docs: add session activity plan

[moose-lab]

Summary

• Add the Session Agent Activity Stream implementation plan under docs/superpowers/plans/.
• Keep this as a documentation-only follow-up after the Issue 让运行中的任务成为双向控制面：既能看到阶段进度，又能在需要人工确认的关卡介入 #37 control-plane work.

Test Plan

• git diff --cached --check
• bun run typecheck
• TZ=Asia/Shanghai bun run test (224 passed)

[claude]

Code Review

• Gather context
• Read changed file
• Review document

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[claude]

Claude finished @moose-lab's task in 1m 24s —— View job

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Code Review

• Gather context
• Read changed file
• Review document

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Documentation-only plan for the session activity stream feature. Well-structured with clear task breakdown, test-first approach, and explicit checkpoints. A few issues to address before implementation begins.

Findings

• [must-fix] Task 1, Step 1 — test assertion vs. fixture mismatch (docs/superpowers/plans/2026-06-03-session-agent-activity-stream.md:68–103): The session INSERT does not include a started_at column, so it will be NULL in the DB. But the assertion at line 96–103 expects started_at: "2026-06-03 00:41:14". The replay helper queries started_at directly from the sessions table, so this assertion will fail on first run. Fix: either add started_at to the INSERT ('2026-06-03 00:41:14'), or update the assertion to expect null. Fix this →

• [should-fix] Task 4, Step 3 — nextId() is unspecified (docs/superpowers/plans/2026-06-03-session-agent-activity-stream.md:574): nextId() is called inside appendActivity but never defined or imported. If an implementor picks Date.now(), millisecond collisions are possible under fast replay. Recommend defining it explicitly as a useRef counter: const idRef = useRef(0); const nextId = useCallback(() => ++idRef.current, []);.

• [nit] Task 2, Step 1 — overly broad catch {} (docs/superpowers/plans/2026-06-03-session-agent-activity-stream.md:289–291): The comment says // DB might not be ready, but the catch swallows all errors from the entire replay loop, including programming errors (e.g., a bad SQL query). Consider narrowing to log unexpected errors: catch (err) { if (!(err instanceof DatabaseError)) console.error('replay error', err); }.

• [nit] Task 4, Step 4 — TerminalIcon import not specified (docs/superpowers/plans/2026-06-03-session-agent-activity-stream.md:663): TerminalIcon is used in ActivityTimeline but the plan doesn't show where it's imported from. Since the project uses lucide-react elsewhere, this is likely import { Terminal as TerminalIcon } from "lucide-react", but the plan should make this explicit to avoid ambiguity.

Verdict: COMMENT