fix(api): bound indexed queue read amplification

[tom-sapletta-com]

Ticket: PLF-10675
Correlation ID: planfile-index-read-pressure

Outcome

• coalesce concurrent filesystem signature scans behind a 250 ms bounded cache
• invalidate the cache before and after every local mutation and probe active-queue changes cheaply
• pass one exact source signature through each indexed request instead of rescanning it repeatedly
• render operational queue pages inside SQLite JSON rather than materializing thousands of Python object graphs
• preserve bounded stale-index reads with accurate result-count headers

Evidence

• 402 passed, 6 skipped
• focused concurrency and operational projection regression tests
• ruff check and compileall pass
• live canary on the preceding merge reproduced 50/50 timeouts, providing the failure baseline this PR addresses

Authority

Bounded local/runtime repair for PLF-10675. Exact-head Validator approval and protected merge are required.

[ifuri-validator-agent]

Deterministic Validator approval for exact head de2272db3dbeb58dbeea9894014450c70b01d42e.

Ticket: PLF-10675
Correlation ID: planfile-pr-44-PLF-10675
Model: zai/glm-5.3
Reviewed diff chunks: 2
Advisory LLM verdict: APPROVE
Advisory summary: Reviewed all 2 diff chunk(s). Chunk adds a TTL-bounded (250ms, capped at 3s) process-local signature cache invalidated on both sides of the mutation lock, threads the exact signature through indexed list responses, and moves the operational view projection into SQLite's JSON runtime (_remove on whitelisted paths) to avoid materializing large Python object graphs. Tests pass and no security issues were found. | Chunk adds an optional signature parameter to avoid redundant filesystem scans, a new SQLite-rendered operational response path, and concurrency/invalidation tests. Logic is consistent and tests cover coalescing, invalidation, and rendering. No issues visible in this chunk.
Advisory findings: none
The LLM output above is advisory and was not used as the approval trust root.
Merge will be attempted after this approval when explicitly authorized.

Decision record (recomputable)

DECISION D-675-5829
TICKET PLF-10675
HEAD_SHA de2272db3dbeb58dbeea9894014450c70b01d42e
CORRELATION_ID planfile-pr-44-PLF-10675
ACTOR agent:ifuri-validator-agent[bot]
APPLIED_RULE P-CORE-015
INPUT author_login = "tom-sapletta-com"
INPUT observed_checks = ["notify=PASS","ci-loop=PASS"]
INPUT required_checks = ["ci-loop","notify"]
INPUT required_checks_source = "protected registry (env/request)"
INPUT reviewer_login = "ifuri-validator-agent[bot]"
INPUT superseded_checks = []
VERDICT APPROVE AUTHORITY DETERMINISTIC
REJECTED REQUEST_CHANGES BECAUSE NO_UNSAFE_CHANGE_REASON_FOUND
ADVISORY llm_verdict = "APPROVE" MODEL "zai/glm-5.3"
ASSERT VERDICT_AUTHORITY != "ADVISORY"