feat(examples/pi): adapt OpenViking extension to pi 0.81 (agent_settled commits + entry rendering)

[ZaynJarvis]

What

main already carries the full OV context-takeover extension (#3081, #3079, #3099, #3233). This PR does not re-do takeover — it adapts it to pi 0.81's new extension primitives, without regressing any existing behavior. Rebuilt on current main; single commit.

• Threshold commits no longer stall the agent run. The takeover commit (flush + commit + overview poll, worst case pollMax×pollMs ≈ 30s) previously ran inline in turn_end, blocking the in-flight run. turn_end now only accumulates token pressure (noteSynced); the commit runs from agent_settled (pi ≥ 0.81, run fully settled), with a fire-and-forget before_agent_start fallback for older pi. onTurnSynced split into noteSynced() + commitIfDue().
• ov-takeover state rendered in the TUI via registerEntryRenderer (pi ≥ 0.81): a dim one-line archive-boundary status, expandable to preview the overview; never enters LLM context. Optional, zero logic risk.
• README comparison table aligned with code (startup memory index was dropped for latency in favor of on-demand recall).

Dropped after necessity review

• mirrorMemoryWrites — mirroring .memory/MEMORY.md duplicates OV's own turn-based memory extraction (and re-mirrors unchanged content every shutdown). Removed.
• commitOnShutdown — near-dead switch (only affects non-takeover mode; takeover is on by default). Removed.

Test

• cd examples/pi-coding-agent-extension && node --test tests/*.test.mjs — 44 pass.
• End-to-end on pi 0.81.1 against a local OpenViking server: agent_settled advances the boundary 121ms after the run; pi -c restores boundary/watermark; cross-boundary facts recalled from the overview.

Note (out of scope)

DESIGN.md (pre-existing on main) still documents mirrorMemoryWrites/commitOnShutdown as implemented — a doc/code mismatch predating this PR, left for a separate cleanup.

🤖 Generated with Claude Code

https://claude.ai/code/session_01MRy5Epi4rQ7vCzSk3BLQcA

[ZaynJarvis]

closed for future PI feat migration.

[huangruiteng]

Requesting changes for one correctness race in the legacy fallback path. The focused suite passes (44/44), but a deterministic in-memory reproduction shows the boundary can advance past the data that was committed when a new prompt arrives during the overview await.

[huangruiteng]

[P1] Avoid advancing the boundary from mutable in-flight context state

This fire-and-forget call can overlap the following context hook. commitAndAdvance() awaits flush/commit/overview and only then reads mutable lastSeenUserTurns; meanwhile context can include the just-submitted user message, which has not yet been synced to OpenViking. The boundary can therefore advance past committed data and a later context transform may drop that unsynced turn. I reproduced this by starting a commit with 3 user turns and keepRecent=1, adding a fourth turn during the overview await, and observing coveredUserTurns=3 instead of the safe value 2. Please gate this fallback to runtimes without agent_settled and snapshot/derive the covered-turn count from committed state at commit start, with a regression test for the overlap.