fix: remove dead delete+recreate and pin code, add poll fallback test

Phase 1 cleanup:
- Remove deletePost() method (dead code, replaced by PUT in-place updates)
- Remove _postInfo Map tracking (no longer needed)
- Remove pin/unpin API calls from watcher-manager.js (incompatible with PUT updates)
- Add JSDoc note on (edited) label limitation in _flushUpdate()
- Add integration test: test/integration/poll-fallback.test.js
- Fix addSession() lastOffset===0 falsy bug (0 was treated as 'no offset')
- Fix pre-existing test failures: add lastOffset:0 where tests expect backlog reads
- Fix pre-existing session-monitor test: create stub transcript files
- Fix pre-existing status-formatter test: update indent check for blockquote format
- Format plugin/ files with Prettier (pre-existing formatting drift)

test/integration/poll-fallback.test.js

@@ -0,0 +1,77 @@
+'use strict';
+
+/**
+ * Integration test: poll-fallback
+ *
+ * Verifies that StatusWatcher detects file changes via the polling fallback
+ * (not just fs.watch). Creates a temp JSONL file, initializes a StatusWatcher,
+ * appends a line, and asserts the 'session-update' event fires within 1000ms.
+ */
+
+var describe = require('node:test').describe;
+var it = require('node:test').it;
+var beforeEach = require('node:test').beforeEach;
+var afterEach = require('node:test').afterEach;
+var assert = require('node:assert/strict');
+var fs = require('fs');
+var path = require('path');
+var os = require('os');
+
+var StatusWatcher = require('../../src/status-watcher').StatusWatcher;
+
+function createTmpDir() {
+  return fs.mkdtempSync(path.join(os.tmpdir(), 'poll-fallback-test-'));
+}
+
+describe('StatusWatcher poll fallback', function () {
+  var tmpDir;
+  var watcher;
+
+  beforeEach(function () {
+    tmpDir = createTmpDir();
+  });
+
+  afterEach(function () {
+    if (watcher) {
+      watcher.stop();
+      watcher = null;
+    }
+    try {
+      fs.rmSync(tmpDir, { recursive: true, force: true });
+    } catch (_e) {
+      /* ignore */
+    }
+  });
+
+  it('emits session-update within 1000ms when a line is appended to the JSONL file', function (t, done) {
+    var transcriptFile = path.join(tmpDir, 'test-session.jsonl');
+    fs.writeFileSync(transcriptFile, '');
+
+    watcher = new StatusWatcher({ transcriptDir: tmpDir, idleTimeoutS: 600 });
+
+    // Use a saved offset of 0 so we read from beginning
+    watcher.addSession('test:poll', transcriptFile, { lastOffset: 0 });
+
+    var timer = setTimeout(function () {
+      done(new Error('session-update event not received within 1000ms'));
+    }, 1000);
+
+    watcher.once('session-update', function (sessionKey) {
+      clearTimeout(timer);
+      assert.equal(sessionKey, 'test:poll');
+      done();
+    });
+
+    // Append a valid JSONL line after a short delay to allow watcher setup
+    setTimeout(function () {
+      var record = {
+        type: 'message',
+        message: {
+          role: 'assistant',
+          content: [{ type: 'text', text: 'Poll fallback test line' }],
+        },
+      };
+      fs.appendFileSync(transcriptFile, JSON.stringify(record) + '\n');
+    }, 100);
+  });
+});