chore(continuous-learning-v2): standardize shell shebangs to env bash (#2401)

* chore(continuous-learning-v2): standardize shell shebangs to env bash

Three scripts under skills/continuous-learning-v2/ used the hardcoded
`#!/bin/bash` shebang while the other four already used the portable
`#!/usr/bin/env bash`:

- hooks/observe.sh (runs on every hook invocation)
- scripts/detect-project.sh
- agents/start-observer.sh

The hardcoded interpreter path fails to execute on systems where bash is
not installed at /bin/bash (NixOS, some Homebrew layouts, FreeBSD).
Standardize all three to `#!/usr/bin/env bash`, matching the repo-wide
majority convention, and add a regression test that asserts shebang
uniformity for every shell script in this skill so the inconsistency
cannot reappear.

Fixes #2303

* test(continuous-learning-v2): harden shebang test runner

Address review feedback on the shebang-consistency regression test:

- firstLine() now splits on /\r?\n/ so a script checked out with CRLF
  line endings does not leave a trailing carriage return that would
  break the shebang comparison on Windows.
- The test() helper now surfaces the full error (stack trace, not just
  the message) on failure and writes pass/fail lines via
  process.stdout/stderr so diagnostics are preserved.

* test(continuous-learning-v2): skip hidden dirs in shebang scan

The recursive shell-script scan now skips hidden directories (e.g. the
observer's runtime `.observer-tmp`). This keeps the shebang-consistency
check deterministic: only committed skill scripts are examined, and an
untracked local artifact left over from an observer run can no longer
cause a false failure.

skills/continuous-learning-v2/agents/start-observer.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 # Continuous Learning v2 - Observer Agent Launcher
 #
 # Starts the background observer agent that analyzes observations

skills/continuous-learning-v2/hooks/observe.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 # Continuous Learning v2 - Observation Hook
 #
 # Captures tool use events for pattern analysis.

skills/continuous-learning-v2/scripts/detect-project.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 # Continuous Learning v2 - Project Detection Helper
 #
 # Shared logic for detecting current project context.

tests/hooks/continuous-learning-shebang-consistency.test.js

@@ -0,0 +1,101 @@
+/**
+ * Tests for shebang consistency across continuous-learning-v2 shell scripts
+ *
+ * Every `*.sh` script under skills/continuous-learning-v2/ must use the
+ * portable `#!/usr/bin/env bash` shebang rather than the hardcoded
+ * `#!/bin/bash`. The hardcoded interpreter path fails on systems where bash
+ * is not installed at /bin/bash (NixOS, some Homebrew layouts, FreeBSD), and
+ * observe.sh runs on every hook invocation. This guards against the
+ * inconsistency (#2303) reappearing.
+ *
+ * Run with: node tests/hooks/continuous-learning-shebang-consistency.test.js
+ */
+
+'use strict';
+
+const assert = require('assert');
+const path = require('path');
+const fs = require('fs');
+
+let passed = 0;
+let failed = 0;
+
+function test(name, fn) {
+  try {
+    fn();
+    process.stdout.write(`  ✓ ${name}\n`);
+    passed++;
+  } catch (err) {
+    process.stderr.write(`  ✗ ${name}\n`);
+    process.stderr.write(`    ${err && err.stack ? err.stack : String(err)}\n`);
+    failed++;
+  }
+}
+
+const repoRoot = path.resolve(__dirname, '..', '..');
+const skillDir = path.join(repoRoot, 'skills', 'continuous-learning-v2');
+const PORTABLE_SHEBANG = '#!/usr/bin/env bash';
+const HARDCODED_SHEBANG = '#!/bin/bash';
+
+function collectShellScripts(dir, acc = []) {
+  for (const entry of fs.readdirSync(dir, { withFileTypes: true })) {
+    const fullPath = path.join(dir, entry.name);
+    if (entry.isDirectory()) {
+      // Skip hidden/runtime directories (e.g. the observer's `.observer-tmp`)
+      // so an untracked local artifact cannot trigger a false failure; only
+      // committed skill scripts are checked.
+      if (entry.name.startsWith('.')) {
+        continue;
+      }
+      collectShellScripts(fullPath, acc);
+    } else if (entry.isFile() && entry.name.endsWith('.sh')) {
+      acc.push(fullPath);
+    }
+  }
+  return acc;
+}
+
+function firstLine(filePath) {
+  return fs.readFileSync(filePath, 'utf8').split(/\r?\n/, 1)[0];
+}
+
+console.log('\n=== continuous-learning-v2 shebang consistency ===\n');
+
+const scripts = collectShellScripts(skillDir);
+
+test('skill directory contains shell scripts to check', () => {
+  assert.ok(scripts.length > 0, `expected at least one .sh under ${skillDir}`);
+});
+
+for (const scriptPath of scripts) {
+  const rel = path.relative(repoRoot, scriptPath).split(path.sep).join('/');
+  test(`${rel} uses portable '#!/usr/bin/env bash'`, () => {
+    assert.strictEqual(
+      firstLine(scriptPath),
+      PORTABLE_SHEBANG,
+      `${rel} should start with '${PORTABLE_SHEBANG}'`
+    );
+  });
+}
+
+test('no continuous-learning-v2 script uses hardcoded #!/bin/bash', () => {
+  const offenders = scripts
+    .filter(scriptPath => firstLine(scriptPath) === HARDCODED_SHEBANG)
+    .map(scriptPath => path.relative(repoRoot, scriptPath).split(path.sep).join('/'));
+  assert.strictEqual(
+    offenders.length,
+    0,
+    `hardcoded #!/bin/bash found in: ${offenders.join(', ')}`
+  );
+});
+
+// ──────────────────────────────────────────────────────
+// Summary
+// ──────────────────────────────────────────────────────
+
+console.log('\n=== Test Results ===');
+console.log(`Passed: ${passed}`);
+console.log(`Failed: ${failed}`);
+console.log(`Total:  ${passed + failed}\n`);
+
+process.exit(failed > 0 ? 1 : 0);