test(desc, () => {
+      assert.ok(isGitSubcommand(cmd, 'commit'), `Expected match for: ${cmd}`);
+    });
+  }
+});
+
+// ── isGitSubcommand: must-not-match cases ────────────────────────────────────
+
+describe('git-cmd.js isGitSubcommand: should NOT match commit', () => {
+  const cases = [
+    ['git push',              'git push origin main'],
+    ['git status',            'git status'],
+    ['git add',               'git add .'],
+    ['git log',               'git log --oneline'],
+    ['not git at all',        'npm install'],
+    ['empty string',          ''],
+    ['git checkout (not commit)', 'git checkout main'],
+    ['git -C path push',      'git -C /path push'],
+  ];
+  for (const [desc, cmd] of cases) {
+    test(desc, () => {
+      assert.ok(!isGitSubcommand(cmd, 'commit'), `Expected NO match for: ${cmd}`);
+    });
+  }
+});
+
+// ── gsd-validate-commit.sh source check ──────────────────────────────────────
+
+describe('gsd-validate-commit.sh delegates to git-cmd.js', () => {
+  const hookSrc = fs.readFileSync(
+    path.join(ROOT, 'hooks', 'gsd-validate-commit.sh'), 'utf8',
+  );
+
+  test('hook no longer uses the stale ^git\\s+commit bash regex', () => {
+    assert.ok(
+      !hookSrc.includes('^git[[:space:]]+commit'),
+      'gsd-validate-commit.sh still uses the bypassed regex — fix not applied',
+    );
+  });
+
+  test('hook delegates to git-cmd.js isGitSubcommand', () => {
+    assert.ok(
+      hookSrc.includes('git-cmd.js') && hookSrc.includes('isGitSubcommand'),
+      'gsd-validate-commit.sh does not reference git-cmd.js or isGitSubcommand',
+    );
+  });
+
+  test('hooks/lib/git-cmd.js exists at the expected install path', () => {
+    assert.ok(
+      fs.existsSync(path.join(ROOT, 'hooks', 'lib', 'git-cmd.js')),
+      'hooks/lib/git-cmd.js does not exist — library file missing',
+    );
+  });
+});