fix(hooks): do not echo raw input from plugin-hook-bootstrap.js

Rebased onto origin/main (49128b576). Fixtures moved from
scripts/hooks/ to /tmp/ecc-pr2380-fixtures/ per reviewer feedback.

(Original commit b0e49036 was based on cc6724ee; main has since
refactored spawnShell to use a shellArgs variable and added
PowerShell .sh fallback paths. This rebase adapts the
const result = spawnSync(...) + __rawInput tagging pattern to
all three spawnSync call sites in spawnShell.)

scripts/hooks/plugin-hook-bootstrap.js

@@ -22,15 +22,40 @@ function writeStderr(stderr) {
   }
 }
 
-function passthrough(raw, result) {
+function passthrough(result) {
   const stdout = typeof result?.stdout === 'string' ? result.stdout : '';
   if (stdout) {
+    // Most ECC hook scripts follow a `run(rawInput) -> rawInput` passthrough
+    // pattern: they do their work, then return the original input so the hook
+    // chain's tool result is preserved. The harness then writes the verbatim
+    // raw input (tool_input + tool_response, often 1-275 KB) into the session
+    // transcript as a hook_success attachment -- ~89% of every ECC session's
+    // transcript is this bloat. Detect the passthrough and emit empty stdout
+    // instead; the harness falls back to the tool_use's original result, the
+    // same path #2240 established for bash-hook-dispatcher.
+    //
+    // IMPORTANT: a strict `stdout === raw` check misses the common case where
+    // child processes' synchronous `process.stdout.write()` writes hit the
+    // ~64 KB Node.js pipe buffer and get truncated -- stdout is then exactly
+    // 65536 bytes and a strict prefix of raw. So we also detect that
+    // truncation sentinel.
+    const raw = typeof result?.__rawInput === 'string' ? result.__rawInput : '';
+    const STDOUT_PIPE_CAP = 64 * 1024;
+    const looksLikePassthrough =
+      (stdout.length === STDOUT_PIPE_CAP && raw.startsWith(stdout)) ||
+      (raw.length > 0 && stdout === raw);
+    if (looksLikePassthrough) {
+      writeStderr(
+        '[Hook] bootstrap: hook returned raw input as stdout; emitting empty to avoid transcript bloat\n'
+      );
+      return;
+    }
     process.stdout.write(stdout);
     return;
   }
 
   if (!Number.isInteger(result?.status) || result.status === 0) {
-    process.stdout.write(raw);
+    writeStderr('[Hook] bootstrap: hook produced no output; emitting empty stdout\n');
   }
 }
 
@@ -146,7 +171,7 @@ function spawnNode(rootDir, relPath, raw, args) {
     CLAUDE_PLUGIN_ROOT: rootDir,
     ECC_PLUGIN_ROOT: rootDir,
   };
-  return spawnSync(process.execPath, [resolveTarget(rootDir, relPath), ...args], {
+  const result = spawnSync(process.execPath, [resolveTarget(rootDir, relPath), ...args], {
     input: raw,
     encoding: 'utf8',
     env: hookEnv,
@@ -154,6 +179,11 @@ function spawnNode(rootDir, relPath, raw, args) {
     timeout: 30000,
     windowsHide: true,
   });
+  // Tag result with the raw input so passthrough() can detect the
+  // "hook returned raw input as stdout" pattern and suppress it
+  // (the dominant source of session-transcript bloat).
+  result.__rawInput = raw;
+  return result;
 }
 
 // spawnShell is not used by any hook in the shipped hooks.json configuration
@@ -190,7 +220,7 @@ function spawnShell(rootDir, relPath, raw, args) {
         stderr: '[Hook] .sh script requested but no bash binary found on Windows; skipping\n',
       };
     }
-    return spawnSync(bash, [scriptPath, ...args], {
+    const bashResult = spawnSync(bash, [scriptPath, ...args], {
       input: raw,
       encoding: 'utf8',
       env: hookEnv,
@@ -198,6 +228,8 @@ function spawnShell(rootDir, relPath, raw, args) {
       timeout: 30000,
       windowsHide: true,
     });
+    bashResult.__rawInput = raw;
+    return bashResult;
   }
 
   const shellArgs = isPs
@@ -206,7 +238,7 @@ function spawnShell(rootDir, relPath, raw, args) {
     ? ['-NoProfile', '-NonInteractive', '-ExecutionPolicy', 'Bypass', '-File', scriptPath, ...args]
     : [scriptPath, ...args];
 
-  return spawnSync(shell, shellArgs, {
+  const result = spawnSync(shell, shellArgs, {
     input: raw,
     encoding: 'utf8',
     env: hookEnv,
@@ -214,6 +246,8 @@ function spawnShell(rootDir, relPath, raw, args) {
     timeout: 30000,
     windowsHide: true,
   });
+  result.__rawInput = raw;
+  return result;
 }
 
 function main() {
@@ -224,7 +258,9 @@ function main() {
   );
 
   if (!mode || !relPath || !rootDir) {
-    process.stdout.write(raw);
+    writeStderr(
+      '[Hook] bootstrap: missing required args (mode/relPath/rootDir); emitting empty stdout\n'
+    );
     process.exit(0);
   }
 
@@ -235,17 +271,15 @@ function main() {
     } else if (mode === 'shell') {
       result = spawnShell(rootDir, relPath, raw, args);
     } else {
-      writeStderr(`[Hook] unknown bootstrap mode: ${mode}\n`);
+      writeStderr(`[Hook] unknown bootstrap mode: ${mode}; emitting empty stdout\n`);
-      process.stdout.write(raw);
       process.exit(0);
     }
   } catch (error) {
-    writeStderr(`[Hook] bootstrap resolution failed: ${error.message}\n`);
+    writeStderr(`[Hook] bootstrap resolution failed: ${error.message}; emitting empty stdout\n`);
-    process.stdout.write(raw);
     process.exit(0);
   }
 
-  passthrough(raw, result);
+  passthrough(result);
   writeStderr(result.stderr);
 
   if (result.error || result.signal || result.status === null) {

tests/hooks/plugin-hook-bootstrap-no-echo.test.js

@@ -0,0 +1,256 @@
+/**
+ * Regression tests for plugin-hook-bootstrap.js raw-echo bloat.
+ *
+ * Before the fix, every fallthrough path in plugin-hook-bootstrap.js
+ * (the actual entry point used by ECC plugin hooks, NOT run-with-flags.js)
+ * echoed the full raw hook input JSON to stdout. For a typical
+ * PostToolUse:Edit payload this is 10-130 KB of tool_input + tool_response
+ * per tool call. The harness then wrote that stdout into the session
+ * transcript as a hook_success attachment, ballooning 51 transcripts
+ * to a combined 1.06 GB (89% of which was raw-echo bloat).
+ *
+ * The fix removes the 4 echo-raw sites in plugin-hook-bootstrap.js:
+ *   - line 137: missing mode/relPath/rootDir
+ *   - line 149: unknown mode
+ *   - line 154: catch on spawn failure
+ *   - line 31: passthrough() default when hook outputs nothing
+ *
+ * For each, we emit empty stdout and a stderr explanation. The harness
+ * then falls back to the tool_use's original result, mirroring the
+ * pattern already shipped in #2240 (bash-hook-dispatcher.js) and #2227
+ * (run-with-flags.js truncation path).
+ *
+ * Related:
+ *   - #2222 / #2227 — fixed the *truncated* path of run-with-flags.js
+ *   - #2239 / #2240 — fixed the same bug in bash-hook-dispatcher.js
+ *   - #1575 — "token limit so fast" (symptom caused in part by this)
+ *
+ * Fixtures live under `/tmp/ecc-pr2380-fixtures/` (per reviewer feedback
+ * on #2380 — keep temp fixture files out of the live scripts/hooks/ tree).
+ */
+
+'use strict';
+
+const assert = require('assert');
+const fs = require('fs');
+const path = require('path');
+const { spawnSync } = require('child_process');
+
+const repoRoot = path.join(__dirname, '..', '..');
+const bootstrap = path.join(repoRoot, 'scripts', 'hooks', 'plugin-hook-bootstrap.js');
+const FIXTURE_DIR = '/tmp/ecc-pr2380-fixtures';
+
+function ensureFixtureDir() {
+  fs.mkdirSync(FIXTURE_DIR, { recursive: true });
+}
+
+function test(name, fn) {
+  try {
+    fn();
+    console.log(`  ✓ ${name}`);
+    return true;
+  } catch (error) {
+    console.log(`  ✗ ${name}`);
+    console.log(`    Error: ${error.message}`);
+    return false;
+  }
+}
+
+function runBootstrap(args, input, env) {
+  return spawnSync('node', [bootstrap, ...args], {
+    input,
+    encoding: 'utf8',
+    cwd: repoRoot,
+    env: { ...process.env, ...(env || {}) },
+    timeout: 30000,
+    maxBuffer: 16 * 1024 * 1024,
+    stdio: ['pipe', 'pipe', 'pipe']
+  });
+}
+
+function realisticPostToolUseEditPayload() {
+  return JSON.stringify({
+    session_id: 'test-session',
+    transcript_path: '/tmp/test.jsonl',
+    cwd: '/tmp',
+    permission_mode: 'auto',
+    hook_event_name: 'PostToolUse',
+    tool_name: 'Edit',
+    tool_input: {
+      file_path: '/tmp/example.ts',
+      old_string: 'a'.repeat(200),
+      new_string: 'b'.repeat(200)
+    },
+    tool_response: { filePath: '/tmp/example.ts', diff: 'c'.repeat(100 * 1024) },
+    tool_use_id: 'call_test_1'
+  });
+}
+
+console.log('\nplugin-hook-bootstrap raw-echo (no bloat) tests:');
+
+ensureFixtureDir();
+
+let passed = 0;
+let failed = 0;
+
+// --- Bug site #1: line 137 (missing args) ---
+if (
+  test('fallthrough 1: missing mode emits empty stdout (no raw echo)', () => {
+    const payload = realisticPostToolUseEditPayload();
+    const result = runBootstrap([], payload, {
+      CLAUDE_PLUGIN_ROOT: repoRoot
+    });
+    assert.strictEqual(result.status, 0);
+    assert.strictEqual(result.stdout, '', 'missing-args path must NOT echo raw input (was ' + result.stdout.length + ' bytes)');
+  })
+)
+  passed++;
+else failed++;
+
+// --- Bug site #2: line 149 (unknown mode) ---
+if (
+  test('fallthrough 2: unknown mode emits empty stdout (no raw echo)', () => {
+    const payload = realisticPostToolUseEditPayload();
+    const result = runBootstrap(['bogus-mode', path.join(FIXTURE_DIR, 'noop-hook-fixture.js')], payload, {
+      CLAUDE_PLUGIN_ROOT: repoRoot
+    });
+    assert.strictEqual(result.status, 0);
+    assert.strictEqual(result.stdout, '', 'unknown-mode path must NOT echo raw input (was ' + result.stdout.length + ' bytes)');
+    assert.match(result.stderr, /unknown bootstrap mode/);
+  })
+)
+  passed++;
+else failed++;
+
+// --- Bug site #3: line 31 (passthrough default) — THE CORE BUG ---
+// This is what fires on EVERY successful hook call where the hook script
+// itself didn't write to stdout. The default `passthrough` behavior is
+// to echo raw input — which is the bulk of the bloat.
+if (
+  test('fallthrough 3: silent hook does NOT echo raw input (the core bug)', () => {
+    const payload = realisticPostToolUseEditPayload();
+    // A no-op node hook that reads stdin and exits silently. Lives in
+    // /tmp/ecc-pr2380-fixtures/ — NOT in the live scripts/hooks/ tree.
+    const noopHookPath = path.join(FIXTURE_DIR, 'noop-hook-fixture.js');
+    fs.writeFileSync(noopHookPath, "process.stdin.resume(); process.stdin.on('end', () => process.exit(0));");
+    try {
+      const result = runBootstrap(['node', noopHookPath], payload, {
+        CLAUDE_PLUGIN_ROOT: repoRoot
+      });
+      assert.strictEqual(result.status, 0);
+      assert.strictEqual(result.stdout, '', 'silent hook must NOT echo raw input (was ' + result.stdout.length + ' bytes)');
+    } finally {
+      fs.unlinkSync(noopHookPath);
+    }
+  })
+)
+  passed++;
+else failed++;
+
+// --- Bug site #4: tool_response leak guard (the user-visible symptom) ---
+if (
+  test('fallthrough 4: tool_response contents never leak into stdout', () => {
+    const marker = 'PAYLOAD_MARKER_DO_NOT_LEAK_X9Z42';
+    const payload = JSON.stringify({
+      session_id: 'test',
+      hook_event_name: 'PostToolUse',
+      tool_name: 'Edit',
+      tool_input: { file_path: '/tmp/x', old_string: 'A', new_string: 'B' },
+      tool_response: { filePath: '/tmp/x', leaked: marker, diff: 'x'.repeat(50 * 1024) }
+    });
+    const result = runBootstrap([], payload, {
+      CLAUDE_PLUGIN_ROOT: repoRoot
+    });
+    assert.strictEqual(result.status, 0);
+    assert.ok(!result.stdout.includes(marker), 'tool_response contents must not appear in stdout');
+  })
+)
+  passed++;
+else failed++;
+
+// --- GREEN-side: behavior we want preserved ---
+if (
+  test('GREEN: hook that outputs JSON is passed through unchanged', () => {
+    // When the hook legitimately produces output (e.g., PreToolUse
+    // additionalContext), we must preserve that output verbatim.
+    const fixturePath = path.join(FIXTURE_DIR, 'echo-fixture.js');
+    const expectedOutput = '{"hookSpecificOutput":{"permissionDecision":"allow"}}\n';
+    fs.writeFileSync(
+      fixturePath,
+      "process.stdin.resume(); process.stdin.on('end', () => { process.stdout.write('" + expectedOutput.replace(/\n/g, '\\n') + "'); process.exit(0); });"
+    );
+    try {
+      const payload = realisticPostToolUseEditPayload();
+      const result = runBootstrap(['node', fixturePath], payload, {
+        CLAUDE_PLUGIN_ROOT: repoRoot
+      });
+      assert.strictEqual(result.status, 0);
+      assert.ok(result.stdout.length > 0, 'hook that produced output should have non-empty stdout');
+      // Must not contain the raw input — only the hook's own output
+      assert.ok(!result.stdout.includes('tool_response'), 'when hook outputs its own stdout, raw input must not also be echoed');
+    } finally {
+      fs.unlinkSync(fixturePath);
+    }
+  })
+)
+  passed++;
+else failed++;
+
+// --- THE CORE ECC PATTERN: most ECC hooks do `process.stdout.write(run(data))`
+//     where run(data) returns the raw input unchanged. Bootstrap must detect
+//     this and emit empty stdout instead of writing raw back. ---
+if (
+  test('CORE ECC PATTERN: hook returning raw input as stdout is suppressed', () => {
+    // Simulate the post-edit-accumulator pattern: read stdin, return it
+    // unchanged via process.stdout.write. This is THE dominant source of
+    // transcript bloat — 12+ ECC hook scripts use this exact pattern.
+    const fixturePath = path.join(FIXTURE_DIR, 'passthrough-fixture.js');
+    fs.writeFileSync(
+      fixturePath,
+      "let d=''; process.stdin.setEncoding('utf8'); process.stdin.on('data', c => d += c); process.stdin.on('end', () => { process.stdout.write(d); process.exit(0); });"
+    );
+    try {
+      const payload = realisticPostToolUseEditPayload();
+      const result = runBootstrap(['node', fixturePath], payload, {
+        CLAUDE_PLUGIN_ROOT: repoRoot
+      });
+      assert.strictEqual(result.status, 0);
+      assert.strictEqual(result.stdout, '', 'hook that returned raw input as stdout must be suppressed (was ' + result.stdout.length + ' bytes)');
+      assert.match(result.stderr, /returned raw input as stdout/, 'stderr should explain the suppression');
+    } finally {
+      fs.unlinkSync(fixturePath);
+    }
+  })
+)
+  passed++;
+else failed++;
+
+// --- Regression guard: hook with its OWN non-raw output (not equal to raw)
+//     must still pass through unchanged. ---
+if (
+  test('hook with its own non-raw output passes through unchanged', () => {
+    const fixturePath = path.join(FIXTURE_DIR, 'own-output-fixture.js');
+    const ownOutput = '{"hookSpecificOutput":{"additionalContext":"hello"}}\n';
+    fs.writeFileSync(
+      fixturePath,
+      "process.stdin.resume(); process.stdin.on('end', () => { process.stdout.write('" + ownOutput.replace(/\n/g, '\\n').replace(/"/g, '\\"') + "'); process.exit(0); });"
+    );
+    try {
+      const payload = realisticPostToolUseEditPayload();
+      const result = runBootstrap(['node', fixturePath], payload, {
+        CLAUDE_PLUGIN_ROOT: repoRoot
+      });
+      assert.strictEqual(result.status, 0);
+      // Should contain the hook's own output, not the raw input
+      assert.ok(result.stdout.includes('additionalContext'), 'hook own output must be preserved');
+      assert.ok(!result.stdout.includes('tool_response'), 'raw input must NOT be echoed when hook has its own output');
+    } finally {
+      fs.unlinkSync(fixturePath);
+    }
+  })
+)
+  passed++;
+else failed++;
+
+console.log('\n  ' + passed + ' passed, ' + failed + ' failed\n');
+process.exit(failed > 0 ? 1 : 0);

tests/hooks/plugin-hook-bootstrap.test.js

@@ -61,12 +61,14 @@ function runTests() {
   let passed = 0;
   let failed = 0;
 
-  if (test('passes stdin through when required bootstrap inputs are missing', () => {
+  if (test('emits empty stdout and stderr warning when required bootstrap inputs are missing', () => {
     const result = run([], { input: '{"ok":true}' });
 
     assert.strictEqual(result.status, 0);
-    assert.strictEqual(result.stdout, '{"ok":true}');
+    // Empty stdout (not the raw input) so the harness falls back to the
-    assert.strictEqual(result.stderr, '');
+    // tool_use's original result -- prevents session-transcript bloat.
+    assert.strictEqual(result.stdout, '');
+    assert.ok(result.stderr.includes('missing required args'));
   })) passed++; else failed++;
 
   if (test('normalizes Windows Git Bash POSIX drive roots', () => {
@@ -143,7 +145,7 @@ process.stdout.write(JSON.stringify({
     }
   })) passed++; else failed++;
 
-  if (test('node mode passes original stdin when child exits cleanly without stdout', () => {
+  if (test('node mode emits empty stdout when child exits cleanly without stdout', () => {
     const root = createTempDir();
     try {
       writeFile(root, path.join('scripts', 'silent.js'), 'process.exit(0);\n');
@@ -154,7 +156,10 @@ process.stdout.write(JSON.stringify({
       });
 
       assert.strictEqual(result.status, 0);
-      assert.strictEqual(result.stdout, 'raw-input');
+      // Empty stdout (not the raw input) -- the dominant source of
+      // session-transcript bloat pre-fix.
+      assert.strictEqual(result.stdout, '');
+      assert.ok(result.stderr.includes('emitting empty stdout'));
     } finally {
       cleanup(root);
     }
@@ -225,7 +230,7 @@ process.exit(7);
     }
   })) passed++; else failed++;
 
-  if (test('shell mode fails open when no shell runtime is available', () => {
+  if (test('shell mode fails open with empty stdout when no shell runtime is available', () => {
     const root = createTempDir();
     try {
       writeFile(root, path.join('scripts', 'hook.sh'), 'printf unreachable\n');
@@ -237,14 +242,16 @@ process.exit(7);
       });
 
       assert.strictEqual(result.status, 0);
-      assert.strictEqual(result.stdout, 'raw-input');
+      // Empty stdout (not the raw input) so the harness falls back to the
+      // tool_use's original result.
+      assert.strictEqual(result.stdout, '');
       assert.ok(result.stderr.includes('shell runtime unavailable'));
     } finally {
       cleanup(root);
     }
   })) passed++; else failed++;
 
-  if (test('rejects target paths that escape the plugin root', () => {
+  if (test('rejects target paths that escape the plugin root with empty stdout', () => {
     const root = createTempDir();
     try {
       const result = run(['node', path.join('..', 'outside.js')], {
@@ -253,14 +260,16 @@ process.exit(7);
       });
 
       assert.strictEqual(result.status, 0);
-      assert.strictEqual(result.stdout, 'raw-input');
+      // Empty stdout (not the raw input) -- the resolver throws, fallthrough
+      // path emits empty + stderr explanation.
+      assert.strictEqual(result.stdout, '');
       assert.ok(result.stderr.includes('Path traversal rejected'));
     } finally {
       cleanup(root);
     }
   })) passed++; else failed++;
 
-  if (test('unknown mode fails open with stderr warning', () => {
+  if (test('unknown mode fails open with empty stdout and stderr warning', () => {
     const root = createTempDir();
     try {
       const result = run(['python', 'hook.py'], {
@@ -269,7 +278,9 @@ process.exit(7);
       });
 
       assert.strictEqual(result.status, 0);
-      assert.strictEqual(result.stdout, 'raw-input');
+      // Empty stdout (not the raw input) -- unknown mode fallthrough path
+      // emits empty + stderr explanation.
+      assert.strictEqual(result.stdout, '');
       assert.ok(result.stderr.includes('unknown bootstrap mode: python'));
     } finally {
       cleanup(root);
@@ -375,7 +386,7 @@ process.exit(7);
         });
 
         assert.strictEqual(result.status, 0);
-        assert.strictEqual(result.stdout, 'raw-input');
+        assert.strictEqual(result.stdout, '');
         assert.ok(
           result.stderr.includes('no bash binary found') ||
           result.stderr.includes('shell runtime unavailable'),