fix(kpi): reject malformed direct KPI input bytes

[seonghobae]

Purpose

Test-first repair for #122. The direct kpi:compute operator must not calculate metrics from replacement-decoded malformed UTF-8 bytes.

Exact current identity

• protected/live base: main c85d710804139c0697d7ef8fa47d02b1389e6d84;
• branch: fix/compute-kpi-fatal-utf8;
• RED head: bef6d16f9c99da7a460e755dd51dc5aa0d9a7a2c;
• GREEN/current head: b93db0492bfe60866504a77aff2fea809fae732d;
• current compare: 2 commits ahead / 0 behind main, merge base exactly the live protected head;
• changed paths: scripts/compute-kpi.mjs, test/compute-kpi-input-integrity.test.ts.

RCA -> RED -> GREEN

Protected scripts/compute-kpi.mjs used fs.readFileSync(inputPath, "utf8"), so malformed retained bytes could be replacement-decoded before NDJSON parsing. A byte-invalid /exchange record could therefore still contribute to request, failure and latency metrics.

The RED regression writes that exact byte-invalid shape and requires non-zero process status, no metric output and an explicit invalid-UTF-8 diagnostic. A separate valid fixture pins existing metric behavior and the policy of ignoring syntactically non-JSON lines.

GREEN reads exact bytes and decodes them with TextDecoder("utf-8", { fatal: true }) before line or JSON semantics. Malformed text fails closed before metric computation. Existing route/status/latency semantics are unchanged.

Exact current-head proof

For unchanged current head b93db0492bfe60866504a77aff2fea809fae732d:

• application ci 31443094646: terminal success;
• reviewer-ci 31443094668: terminal success;
• eligible central Security Scan 31443094743: 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 model/review evidence and not approval.

Authority boundary

This changes only the direct KPI computation input-decoding boundary. It does not establish production provenance, prove a 30-day KPI window, modify #105's strict provenance/snapshot work, publish a release, deploy, select an outbound license, or create acquisition-readiness evidence. Technical GREEN cannot substitute for live #27 governance or qualifying independent non-author formal approval under #29.

Related: #3, #27, #29, #104, #105, #118, #120, #122

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Review details

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: f3fff002-6f2a-4668-9855-7a9f6e883dfc

📥 Commits

Reviewing files that changed from the base of the PR and between c85d710 and b93db04.

📒 Files selected for processing (2)

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

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