Handle non-finite issue similarity in the canonical deduplication formatter

[stranske]

Why

Canonical source repair for the accepted user-filed delivery issue stranske/Ready#561. At main 9a16cbf, scripts/langchain/issue_dedup.py:219 clamps and rounds scores without validating finiteness. Reproduction confirms NaN raises ValueError and positive infinity misleadingly renders 100%. The script is copy-delivered to Ready by .github/sync-manifest.yml:618; Ready AGENTS.md requires the correction to land in Workflows first.

Scope

Implement Ready #561's existing non-finite similarity contract in its canonical Workflows source and focused test suite. This issue routes already accepted work to the owning repository. Ready #561 stays open for downstream sync and consumer acceptance.

Non-Goals

• Do not change FAISS construction, score selection, similarity thresholds or finite-score semantics.
• Do not edit consumer copies directly or manage generated sync PRs in this implementation.
• Scaffold-only completion does NOT count: catching ValueError without a math.isfinite guard and meaningful regression tests does not deliver this issue.

Tasks

• Guard _format_similarity in scripts/langchain/issue_dedup.py with math.isfinite and return 0% for NaN and either infinity.
• Extend tests/scripts/test_issue_dedup.py with non-finite helper and comment rendering cases and finite clamping and rounding regressions.
• Verify the existing copy delivery entry for scripts/langchain/issue_dedup.py in .github/sync-manifest.yml and record Ready [Follow-up] Unmet criteria from PR #560 #561's remaining consumer sync in the PR.

Acceptance Criteria

• python3 -m pytest tests/scripts/test_issue_dedup.py tests/scripts/test_issue_dedup_smoke.py -q -o addopts='' exits 0; tests prove NaN and both infinities render 0%, public comments retain issue links, and finite scores preserve clamping and rounding. Capture command and results in the PR body.
• python3 -c "from scripts.langchain.issue_dedup import _format_similarity; assert _format_similarity(float('nan')) == '0%'" exits 0; capture result in the PR body.
• Deliberate-break gate: remove the math.isfinite guard in scripts/langchain/issue_dedup.py, run python3 -m pytest tests/scripts/test_issue_dedup.py -k nonfinite -q -o addopts='' and confirm NaN and infinity failures; restore exact source and rerun the full focused suite successfully. Capture both outcomes in the PR body.

Implementation Notes

The existing manifest delivery is copy, directly from the canonical script; no duplicate template or new mapping is needed. Existing focused suite is tests/scripts/test_issue_dedup.py rather than the consumer tests/test_main.py. Before fix with new regression cases: 2 failed (NaN and positive infinity), 12 passed. Delivery owner for the consumer sync is Maint 71 after the source PR merges; Ready #561 remains open until its named consumer gate passes.

[agents-workflows-bot]

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