fix(smart): routing coherence + enrichment latency (nearestHeading quadratic blowup)

[protostatis]

Follow-up to #48, from a live 24-site out-of-matrix evaluation of the smart MCP surface.

Root cause of the enrichment-timeout epidemic

nearestHeading() in src/js/page_model.js ran querySelector('h1..h4') over each ancestor's entire subtree for every link — O(links × depth × doc size) on QuickJS, blowing the 30s eval watchdog (route_discover: InternalError: interrupted). discover swallowed the error and returned empty after exactly 30s; the Python layer's 6–8s budget then reported timeout escalation. Affected ~30% of mainstream sites (HN, CNN, Verge, MDN, Yahoo Finance, docs.rs, Lobsters…).

Fix: scan only direct children at each ancestor level (also better semantics: own-section heading). lobste.rs route_discover 30.0s → 0.04s; matrix timeout escalations 7/24 → 0; BBC end-to-end 25.9s → 1.7s.

Routing-coherence fixes

• thin_shell contradiction (crates.io, old.reddit): escalation suggested extract while avoid[] forbade it. Now gated on json_scripts > 0, else suggests query_debug.
• New _apply_coherence(): no next_tools/micro_hint entry may contradict avoid[]; defense in depth against any future branch drift.
• Challenge confidence floor: sub-0.7 challenge matches no longer shadow a concrete HTTP status (httpbin 503 was challenge@0.55); kept as challenge_shadowed evidence.

Efficiency / robustness

• Enrichment phase gets one shared deadline instead of k sequential budgets (Client.call is synchronous request/response — true parallelism would cross-read responses).
• Cards run before discover so a slow call starves routes, not content.
• bundle.raw slimmed to the six fields drivers read (~2× token cut per open()).
• Guarded controls[0] IndexError on forms with no controls (eBay error page).

Verification

• 5 new fixture tests (thin_shell gating, challenge floor, coherence filter, find-binary mtime rule lives in the follow-up PR); full suite 9/9.
• cargo test --release: 128/128.
• Live 24-site matrix before/after: flags 5 → 0, timeout-esc 7 → 0, enrichment populated on all content pages.

[protostatis]

Sky's Code Review

This PR fixes a real production bug (O(links × depth × doc size) nearestHeading blowup causing 30s watchdog timeouts) and adds sensible routing-coherence fixes (thin_shell/extract contradiction, challenge confidence floor, _apply_coherence defense-in-depth). The nearestHeading rewrite to direct-children scanning is correct and a dramatic performance win. The escalation logic for challenge_shadowed is actually safe from NameError on all traced paths, and the confidence-floor change is reasonable. Main concerns: (1) the find_binary test_added-without-implementation mismatch, (2) the shared-deadline implementation can still overrun the budget because each call gets a min-0.5s floor even after the deadline passes, and (3) the timeout path doesn't actually cancel the synchronous Client.call, so a timed-out call can still cross-read responses on the single pipe the PR itself warns about.

Verdict: Comment

Comments

• The nearestHeading change is correct and the semantics shift (own-section heading) is intentional and well-motivated. Confirmed the iterator now scans n.children (element-only) per ancestor level, which is O(depth × child-count) instead of subtree querySelector — matches the reported 30.0s → 0.04s.
• Bundle 'raw' slimming to six fields is a good token reduction, but it silently changes raw from the full navigate result to a partial view. If any driver/routing consumer reads a field outside those six (e.g. blockmap, extract, headers that were previously present in raw), it will now KeyError or get None. The six-field list is a reasonable contract but should be documented as the canonical surface for raw.
• The challenge confidence floor (conf >= 0.7 or not http_error) is a sound calibration fix and the shadowed-evidence preservation is good. Note the default conf=0.9 when confidence is absent means a challenge with no confidence field still preempts any HTTP error status — likely intended, but worth confirming that's the desired behavior for unknown detectors.

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Reviewed by Sky — Unchained Sky engineering agent

[protostatis]

remaining = max(0.5, deadline - time.monotonic()) gives every enrichment call a 0.5s floor even after the shared deadline has fully expired. With 3 specs, the phase can overrun the budget by ~1.5s (plus whatever a single in-flight call already consumed). If the hard budget must be honored, clamp instead with if remaining <= 0: break rather than flooring to 0.5, or at least cap the floor so only the first call after expiry gets a grace period.

[protostatis]

fut.cancel() on a ThreadPoolExecutor future rarely interrupts the running self.call (threads can't be killed), so the synchronous request/response over the single pipe continues in the background. The very next _timed_call submits a new self.call, and per this PR's own comment ('no id matching, so concurrent calls would cross-read responses') that timed-out-but-still-running call can cross-read the next response. The shared deadline shrinks the window but doesn't eliminate it. Consider guarding the pool/pipeline with a lock or draining/awaiting the timed-out future before the next submit.

[protostatis]

challenge_shadowed is only bound when challenge is truthy AND conf < 0.7 AND http_error. It is correctly guarded (the later if challenge short-circuits when falsy, and all fall-through paths assign it), so no NameError today — but the binding is implicit and spread across two branches. Worth a one-line comment noting the invariant, since any future sub-branch added inside if challenge: could silently leave it unbound.

[protostatis]

test_find_binary_prefers_freshest_local_build asserts find_binary() prefers the freshest binary by mtime, but the PR description explicitly states 'find-binary mtime rule lives in the follow-up PR' and this diff contains no change to find_binary (only smart.py and page_model.js). As written this test will fail against the current code. Either ship the find_binary change here or move the test to the follow-up PR.

[protostatis]

All four addressed in bb8aed2:

1. 0.5s floor overrun — dropped. remaining <= 0 now skips outright with a skipped: budget exhausted error instead of flooring.

2. Cross-read after timeout — the real one, fixed properly: _timed_call now returns (result, future). On timeout the loop gives the abandoned worker a 1.5s grace to land its response (a recovered result is used); if it doesn't finish, remaining specs are skipped with skipped: … rpc pipe reserved and the phase breaks — no further submit can misread another call's reply. Residual exposure is now only cross-invocation (next tool call racing a zombie), which needs the id-matched reader noted as the v2 client fix; in-phase it's closed.

3. challenge_shadowed invariant — documented at the binding with an explicit warning for future early-returns inside the challenge block.

4. Misplaced test — you're right, that was my branch split leaking. test_find_binary_prefers_freshest_local_build moved to fix(packaging): find_binary prefers freshest local build over stale bundled binary #51 (46c0b54) where its fix lives; this branch is back to 8/8 standalone-green.

Re-verified after changes: pytest 8/8 here, 6/6 on #51.

[protostatis]

Sky's Code Review

Well-executed follow-up addressing two real production issues: the O(links×depth×doc-size) nearestHeading quadratic blowup causing 30s eval watchdogs, and routing-coherence contradictions (thin_shell suggesting extract while avoid[] forbids it). The challenge-confidence floor correctly fixes httpbin 503 being misclassified as challenge@0.55, and the shared-deadline enrichment phase is a sensible design given the synchronous single-pipe RPC. The challenge_shadowed binding is currently correct but relies on a documented invariant that is fragile to future edits. Tests are thorough (5 fixtures + full suite). Overall the changes are correct with no security or production-breaking bugs.

Verdict: Approve

Comments

• The invariant-comment approach for challenge_shadowed is a code smell that will bite during future branch edits; prefer structural safety (initialize to None, or return a sentinel) over prose.
• The shared-deadline comment says calls stay sequential (no true parallelism) — correct given position-matched response reads, and the cards-before-discover ordering is a good call so slow discover starves routes, not content.

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Reviewed by Sky — Unchained Sky engineering agent

Inline Comments (could not attach to lines)

python/unbrowser/smart.py:405 — The challenge_shadowed binding is correct today but is fragile: it is only assigned in the low-confidence+HTTP-error branch, then spread into {**shadow, ...} later. Any future early-return added inside the if challenge: block before that assignment will raise UnboundLocalError at the HTTP-error section. The comment documents this, but a more robust pattern would be to initialize challenge_shadowed = None before the if challenge: block and build shadow conditionally on is not None. Consider a structural guarantee (init to None) over a comment guarantee.

python/unbrowser/smart.py:744 — The 1.5s grace drain (fut.result(timeout=1.5)) can push total phase time ~1.5s past the stated shared timeout budget, since the abandoned worker owns the pipe. This is necessary to avoid cross-reading responses, but the effective worst case is timeout + 1.5s, not timeout as the PR description implies (BBC 26s → 1.7s still holds for the happy path, but the bounded-worst-case claim is slightly off). Worth a one-line doc note so future readers don't assume a hard timeout ceiling.

python/unbrowser/smart.py:576 — In _apply_coherence, when bundle.get("next_tools") is None/unset and avoid_tools is non-empty, nxt becomes [] and [] != None is True, so bundle["next_tools"] is set to an empty list rather than left unset. This is almost certainly harmless, but if any downstream consumer branches on next_tools is None vs next_tools == [], this mutation changes semantics. Confirm no consumer distinguishes these; otherwise initialize carefully.

src/js/page_model.js:186 — Nice fix and the direct-children semantics are arguably more correct (own-section heading). One behavior note: n.children returns only element nodes, so text-only heading wrappers (unusual) are skipped, and the loop terminates correctly on Document nodes via the n.tagName guard. No issue — just flagging that <h1 itemprop="name"> with a child element (e.g. <span>) inside the heading will still match on the itemprop branch since k is the heading element itself. Looks correct.