fix(scoring): inject server-side time decay into score breakdown paths

[JSONbored]

Motivation

• The new score-breakdown HTTP route and MCP tool built previews using caller-supplied input and omitted the server-gated applyTimeDecay injection, causing aged PRs to be reported without the time-decay multiplier and returning inflated effectiveEstimatedScore values.
• The intent is to preserve the server-side owner-gated behavior (SCORING_TIME_DECAY_ENABLED) used by existing preview endpoints so breakdowns remain accurate and consistent.

Description

• Inject applyTimeDecay: isTimeDecayEnabled(c.env) before calling buildScorePreview in the /v1/scoring/explain-breakdown route (src/api/routes.ts).
• Inject applyTimeDecay: isTimeDecayEnabled(this.env) before calling buildScorePreview in the MCP explainScoreBreakdown tool (src/mcp/server.ts).
• Add integration coverage to test/integration/api.test.ts that enables SCORING_TIME_DECAY_ENABLED, sends an aged PR input (prAgeHours), and asserts the breakdown's effectiveEstimatedScore matches the preview's decayed estimate, including minimal type assertions to satisfy TypeScript.

Testing

• Ran type checking with npm run typecheck and it succeeded.
• Ran the focused integration test with npx vitest run test/integration/api.test.ts -t "serves deterministic signal endpoints" --reporter=verbose and the test passed (1 passed, 36 skipped).
• Performed git diff --check as part of the workflow and there were no whitespace/format issues.

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Codex Task

[ghost]

Note

Gittensory Gate skipped

PR closed before full evaluation. No late first comment was created.

Signal	Result	Evidence	Action
Gate result	⚠️ Skipped	#881 is no longer open.	No action.

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[superagent-security]

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

[ghost]

gittensory · advisory review

Reviewed 3 changed file(s) — two independent AI reviewers.

Changed files: src/api/routes.ts, src/mcp/server.ts, test/integration/api.test.ts

Suggested action: 🛠️ Request changes. (reviewers split: request changes / merge) Address the suggestions below before merging.

Reviewer A · gpt-oss-120b — recommends 🛠️ request changes
The PR adds server‑side injection of the time‑decay flag into scoring previews and breakdowns, and updates tests to verify the behavior when the feature is enabled.

Suggestions

• Add an import for isTimeDecayEnabled in both src/api/routes.ts and src/mcp/server.ts (e.g., import { isTimeDecayEnabled } from '../scoring/model';).
• Consider adding a test case where SCORING_TIME_DECAY_ENABLED is unset or false to confirm the flag is not applied.
• Verify that the buildScorePreview signature accepts the extended input shape (applyTimeDecay?: boolean). If not, update the type definition accordingly.

Worth double-checking

• Missing import will cause a TypeScript compilation error, breaking the build.
• If buildScorePreview does not expect the new field, runtime errors could occur.
• The test assumes the API response includes timeDecayMultiplier; a mismatch would cause false failures.

Reviewer B · mistral-small-3.1-24b-instruct — recommends ✅ merge
This PR injects server-side time decay into the score breakdown paths, ensuring that time decay is applied based on an owner-gated global setting. The changes are well-documented and include necessary tests.

Suggestions

• Consider adding a comment explaining why the applyTimeDecay field is being added to the input object in both src/api/routes.ts and src/mcp/server.ts.
• Ensure that the isTimeDecayEnabled function is thoroughly tested, especially edge cases where the environment variable might be unset or have unexpected values.

Worth double-checking

• Verify that the time decay logic does not introduce any regressions in the scoring model.
• Check that the new tests cover all possible scenarios, including cases where time decay is disabled.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.71%. Comparing base (5d9d73a) to head (b237381).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #881   +/-   ##
=======================================
  Coverage   96.71%   96.71%           
=======================================
  Files         108      108           
  Lines       14641    14643    +2     
  Branches     5298     5298           
=======================================
+ Hits        14160    14162    +2     
  Misses        102      102           
  Partials      379      379           

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