feat: Read My Mind phase 2, the predictor and the brain button

The feature as pitched in docs/readmymind-plan.md: pressing the header
brain button predicts the prompt you were about to type, from the case's
intent profile plus everything the session already knows.

Backend:
- readmymind-context.ts: pure budgeted context assembler (9 ranked
  sources: pending approval dialog, user goals, last assistant turn tail,
  recent prompts, tool activity, git workspace signals, away context,
  sibling sessions, rethink state; 30 KB budget, whole-section drop from
  the bottom of the ranking, trust tiers stated in the prompt)
- readmymind-collectors.ts: transcript tail reader (the live watcher
  keeps only a 500-char snippet) and git signal collection (execFile,
  2s timeout, skipped for remote-SSH cases)
- readmymind-predictor.ts: one-shot claude -p in a throwaway tmux
  session, opus by default (readMyMindModel setting), strict JSON
  contract with 1-3 suggestions (continue / verify / redirect), newline
  stripping, 90s timeout; mutable singleton so route tests can stub it
- POST /api/sessions/:id/readmymind: claude-mode only (400), one
  prediction in flight per session (409 CONFLICT), rethink body
  { steer, rejected }; ownership via findSessionOrFail

Frontend:
- readmymind-ui.js (loadorder 11.3): header brain button, marker-hidden
  until readMyMindEnabled is ON, desktop only (phone key is phase 3);
  modal with editable suggestion + rationale and Send / Insert /
  Rethink / Dismiss; suggestion text rendered via value/textContent only
  and nothing ever auto-sends
- App Settings -> Panels checkbox for readMyMindEnabled; en + zh-CN
  strings

Verified end to end against a live isolated instance: transcript
capture, a real opus prediction grounded in the stated goals, rethink
steering, the 409, and the browser modal incl. Insert leaving the text
unsubmitted on the composer. 41 new unit/route tests; full test:ci
sweep green (4680 tests).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/web/public/readmymind-ui.js

@@ -0,0 +1,135 @@
+/**
+ * @fileoverview Read My Mind UI: predict the prompt you were about to type.
+ *
+ * A 🧠 header button (marker-hidden until the synced opt-in `readMyMindEnabled`
+ * setting is ON) opens a modal that asks the server for the user's most likely
+ * next prompt (`POST /api/sessions/:id/readmymind`, one-shot predictor over the
+ * case's intent profile + live session signals). The top suggestion lands in an
+ * editable single-line field with its rationale below; buttons are Send (with
+ * Enter), Insert (drop on the CLI composer WITHOUT Enter, for editing), Rethink
+ * (re-run with the shown suggestion recorded as rejected), Dismiss.
+ *
+ * Suggestions are NEVER auto-sent: the explicit click here is the security
+ * boundary for observed/injectable predictor inputs, so suggestion text is
+ * always rendered via value/textContent, never innerHTML. Send/Insert go
+ * server-side through `POST /api/sessions/:id/input` (UI chrome, not terminal
+ * typing, so the local-echo-overlay `sendEnterKey` trap does not apply);
+ * Send appends the `\r` that actually submits, Insert omits it.
+ *
+ * Backend: src/web/routes/readmymind-routes.ts, design: docs/readmymind-plan.md.
+ *
+ * @mixin Extends CodemanApp.prototype via Object.assign
+ * @dependency app.js (CodemanApp class, this.sessions, this.activeSessionId, showToast)
+ * @dependency settings-ui.js (loadAppSettingsFromStorage)
+ * @dependency api-client.js at runtime (this._apiJson; loads later but is only called after init)
+ * @loadorder 11.3, after panels-ui.js, before ultracode-panel.js
+ */
+
+Object.assign(CodemanApp.prototype, {
+  /** Synced setting, default OFF, opt-in via App Settings → Panels. */
+  readMyMindEnabled() {
+    return this.loadAppSettingsFromStorage().readMyMindEnabled === true;
+  },
+
+  /** Open the modal for the active session and start a prediction. */
+  openReadMyMind() {
+    const sessionId = this.activeSessionId;
+    const session = sessionId ? this.sessions.get(sessionId) : null;
+    if (!session) {
+      this.showToast('Select a session first', 'warning');
+      return;
+    }
+    if (session.mode && session.mode !== 'claude') {
+      this.showToast('Read My Mind works on Claude sessions only', 'warning');
+      return;
+    }
+    // Rethink memory resets on each open (a fresh open is a fresh question).
+    this._rmm = { sessionId, shown: null, rejected: [], busy: false };
+    document.getElementById('readMyMindModal')?.classList.add('active');
+    this._readMyMindPredict();
+  },
+
+  closeReadMyMind() {
+    document.getElementById('readMyMindModal')?.classList.remove('active');
+    this._rmm = null;
+  },
+
+  /** Run (or re-run) the prediction and render the top suggestion. */
+  async _readMyMindPredict() {
+    const state = this._rmm;
+    if (!state || state.busy) return;
+    state.busy = true;
+    this._rmmSetPhase('loading');
+
+    const body = state.rejected.length > 0 ? { rejected: state.rejected.slice(-10) } : {};
+    const data = await this._apiJson(`/api/sessions/${state.sessionId}/readmymind`, { method: 'POST', body });
+
+    // The modal may have been dismissed (or reopened for another session) while
+    // the predictor ran; drop a stale response instead of painting over it.
+    if (this._rmm !== state) return;
+    state.busy = false;
+
+    const suggestion = data && data.suggestions && data.suggestions[0];
+    if (!suggestion) {
+      this._rmmSetPhase('error');
+      return;
+    }
+    state.shown = suggestion;
+    this._rmmSetPhase('ready');
+
+    const input = document.getElementById('readMyMindPrompt');
+    const why = document.getElementById('readMyMindWhy');
+    const kind = document.getElementById('readMyMindKind');
+    // Predictor output is derived from observable (injectable) content:
+    // value/textContent only, never innerHTML.
+    if (input) input.value = suggestion.prompt;
+    if (why) why.textContent = suggestion.why || '';
+    if (kind) {
+      kind.textContent = suggestion.kind || 'continue';
+      kind.className = `readmymind-kind readmymind-kind-${suggestion.kind || 'continue'}`;
+    }
+    input?.focus();
+  },
+
+  /**
+   * Send the (possibly edited) suggestion. `withEnter` submits (`\r`, the
+   * documented single-line input rule); without it the text sits unsubmitted
+   * on the CLI composer for further editing (Insert).
+   */
+  async sendReadMyMind(withEnter) {
+    const state = this._rmm;
+    const input = document.getElementById('readMyMindPrompt');
+    const text = input ? input.value.replace(/[\r\n]+/g, ' ').trim() : '';
+    if (!state || !text) return;
+
+    const res = await this._apiJson(`/api/sessions/${state.sessionId}/input`, {
+      method: 'POST',
+      body: { input: withEnter ? `${text}\r` : text },
+    });
+    if (res === null) {
+      this.showToast('Could not reach the session', 'error');
+      return;
+    }
+    this.closeReadMyMind();
+    this.showToast(withEnter ? 'Prompt sent' : 'Inserted, press Enter in the terminal to send', 'success');
+  },
+
+  /** Re-run with the shown suggestion recorded as a rejection. */
+  rethinkReadMyMind() {
+    const state = this._rmm;
+    if (!state || state.busy) return;
+    if (state.shown && state.shown.prompt) state.rejected.push(state.shown.prompt);
+    this._readMyMindPredict();
+  },
+
+  /** Toggle the modal between its loading / ready / error phases. */
+  _rmmSetPhase(phase) {
+    const modal = document.getElementById('readMyMindModal');
+    if (!modal) return;
+    modal.querySelector('.readmymind-loading').style.display = phase === 'loading' ? '' : 'none';
+    modal.querySelector('.readmymind-result').style.display = phase === 'ready' ? '' : 'none';
+    modal.querySelector('.readmymind-error').style.display = phase === 'error' ? '' : 'none';
+    const rethinkBtn = document.getElementById('readMyMindRethink');
+    if (rethinkBtn) rethinkBtn.disabled = phase === 'loading';
+  },
+});