refactor: extract TabSession for per-tab state isolation (v0.15.16.0) (#873)

* plan: batch command endpoint + multi-tab parallel execution for GStack Browser

* refactor: extract TabSession from BrowserManager for per-tab state

Move per-tab state (refMap, lastSnapshot, frame) into a new TabSession
class. BrowserManager delegates to the active TabSession via
getActiveSession(). Zero behavior change — all existing tests pass.

This is the foundation for the /batch endpoint: both /command and /batch
will use the same handler functions with TabSession, eliminating shared
state races during parallel tab execution.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* refactor: update handler signatures to use TabSession

Change handleReadCommand and handleSnapshot to take TabSession instead of
BrowserManager. Change handleWriteCommand to take both TabSession (per-tab
ops) and BrowserManager (global ops like viewport, headers, dialog).
handleMetaCommand keeps BrowserManager for tab management.

Tests use thin wrapper functions that bridge the old 3-arg call pattern to
the new signatures via bm.getActiveSession().

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* feat: add POST /batch endpoint for parallel multi-tab execution

Execute multiple commands across tabs in a single HTTP request.
Commands targeting different tabs run concurrently via Promise.allSettled.
Commands targeting the same tab run sequentially within that group.

Features:
- Batch-safe command subset (text, goto, click, snapshot, screenshot, etc.)
- newtab/closetab as special commands within batch
- SSE streaming mode (stream: true) for partial results
- Per-command error isolation (one tab failing doesn't abort the batch)
- Max 50 commands per batch, soft batch-level timeout

A 143-page crawl drops from ~45 min (serial HTTP) to ~5 min (20 tabs
in parallel, batched commands).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* test: add batch endpoint integration tests

10 tests covering:
- Multi-tab parallel execution (goto + text on different tabs)
- Same-tab sequential ordering
- Per-command error isolation (one tab fails, others succeed)
- Page-scoped refs (snapshot refs are per-session, not global)
- Per-tab lastSnapshot (snapshot -D with independent baselines)
- getSession/getActiveSession API
- Batch-safe command subset validation
- closeTab via page.close preserves at-least-one-page invariant
- Parallel goto on 3 tabs simultaneously

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* fix: harden codex-review E2E — extract SKILL.md section, bump maxTurns to 25

The test was copying the full 55KB/1075-line codex SKILL.md into the fixture,
requiring 8 Read calls just to consume it and exhausting the 15-turn budget
before reaching the actual codex review command. Now extracts only the
review-relevant section (~6KB/148 lines), reducing Read calls from 8 to 1.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* docs: move batch endpoint plan into BROWSER.md as feature documentation

The batch endpoint is implemented — document it as an actual feature in
BROWSER.md (architecture, API shape, design decisions, usage pattern)
and remove the standalone plan file.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* chore: bump version and changelog (v0.15.16.0)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: gstack <ship@gstack.dev>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

browse/test/commands.test.ts

@@ -9,14 +9,20 @@ import { describe, test, expect, beforeAll, afterAll } from 'bun:test';
 import { startTestServer } from './test-server';
 import { BrowserManager } from '../src/browser-manager';
 import { resolveServerScript } from '../src/cli';
-import { handleReadCommand } from '../src/read-commands';
-import { handleWriteCommand } from '../src/write-commands';
+import { handleReadCommand as _handleReadCommand } from '../src/read-commands';
+import { handleWriteCommand as _handleWriteCommand } from '../src/write-commands';
 import { handleMetaCommand } from '../src/meta-commands';
 import { consoleBuffer, networkBuffer, dialogBuffer, addConsoleEntry, addNetworkEntry, addDialogEntry, CircularBuffer } from '../src/buffers';
 import * as fs from 'fs';
 import { spawn } from 'child_process';
 import * as path from 'path';
 
+// Thin wrappers that bridge old test calls (bm as 3rd arg) to new signatures (session + bm)
+const handleReadCommand = (cmd: string, args: string[], b: BrowserManager) =>
+  _handleReadCommand(cmd, args, b.getActiveSession());
+const handleWriteCommand = (cmd: string, args: string[], b: BrowserManager) =>
+  _handleWriteCommand(cmd, args, b.getActiveSession(), b);
+
 let testServer: ReturnType<typeof startTestServer>;
 let bm: BrowserManager;
 let baseUrl: string;