fix: Fix Metrics History Destruction & Self-Exclusion Blind Spot

[sahil-noon]

Meta

ID	Type	Confidence	Plan	Review
srmi	fix	3.5/5.0	10/10 tasks, 21/21 acceptance ✓	✓ 1 cycle

Pipeline: intake ✓ → apply ✓ → review ✓ → hydrate ✓ → ship → review-pr

Impact: +849/−5 code (excluding fab/, docs/) · +1234/−9 total

Summary

Claude Code purges session transcripts older than 30 days, so a machine's live ccusage view of old dates collapses toward zero — and tu's multi-machine sync treated that live fetch as authoritative, unconditionally overwriting correct per-day JSONL snapshots in the shared metrics repo ($5,160 measured destroyed; e.g. 2026-04-24 went $308.12 → $9.46). A compounding self-exclusion bug meant a machine could not see its own synced history once local transcripts were purged. This change makes day-files true high-water marks via a never-shrink guard in writeMetrics, ships a one-time repair script that restores shrunk files from the repo's git history (run manually post-release), and max-merges own-machine snapshots back into the live local view (fixing --by-machine and watch mode too).

Changes

• Never-shrink guard in writeMetrics (src/node/sync/sync.ts)
• One-time repair script (scripts/repair-metrics.mjs, new)
• Self-view max-merge (src/node/core/cli.ts + src/node/core/fetcher.ts)

[Copilot]

Pull request overview

This PR prevents multi-machine sync from silently destroying historical daily metrics after Claude Code transcript retention purges, and fixes a related “self-exclusion” blind spot where a machine could no longer see its own synced history once local transcripts were gone.

Changes:

• Added a never-shrink guard in writeMetrics so per-day snapshot files act as high-water marks and are not overwritten by lower totalCost values.
• Introduced a standalone one-time repair script (scripts/repair-metrics.mjs) to restore shrunk day-files from the metrics repo’s git history (dry-run by default, --write restores working tree only).
• Fixed own-machine self-view by max-merging local live entries with the machine’s own repo snapshots before summing with other machines.

Reviewed changes

Copilot reviewed 16 out of 16 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/node/sync/sync.ts	Adds the never-shrink write guard to protect historical day-file snapshots.
src/node/sync/tests/sync.test.ts	Adds coverage for shrink-skip, equal refresh, and corrupted/empty existing files.
scripts/repair-metrics.mjs	Adds a standalone repair tool to detect and restore shrunk metrics files from git history.
src/node/sync/tests/repair-metrics.test.ts	End-to-end tests for the repair script using a hermetic seeded git fixture repo.
src/node/core/fetcher.ts	Adds maxMergeEntries helper (whole-entry per-label max by totalCost).
src/node/core/cli.ts	Rewires merged fetch paths to max-merge own snapshots into the local view and read all machines in one pass.
src/node/core/tests/fetcher.test.ts	Adds unit tests for maxMergeEntries semantics (ties, copies, ordering, non-mutation).
src/node/core/tests/self-view-merge.test.ts	Composition test mirroring the multi-mode pipeline to validate corrected self-view behavior.
docs/memory/sync/multi-machine.md	Documents high-water-mark semantics, guarded writes, self-view max-merge, and the repair script contract.
docs/memory/sync/index.md	Updates sync memory index description/date to reflect new semantics.
docs/memory/cli/data-pipeline.md	Documents the updated multi-mode pipeline including maxMergeEntries.
docs/memory/cli/index.md	Updates CLI memory index date to reflect the pipeline update.
fab/changes/260610-srmi-fix-metrics-history-destruction/*	Adds/updates change tracking artifacts (intake/plan/status/history).

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