miner: capture bounded candidate context (labels/assignees/owner) in eligibility-exclusion fired-event metadata

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Problem

ORB's backtest system became able to replay logic changes (not just thresholds) only after #8129/#8130 captured bounded raw context in fired-event metadata — the exact inputs the rule evaluated. AMS's eligibility-exclusion capture has the same gap: recordEligibilityExclusionSignals (packages/loopover-miner/lib/discover-cli.ts) records ruleId/targetKey/outcome/occurredAt and no metadata, so a captured exclusion can never be re-evaluated under a candidate ContributionProfile — the inputs (labels, assignees, owner, the exact fields filterCandidatesByProfiles evaluates per FilterCandidate in contribution-profile-filter.ts) are dropped. This issue is the AMS mirror of ORB's bounded raw-context capture, and the hard prerequisite for the eligibility backtest CLI (separate issue).

Requirements

⚠️ Capture happens only in discover-cli.ts's existing capture helper. This issue is NOT satisfied by: changing filterCandidatesByProfiles' signature or return shape (contribution-profile-filter.ts is pure and stays untouched), capturing on the dry-run branch, or storing unbounded/whole-candidate objects.

• Widen recordEligibilityExclusionSignals' parameter type so each excluded entry's candidate carries optional labels?: string[], assignees?: string[], owner?: string — these fields are already present at runtime on the filter's excluded entries (the generic T passthrough of EligibilityExclusion<T>; see FilterCandidate); the call site passes them through with no new computation.
• Each recorded event gains metadata with exactly these bounds:
  • labels: at most 50 entries; assignees: at most 25 entries; each string truncated to 200 characters.
  • When a cap truncates (array length or string length), add truncated: true to the metadata; omit the key entirely when nothing was truncated.
  • Absent source fields are omitted from metadata (no nulls, no empty-array placeholders for missing data).
• Dry-run behavior unchanged: still no capture of any kind (the existing deliberate exclusion).
• Best-effort discipline unchanged: metadata capture must not introduce any new failure path that could abort discovery.
• Tests, all Codecov-visible (root-vitest mirror per the test(miner): mirror shouldReenter under root vitest for Codecov (#8347) #8479 precedent if needed):
  • Metadata recorded with all three fields when present; each field omitted when absent from the candidate.
  • Both arms of every cap: exactly-at-cap (no truncated key) and one-over-cap (clamped + truncated: true) for labels count, assignees count, and string length.
  • Dry-run records nothing (existing test extended or new).
  • 100% of changed lines and branches covered.

Deliverables

• Bounded metadata on eligibility-exclusion fired events per the exact caps above
• Pure filter module untouched; dry-run non-capture preserved
• Tests covering presence/omission and both arms of every cap, Codecov-visible

Links & Resources

• Epic: AMS parity for the ORB backtest/calibration system (blocked until ORB side is complete) #8107 (parent epic), calibration: capture bounded raw context (issueText/prTitle/prBody/diff) in linked_issue_scope_mismatch's fired-event metadata #8129/calibration: capture bounded raw context for the remaining isConfiguredGateBlocker codes, excluding secret_leak #8130 (the ORB bounded-capture precedent this mirrors), packages/loopover-miner/lib/discover-cli.ts (recordEligibilityExclusionSignals), packages/loopover-miner/lib/contribution-profile-filter.ts (FilterCandidate, EligibilityExclusion)

Boundaries

discover-cli.ts + tests only. No filter changes, no new events, no dry-run capture, no unbounded storage.

[linear-code]

JSO-5913