fix(scope-coherence): isolate implementation depth counter per session

[brianjones-v4n]

Summary

• State schema change: implementationDepth, sessionStart, sessionDocsRead, and related fields move from top-level keys to per-session entries under a new sessions map, keyed by INSTAR_SESSION_ID (with a manual-{pid} fallback for terminal sessions).
• Each session starts at depth 0 — counters no longer bleed across sessions. A prior session that accumulated depth 16 won't cause a new session to trip the checkpoint after only 4 actions.
• Concurrent sessions are fully isolated — two sessions running simultaneously each track their own depth independently.
• Cooldown and dismissal tracking remain global — these prevent excessive nagging, and nagging across sessions is still nagging. Doc comments annotate this intent so the next reader doesn't try to "fix" it.
• Old sessions auto-pruned — when more than 10 session entries accumulate, the oldest are dropped on the next write (MAX_SESSION_ENTRIES = 10).

Problem

The scope-coherence hooks used a single global implementationDepth counter in .instar/state/scope-coherence.json. The counter was set once (if (!state.sessionStart)) and never reset between sessions. A prior session that accumulated depth 16 would leave the counter at 16, and the next session would trip the 20-action threshold after only 4 Edit/Write/Bash calls — producing a spurious "SCOPE COHERENCE CHECK" block.

Additionally, concurrent sessions in the same project would share the same counter, causing cross-session interference: session A's writes could trip session B's checkpoint.

Files changed

• .instar/hooks/instar/scope-coherence-collector.js — PostToolUse hook, tracks tool actions
• .instar/hooks/instar/scope-coherence-checkpoint.js — Stop hook, triggers scope zoom-out
• src/core/PostUpdateMigrator.ts — Template methods that generate the hook files on install

Design Decisions

1. Session ID from INSTAR_SESSION_ID — set by the Instar server for spawned sessions. Falls back to manual-{pid} for terminal sessions.
2. MAX_SESSION_ENTRIES = 10 — named constant with inline comment, not a magic number.
3. Global cooldown — annotated "prevents nagging across sessions" so the next reader understands the intentional asymmetry.
4. Backward compatible — old flat-key state files are ignored by the new code. No migration needed.

Repro

A real-world hit: a fresh agent session got blocked by SCOPE COHERENCE CHECK after only ~4 tool actions. Inspection of .instar/state/scope-coherence.json showed implementationDepth: 16 left over from a prior session's work earlier in the day.

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[JKHeadley]

Echo's Review — PR #133

Recommendation: merge (pending @JKHeadley approval — touches .instar/hooks/)
Value: moderate | Strategy: comment-only

Summary

This is a well-scoped fix for a real bug: a global implementationDepth counter in scope-coherence.json was bleeding across sessions, causing fresh sessions to trip the 20-action checkpoint after only ~4 tool calls. The PR moves per-session state under a new sessions map keyed by INSTAR_SESSION_ID, with manual-{pid} fallback for terminal sessions. Cooldown and dismissal counts are intentionally kept global (preventing nag-storms across sessions), with explanatory comments on the asymmetry.

Strengths

• Real bug, real repro — the scope-coherence false-trip is something we've hit too; the inline state inspection (implementationDepth: 16 carryover) matches the failure mode.
• Touches both source-of-truth files — runtime hooks (.instar/hooks/instar/*) AND the PostUpdateMigrator.ts template that generates them on update. Skipping the template would silently regress the fix on the next install.
• Backward-compatible state shape — old flat-key state is ignored cleanly; loadState returns { sessions: {} } and the next write overwrites with the new shape. No migration needed.
• Bounded growth — MAX_SESSION_ENTRIES = 10 with newest-first pruning prevents the sessions map from accumulating indefinitely.
• Headless-job carve-out — the new INSTAR_SESSION_ID && !TERM_PROGRAM early-approve in the checkpoint hook avoids blocking unattended sessions where there's no human to dismiss the prompt.
• Comments explain intent — the global-vs-per-session asymmetry is annotated so a future reader doesn't "fix" it.

Concerns

• No regression test for the new behavior (severity: moderate). The repo has integration/e2e tests for the scope-coherence API routes but not the hook scripts themselves, so this PR doesn't break any existing test, and it follows the prevailing pattern for hook coverage. Still, a small unit/integration test that drives the collector with two synthetic INSTAR_SESSION_IDs and asserts depth isolation would lock in the fix and catch future regressions.
• Concurrent file writes are not atomic (severity: minor). loadState → mutate → saveState is racy if two sessions' PostToolUse hooks fire at the same instant. The prior global counter had the same race, but per-session isolation slightly increases the surface (a session can lose its first depth increment if another session writes between load and save). Worst case is the threshold takes longer to hit — not a correctness disaster, but worth noting.
• TERM_PROGRAM heuristic for headless detection is fragile (severity: minor). Custom terminals or some shell setups may not set TERM_PROGRAM, in which case interactive sessions would be treated as headless and skip the checkpoint entirely. A more durable signal (e.g., presence of stdin TTY, or an explicit INSTAR_HEADLESS flag set by the spawner) would be more robust. Acceptable for v1 if the intent is "best-effort silencing for jobs."

Test Coverage

No new tests. Existing API-route tests still pass (and remain unaffected — they don't exercise the hook scripts). The hook scripts themselves have always been untested in this repo, so this PR doesn't regress coverage but doesn't improve it either. Recommend a follow-up to add a small harness that pipes JSON to the collector hook and verifies the per-session state shape.

Verdict

The fix is correct, scoped, and well-explained. The only structural blocker is policy: this PR modifies .instar/hooks/, which our review policy classifies as security-critical and requires explicit @JKHeadley approval — Echo cannot approve. Once Justin signs off, this is safe to merge as-is. The follow-up I'd want to see (regression test for per-session isolation) can land separately.

Next Steps

• @JKHeadley to review and approve (security-path policy requires human approval)
• Optional follow-up PR: a small test that drives the collector with two INSTAR_SESSION_ID values and asserts depth isolation + pruning at MAX_SESSION_ENTRIES

Thanks @brianjones-v4n — clean diff, clear repro, correct dual-update across the runtime hook and the migrator template. Appreciated.

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Automated review by Echo — instar's developer agent. This review was generated by an AI system. For questions or concerns, please tag @JKHeadley.

[JKHeadley]

Stage 2 Deep Review — Recommend Merge

Reviewer: Echo (AI) — automated deep review, not an approval. Human maintainer decision required.

Summary

Tight, well-targeted fix for the false-positive scope-coherence checkpoint. The diagnosis (one global implementationDepth accumulating across sessions) matches the symptom (fresh sessions tripping the 20-action threshold after ~4 actions). Per-session keying is the right structural fix.

What I verified

• Live hook ↔ template parity. The new logic lands in three places — scope-coherence-collector.js, scope-coherence-checkpoint.js, and the corresponding string templates inside PostUpdateMigrator.ts. Spot-checked the migrator output: both the headless-session bypass (INSTAR_SESSION_ID && !TERM_PROGRAM → approve) and the sessions: {} shape are present in the template, so fresh installs will get the same behavior as the live hooks. No drift.
• Session ID source. INSTAR_SESSION_ID is set by the server for spawned sessions; manual-{pid} is a reasonable fallback for terminal sessions. PID reuse is a theoretical concern but bounded by MAX_SESSION_ENTRIES = 10 pruning plus the per-session 5-min settle window, so a stale reused entry can at worst delay one nag — not block.
• Global vs per-session split. Cooldown (lastCheckpointPrompt) and dismissal counter remain global, intentionally — preventing nag flood across sessions. The inline comment annotates this so a future reader doesn't "fix" it. Good.
• Headless bypass. New: server-spawned/job sessions skip the block entirely (no TTY to show the message to). Correct — previously they'd silently lose tool actions to a UX prompt nobody could see.
• Pruning. pruneSessions() sorts by sessionStart descending and drops the tail past 10. Stable, no unbounded growth.
• CI. All shards green on Node 20/22, Integration, E2E, Build. Vercel "failure" is an auth state, not a build failure.

Security / injection scan

No prompt-injection or instruction-override patterns in the diff. State-file I/O is wrapped in try/catch and writes a plain JSON object; no untrusted-content interpolation.

Non-blocking observation

The PR ships hook-script logic with no automated regression test. The change is simple enough that CI passing is a meaningful signal, but a unit test that simulates two concurrent sessions hitting the collector (and asserting they don't trip each other's counters) would prevent re-regression. Suggest as a follow-up, not a blocker.

Recommendation

Safe to merge. Internally consistent (live hook + template), behaviorally minimal for the happy path, fixes a real false-positive that's been observed in the wild. Thanks @brianjones-v4n.

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🤖 Stage 2 review by Echo. AI agents do not approve PRs — final merge decision belongs to a human maintainer.