Proof chain active issues index

Hard truncation at 100 characters without ellipsis — proofSummary.ts:361 uses `substring(0, 100)` which can cut mid-word. Adding `+ '…'` when truncated would improve readability. Minor — the active issues index is a developer tool, not user-facing output.

File path segments lost in extractFileRefs — proofSummary.ts:253 regex uses `\b` word boundary which won't match after `/`. Callouts mentioning `src/utils/index.ts` will group under `index.ts`, potentially merging unrelated files from different directories. In practice, callout text from verify reports typically uses bare filenames (e.g., "Dead logic in projectKind.ts:105"), so this is dormant but worth knowing if callout format evolves.

ProofChain interface duplicated in three locations — work.ts:661, proof.ts:29, and now proofSummary.ts has `ProofChainEntryForIndex`. The gotcha explicitly warned about this. The builder chose a narrow projection interface rather than importing the full type — defensible, but the duplication count is growing. Consider consolidating in a future cycle.

A009 cap test doesn't verify WHICH callouts were dropped — proofSummary.test.ts:550-564 creates 25 identical-structure callouts and asserts count is 20, but doesn't verify the 5 dropped are the oldest. The separate "takes most recent callouts when capping at 20" test (line 691) does verify this. Together they provide full coverage, but A009 alone would pass even if the implementation kept the oldest instead of the newest.

A012 heading position test is fragile — proofSummary.test.ts:606 asserts `output.indexOf('# Active Issues') === 0`. If the function ever adds a leading newline or BOM, this breaks. The contract says "contains", but the test asserts position. Stricter than required — not wrong, but fragile.