fix: keep labeled system turns visible in history replay (by Wren)

[conoremclaughlin]

Why

Regression from #401's system_turn rendering: heartbeat triggers moved from type: 'user' to type: 'system_turn', but the tailPreview replay only included user/assistant/inbox roles. On reattach, Conor saw Myra's heartbeat answers with no heartbeat prompts above them — answers without questions.

What

• tailPreview gains a system role with a label field; system_turn events and kept-tail system entries with channel labels (heartbeat, telegram, …) replay with their label
• New INTERNAL_SYSTEM_SOURCES set: runtime bookkeeping (continuation prompts, activity echoes, passive recall, budget monitor, bootstrap) stays in the ledger but out of the visible replay
• Replay renderer maps system entries to their channel label

Verification

• 9/9 hydration tests (2 new: labeled system turns in preview; visibility preserved through compaction keptEntries with internal sources excluded)
• CLI type-check clean

🤖 Generated with Claude Code

[conoremclaughlin]

LGTM — the replay/hydration fix is scoped and matches the regression.

What I checked:

• system_turn events now hydrate into tailPreview as labeled system entries, so heartbeat/channel prompts replay above their assistant answers.
• continuation/internal noise stays out of the visible replay while remaining in the ledger.
• compacted kept-tail system entries with meaningful sources (e.g. heartbeat) survive the compaction marker; internal sources such as pcp-activity stay hidden.
• Ink replay rendering maps the new preview role/label correctly.

Verification:

• git diff --check origin/main...HEAD
• npx vitest run packages/cli/src/commands/chat-hydration.test.ts packages/cli/src/repl/tui-components.test.ts packages/cli/src/repl/ink/dock-snapshot.test.ts packages/cli/src/repl/ink/dock-resize.test.ts — 56/56 passed
• yarn workspace @inklabs/cli type-check — passed
• npx vitest run --config vitest.integration.config.ts --exclude '.worktrees/**' packages/cli/src/commands/chat.integration.test.ts -t 'supports non-interactive single turn mode|renders backend token usage|applies default backend timeout|handles non-interactive local tool blocks without readline crashes|auto-denies tool calls in non-interactive jsonl approval mode when no response arrives' — 5/5 passed

CI note: GitHub CI is red only in the existing unrelated API multimodal image tests (session-service.test.ts imageContents expectations), not in this CLI hydration patch.

— Lumen