fix(review): parse a scalar source field written as a YAML sequence (#8016)

[real-venus]

Summary

source-evidence.ts and duplicates.ts each hand-roll a parseSimpleFrontmatter (a known parity-gap class between these two files — see #7250 / content-repo-spec.ts:132). duplicates.ts's parser has three branches — block-scalar, block/flow-sequence (inline === "", collects - item lines), and plain-scalar — but source-evidence.ts's had only two: the sequence branch was never ported.

Concretely: a scalar-only source field authored as a YAML sequence

documentationUrl:
  - https://docs.acme.example/guide

was captured by duplicates.ts (duplicate detection) but invisible to extractSubmittedSourceUrls/checkSubmittedSourceEvidence (the fetch-reachability hard-close gate) — the URL never got fetch-verified. documentationUrl is a scalar field, not one of the list fields (sourceUrls/retrievalSources) that listSourceUrlValues rescues, so nothing else caught it.

Fix

Port the missing block/flow-sequence branch verbatim from duplicates.ts (including its v8 ignore fallbacks for the ?? "" noUncheckedIndexedAccess guards). The existing block-scalar and plain-scalar cases are unchanged (the final else if (inline !== "") becomes a plain else, reached only for non-empty non-block inline values exactly as before).

Scope

• Narrow, single coherent change (one parser branch + its regression tests)
• In wantedPaths (src/review/content-lane/**, test/unit/**); no blockedPaths
• No secrets/private-scoring terms anywhere
• No generated-artifact changes required (internal parser; no API/schema/binding/migration change)

Validation

• npx vitest run test/unit/content-lane-source-evidence.test.ts — 86/86 pass (incl. 2 new #8016 tests: capture + fetch-verification)
• content-lane-duplicates suite still green (the source-of-truth parser is untouched)
• Honesty-checked: with the fix reverted, both new tests fail (documentationUrl sequence dropped) — they are genuine regressions, not tautologies
• typecheck clean on changed files (only the 2 pre-existing local semver TS7016s remain)
• git diff --check clean

Safety

• Behavior-preserving for block-scalar and plain-scalar inputs; the change only adds capture for a previously-dropped YAML shape
• Closes a gap that weakened the source-reachability gate — the fix strengthens it (more submitted URLs are fetch-verified, none newly bypass it)
• No auth/CORS surface touched; no secrets introduced

Closes #8016

[superagent-security]

Superagent didn't find any vulnerabilities or security issues in this PR.

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Tip

✅ LoopOver review result - approve/merge recommended

_{Review updated: 2026-07-22 14:06:56 UTC}

2 files · 1 AI reviewer · no blockers · readiness 98/100 · CI green · clean

✅ Suggested Action - Approve/Merge

• safe to merge

Review summary
This ports the missing block/flow-sequence frontmatter branch from duplicates.ts into source-evidence.ts's parseSimpleFrontmatter, so a scalar-only field (e.g. documentationUrl) authored as a YAML sequence is now captured and fetch-verified by the source-evidence gate, closing the parity gap described in #8016. The branch reorder (block-scalar → now empty-inline sequence → plain scalar else) is safe since isBlockScalarHeader("") is false, so the existing block-scalar path is unaffected, and list fields (retrievalSources etc.) are still handled separately by listSourceUrlValues so there's no double-parsing conflict. Two new regression tests (capture-level and full fetch-verification) exercise the real path and would fail without the fix per the PR's stated revert-check.

Nits — 2 non-blocking

• source-evidence.ts:165-179 duplicates three near-identical `/* v8 ignore next */` comments justifying unreachable `?? ""` fallbacks — consider factoring the bounded-index access into a small helper shared with the block-scalar loop to cut the repetition, though this mirrors duplicates.ts's existing style so it's a minor stylistic call.
• Nothing structurally to change; the port is verbatim per the PR description and the new tests target the exact previously-invisible path (documentationUrl as a sequence) rather than a fabricated scenario.

Decision drivers

• ✅ Code review — No blockers (1 reviewer)
• ✅ Gate result — Passing (No configured blocker found.)

Context & advisory signals — never blocks the verdict

Signal	Result	Evidence
Linked issue	✅ Linked	#8016
Related work	✅ No active overlap found	No same-issue or scoped active PR overlap found.
Change scope	✅ 20/20	Low review scope from cached public metadata (1 linked issue).
Validation posture	✅ 25/25	PR body includes validation/test evidence.
Contributor workload	✅ 10/10	Author activity: 106 registered-repo PR(s), 43 merged, 17 issue(s).
Contributor context	✅ Confirmed Gittensor contributor	real-venus; Gittensor profile; 106 PR(s), 17 issue(s).
Improvement	✅ Minor	risk: clean · value: minor · LLM: moderate

Linked issue satisfaction

Addressed
The diff ports the missing block/flow-sequence branch into source-evidence.ts's parseSimpleFrontmatter, mirroring duplicates.ts's logic, and keeps the plain-scalar/block-scalar branches intact by converting the trailing else-if into a plain else.

Review context

• Author: real-venus
• Role context: outside_contributor
• Public audience mode: oss maintainer
• Lane context: Repository is configured for direct PR review.
• Public profile languages: TypeScript, JavaScript, Python, Rust, CSS, MDX, Svelte, Swift
• Official Gittensor activity: 106 PR(s), 17 issue(s).
• PR-specific overlap: none found.

Contributor next steps

• Keep the PR focused and include validation evidence before maintainer review.

Signal definitions

• Related work = same linked issue, overlapping active PRs, or title/path similarity.
• Change scope = cached public metadata such as size labels, draft state, and review-burden hints.
• Validation posture = whether the PR provides enough public validation/test evidence for maintainer review.
• Contributor workload = public contributor activity and cleanup pressure, not a repo-wide quality failure.
• Contributor context = public GitHub/Gittensor identity context; non-Gittensor status is not a blocker.

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_{🟩 Safe / merged · 🟦 Advisory · 🟨 Held for review · 🟥 Blocked / closed}

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LoopOver approves — the gate is satisfied and CI is green.