fix(kpi): reject malformed threshold input bytes

[seonghobae]

Purpose

Test-first repair for #126. KPI threshold and window checks must fail closed on malformed retained UTF-8 rather than calculate PASS/FAIL metrics from replacement-decoded bytes.

Exact current identity

• protected/live base: main c85d710804139c0697d7ef8fa47d02b1389e6d84;
• branch: fix/check-kpi-fatal-utf8;
• RED head: 85a9ce68f346a4281b539bcc45df607a6e4ea66d;
• GREEN/current head: 85463e4e18750af27aac8ea35ee1680e7b360661;
• current compare: 2 commits ahead / 0 behind main, merge base exactly the live protected head;
• changed paths: scripts/check-kpi.mjs, test/check-kpi-input-integrity.test.ts.

RCA -> RED -> GREEN

Protected scripts/check-kpi.mjs used await fs.readFile(inputPath, "utf8"), so malformed retained bytes could be replacement-decoded before JSON parsing. A byte-invalid /exchange record could therefore influence failure-rate, p95 latency and required-window semantics.

The RED regression injects malformed UTF-8 into an otherwise valid /exchange record and requires a non-zero result before metric output. A separate valid fixture pins existing threshold semantics and the policy of ignoring syntactically non-JSON/non-Noema lines.

GREEN reads exact bytes and decodes with TextDecoder("utf-8", { fatal: true }) before line, JSON or time-window semantics. Malformed bytes fail closed without KPI output. Threshold, route, latency and timestamp behavior are otherwise unchanged.

Exact current-head proof

For unchanged current head 85463e4e18750af27aac8ea35ee1680e7b360661:

• application ci 31443518948: terminal success;
• reviewer-ci 31443518901: terminal success;
• eligible central Security Scan 31443518918: terminal success;
• formal reviews: 0;
• inline review threads: 0;
• GitHub reports the PR Ready and mergeable.

CodeRabbit was rate-limited on this exact base/head; that is non-passing review evidence and not approval.

Dependency / authority boundary

This is distinct from #122/#123 (kpi:compute) and #104/#105 (strict provenance/snapshot orchestration). Exact-byte provenance does not make lossy semantic decoding safe, and this PR does not modify #105's branch. It does not establish real production KPI provenance or a 30-day operating window, publish a release, deploy, select an outbound license, or create acquisition-readiness evidence. Technical GREEN cannot replace live #27 governance or qualifying independent non-author formal approval under #29.

Related: #3, #27, #29, #104, #105, #122, #123, #126

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Review details

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Configuration used: Organization UI

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Run ID: e8a23aff-6f73-4bd6-a41e-3a9d7402ef9c

📥 Commits

Reviewing files that changed from the base of the PR and between c85d710 and 85463e4.

📒 Files selected for processing (2)

• scripts/check-kpi.mjs
• test/check-kpi-input-integrity.test.ts

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