spec(contributor-scan): record the honest end-to-end tuning of 7.8

Four interacting defects surfaced in sequence when the portioner was measured end to end, each
hidden by the one before: run_batch timing polluted by its own retry, a single-attempt path missing
on the partitioned graph every plugin uses, and killed remainders dropped by a fixed chunk list. All
fixed and unit-tested; the end-to-end completion number is re-measuring on a frozen tree.

Co-Authored-By: Claude Opus 4.8 <[email protected]>
Claude-Session: https://claude.ai/code/session_01EmM1j46qgKMh3zqD1QMwEo

.kiro/specs/contributor-scan/tasks.md

@@ -1284,6 +1284,7 @@ the ontology describes libraries, frameworks and language constructs, never repo
   - _Status 2026-09-22:_ implemented; host controls pass for the assembler in both forms and under a kill, for the remainder-only retry, and for the sizer; the joern-gated check passes on the real engine — the taint query streams one line per request, and the comment-sink and literal-destination controls hold under the streamed form. The plugin measurement is running on a frozen export of the committed source.
   - _Two things the measurement exposed on the way, both fixed:_ the evidence pass was one unportioned batch protected only by the ceiling — 22,125 requests on a plugin push transaction — and now runs in portions of 4,000; and a first cut of the harvest read a timed-out process's pipe BEFORE killing it, which blocks forever because a pipe whose writer is alive never reaches end-of-file. The suite's own hanging-engine control caught that after twenty minutes of what I mistook for CPU starvation.
   - _A stated limit:_ the reuse layer's re-query of `missing` ids calls the backend batch directly and so bypasses sink-weighted portioning. Those re-queries are the small remainder of a cached scan, and streaming still keeps what a killed one finished, so it is recorded here rather than fixed.
+  - _End-to-end tuning, 2026-09-23, the honest version._ The first end-to-end run REGRESSED completion (64 of 406 against 7.7's 153) while finding as many defects, and each fix exposed the next: the adaptive sizer read one portion at 953 s because it timed `run_batch`, whose own split-retry folded in, and collapsed; giving the portioner a single-attempt path (`run_batch_once`) fixed the timing but only after it was wired on the PARTITIONED graph too, which every plugin uses and which the first wiring missed; and even then completion sat at 56 of 406 because the portioner iterated a fixed list and dropped the remainders of killed portions, stopping at 1,263 s of a 3,600 s budget. The queue re-asks those remainders. The sizer now adapts both ways in the trace — 268 up to 535 after a cheap portion, halved to 267 to 133 on kills — and re-asks what a kill left. Each step is unit-tested: the assembler in both forms and under a kill, the single-attempt path, coverage-halving, and queue termination. The end-to-end completion number is being re-measured on a frozen tree; findings rose to 141 and the declared target is detected under the streamed form.
   - _Boundary: cpg backend, contributor-scan scan budget, taint query_
   - _Depends: 7.7_
   - _Requirements: 4.1, 6.3, 8.1_