fix(review): hash a JSON payload to prevent linked-issue-satisfaction cache-key collisions

[jeffrey701]

Problem

linkedIssueSatisfactionCacheInputFingerprint (src/review/linked-issue-satisfaction-cache-input.ts) builds the payload it hashes into a linked-issue-satisfaction cache key by "|"-joining free-form GitHub text fields (issueText, prTitle, prBody, diff):

const payload = [
  LINKED_ISSUE_SATISFACTION_CACHE_INPUT_VERSION,
  input.byok ? "1" : "0",
  input.provider ?? "", input.model ?? "",
  input.issueText ?? "", input.prTitle ?? "", input.prBody ?? "", input.diff ?? "",
].join("|");

None of that text is escaped, so a | occurring naturally inside one field can shift the field boundary and produce the same joined string for two genuinely different inputs — e.g. {issueText: "foo|bar", prTitle: "baz"} and {issueText: "foo", prTitle: "bar|baz"} (other fields equal) serialize identically and hash to the same fingerprint/cache key, so one PR's linked-issue-satisfaction verdict can be replayed for a different PR.

Its own comment says it "mirrors ai-slop-cache-input.ts's fingerprint discipline" — but that sibling actually builds its payload via JSON.stringify({...}), which structurally escapes delimiters and can't collide this way.

Fix

Build the payload as a JSON.stringify'd object, matching the sibling aiSlopCacheInputFingerprint. JSON escapes the field values ("foo|bar" vs "foo","bar|baz" serialize distinctly), so distinct inputs always produce distinct fingerprints. Field values are unchanged; only the serialization is structural now.

Test

test/unit/linked-issue-satisfaction-cache.test.ts adds a case asserting the two previously-colliding inputs (issueText: "foo|bar" / prTitle: "baz" vs issueText: "foo" / prTitle: "bar|baz") now yield different fingerprints. The existing BYOK-toggle and cache round-trip tests are unchanged and still pass.

Local: the fingerprint verification (distinct inputs differ; identical inputs stay deterministic) passes; tsc --noEmit clean on the changed file.

Closes #5939

[superagent-security]

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

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.16%. Comparing base (4749ff7) to head (8f32c51).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5976      +/-   ##
==========================================
- Coverage   95.16%   95.16%   -0.01%     
==========================================
  Files         589      589              
  Lines       46790    46789       -1     
  Branches    14943    14942       -1     
==========================================
- Hits        44528    44527       -1     
  Misses       1511     1511              
  Partials      751      751              

Flag	Coverage Δ
shard-1	43.50% <50.00%> (-0.42%)	⬇️
shard-2	36.36% <100.00%> (+0.15%)	⬆️
shard-3	31.98% <0.00%> (+<0.01%)	⬆️
shard-4	31.95% <0.00%> (+<0.01%)	⬆️
shard-5	32.26% <100.00%> (-0.24%)	⬇️
shard-6	44.89% <0.00%> (+0.18%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...rc/review/linked-issue-satisfaction-cache-input.ts	100.00% <100.00%> (ø)

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✅ LoopOver review result - approve/merge recommended

_{Review updated: 2026-07-15 05:27:27 UTC}

2 files · 1 AI reviewer · no blockers · readiness 82/100 · CI green · clean

✅ Suggested Action - Approve/Merge

• safe to merge

Review summary
This replaces the delimiter-vulnerable `"|"`-join in `linkedIssueSatisfactionCacheInputFingerprint` with `JSON.stringify`, matching the sibling `aiSlopCacheInputFingerprint` pattern the code already claimed to mirror. Field values are unchanged, only the serialization changed, and since object literal key order is deterministic across calls, the JSON string is stable for identical inputs. The added test directly reproduces the described collision (`issueText: "foo|bar"` + `prTitle: "baz"` vs `issueText: "foo"` + `prTitle: "bar|baz"`) and asserts distinct fingerprints, which is the right regression test for this exact bug class.

Nits — 3 non-blocking

• src/review/linked-issue-satisfaction-cache-input.ts: since LINKED_ISSUE_SATISFACTION_CACHE_INPUT_VERSION isn't bumped, every existing cached fingerprint for identical inputs will now mismatch (old '|'-joined payload vs new JSON payload) and silently miss the cache once — worth a one-line note in the PR description so operators aren't surprised by a cache-cold blip after deploy.
• PR description says 'Closes fix(mcp): keep repo root out of API payloads #59' but the test comment cites '(fix(review): linkedIssueSatisfactionCacheInputFingerprint's delimiter-joined payload allows cache-key collisions across different prompts #5939)' — worth reconciling which issue number is authoritative before merge.
• Consider bumping LINKED_ISSUE_SATISFACTION_CACHE_INPUT_VERSION alongside this change so the version-prefixed cache key makes the payload-format change explicit rather than relying on the hash naturally differing.

Signal	Result	Evidence
Code review	✅ No blockers	1 reviewer
Linked issue	✅ Linked	#5939
Related work	⚠️ 2 scoped overlaps	Top overlaps are listed below; lower-confidence bulk is hidden.
Change scope	❌ 8/20	High 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: 131 registered-repo PR(s), 63 merged, 33 issue(s).
Contributor context	✅ Confirmed Gittensor contributor	jeffrey701; Gittensor profile; 131 PR(s), 33 issue(s).
Gate result	✅ Passing	No configured blocker found.
Improvement	✅ Minor	risk: clean · value: minor · LLM: moderate

Linked issue satisfaction

Partially addressed
The PR correctly switches to a JSON.stringify-based structured payload and adds a regression test proving the previously-colliding '|' inputs now yield distinct fingerprints, satisfying the core collision fix. However, the diff shows no change to LINKED_ISSUE_SATISFACTION_CACHE_INPUT_VERSION, which the issue explicitly requires bumping so existing cache rows keyed under the old collision-prone for

Review context

• Author: jeffrey701
• Role context: outside_contributor
• Public audience mode: oss maintainer
• Lane context: Repository is configured for direct PR review.
• Public profile languages: not available
• Official Gittensor activity: 131 PR(s), 33 issue(s).
• Related work: Items reference the same linked issue fix(review): linkedIssueSatisfactionCacheInputFingerprint's delimiter-joined payload allows cache-key collisions across different prompts #5939. (issue #5939)
• Related work: Open PR work references issue fix(review): linkedIssueSatisfactionCacheInputFingerprint's delimiter-joined payload allows cache-key collisions across different prompts #5939. (issue #5939)

Contributor next steps

• Start here: Review top overlaps.
• Then work through the remaining 2 steps in the Signals table above.

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.