feat(B-0557 slice 2): try/catch readFileSync + readdirSync in audit tool

[AceHack]

Summary

• Addresses Copilot P1 finding from PR feat(B-0553): audit-backlog-status-drift tool + 16 tests (incl. 2nd FP class) #3758: enumerateOpenRows() could throw and abort the whole audit on a single unreadable backlog file (permission denied, transient FS error, etc.).
• Fix: wrap both readdirSync and readFileSync in try/catch; warn to stderr; continue with remaining files.
• Bundles peer Otto-Desktop's tick shard 10fb6e5 (brief-ack extreme cost-aware tier substrate).

Test plan

• bun test tools/hygiene/audit-backlog-status-drift.test.ts → 16 pass / 0 fail / 28 expect calls (no regression)
• bun tools/hygiene/audit-backlog-status-drift.ts --json still produces 33+ candidates from main
• Stderr warnings clearly name the failed file(s) when triggered

Composes with

• B-0557 — parent row (2 of 4 slices now in flight, plus PR feat(B-0557 slice 1): add --check flag to audit-backlog-status-drift #3783 for slice 1)

🤖 Generated with Claude Code

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[Copilot]

Pull request overview

Improves the resilience of the audit-backlog-status-drift hygiene tool by preventing filesystem read errors from aborting the entire audit run, and adds a new hygiene-history tick shard documenting related operational context.

Changes:

• Wraps readdirSync and readFileSync in try/catch inside enumerateOpenRows() to warn-and-continue on unreadable directories/files.
• Emits stderr warnings with the directory/file path and error message when reads fail.
• Adds a new docs/hygiene-history/ticks/... shard documenting the session tick.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
tools/hygiene/audit-backlog-status-drift.ts	Adds defensive error handling around directory and file reads to avoid aborting audits on a single unreadable entry.
docs/hygiene-history/ticks/2026/05/16/0644Z.md	Adds a new tick shard entry documenting the session state and related PR context.

Comments suppressed due to low confidence (1)

tools/hygiene/audit-backlog-status-drift.ts:212

• Same issue as above: casting err as Error risks losing information for non-Error throws. Use err instanceof Error ? err.message : String(err) for consistent, safe stderr output.

                process.stderr.write(
                    `audit-backlog-status-drift: unable to read ${path}: ${(err as Error).message}\n`,
                );

[AceHack]

Lior Antigravity Check: Clean slice, good error boundaries. No blob detected.

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.