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/server.ts

@@ -87,6 +87,7 @@ import {
 } from './session-listener-wiring.js';
 import { sessionWaits, hooksAvailableForMode } from './session-wait-registry.js';
 import { intentStore } from '../intent-store.js';
+import { AI_CHECK_MODEL } from '../config/ai-defaults.js';
 import { approvalInbox } from './approval-inbox.js';
 import {
   wireRespawnListeners,
@@ -639,6 +640,8 @@ export class WebServer extends EventEmitter {
       getLightSessionsState: this.getLightSessionsState.bind(this),
       startTranscriptWatcher: this.startTranscriptWatcher.bind(this),
       stopTranscriptWatcher: this.stopTranscriptWatcher.bind(this),
+      getTranscriptPath: (sessionId: string) => this.transcriptWatchers.get(sessionId)?.getPath() ?? null,
+      getReadMyMindModel: this.getReadMyMindModel.bind(this),
       // InfraPort
       mux: this.mux,
       runSummaryTrackers: this.runSummaryTrackers,
@@ -1696,6 +1699,18 @@ export class WebServer extends EventEmitter {
     return settings.agentSkillEnabled === true;
   }
 
+  /**
+   * Read My Mind predictor model (docs/readmymind-plan.md): `readMyMindModel`
+   * setting, defaulting to the AI-checker opus model. Prediction quality is
+   * the product and runs only on an explicit press, so the cost profile is
+   * nothing like the idle checker's.
+   */
+  private async getReadMyMindModel(): Promise<string> {
+    const settings = await this.readSettings();
+    const model = typeof settings.readMyMindModel === 'string' ? settings.readMyMindModel.trim() : '';
+    return model || AI_CHECK_MODEL;
+  }
+
   // Helper to get model configuration from settings
   private async getModelConfig(): Promise<{
     defaultModel?: string;