fix!: include runid in cache key, restore freshest lockfile match

[poulet42]

as per @zkochan feedback here. This PR updates the cache system so:

• every run saves cache under a unique key, regardless if a cache entry already exists for the current lockfile
• cache restoration looks for the most recent lockfile match

Summary by CodeRabbit

• Bug Fixes

  • Improved cache restoration and saving to prevent failed or cancelled installations from being reused incorrectly.
  • Cache saves now use unique invocation keys, while restoration prioritizes the latest cache matching the current lockfile.
  • Repeated saves with an unchanged lockfile create separate entries, which may increase storage usage and evict older entries sooner.
  • Clarified cache-hit reporting to indicate an exact lockfile match rather than a fallback cache.

• Documentation

  • Updated guidance on cache keys, lockfile requirements, and storage considerations.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

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• src/cache-restore/keys.test.mjs
• src/cache-restore/keys.ts
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🔇 Additional comments (3)

src/cache-restore/keys.ts (1)

22-31: LGTM!

Also applies to: 33-35

src/cache-restore/keys.test.mjs (1)

3-3: LGTM!

Also applies to: 34-45, 105-119

src/cache-restore/run.ts (1)

10-10: LGTM!

Also applies to: 51-51, 65-76

---

📝 Walkthrough

Walkthrough

The cache flow now uses a lockfile-specific restore prefix and run-unique save keys. cache-hit checks lockfile matching. Cache saving no longer skips based on restored state. Documentation and tests cover the new behavior.

Changes

Cache key and restore flow

Layer / File(s)	Summary
Save key contract and tests src/cache-restore/keys.ts, src/cache-restore/keys.test.mjs	getPrimaryCacheKey is replaced by getSaveCacheKey. Save keys include the run ID and resolved runtime versions. Tests cover runtime, run, retry, restore-prefix, and exact-hit behavior.
Lockfile restore and cache-hit flow src/cache-restore/run.ts	Restore uses a lockfile-specific prefix with a plain-prefix fallback. Finalization creates a run-attempt-specific save key and reports whether the restored key matches the lockfile prefix.
Cache save behavior and documentation src/cache-save/run.ts, README.md, action.yml	Saving no longer skips work when restored state matches the primary key. Documentation describes run-unique save keys, fallback restoration, and lockfile-based cache-hit semantics.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Suggested reviewers: blankparticle, stanzilla

Sequence Diagram(s)

sequenceDiagram
  participant CacheRestore
  participant CacheService
  participant CacheFinalize
  CacheRestore->>CacheService: Restore with lockfile prefix and runtime-store fallback
  CacheService-->>CacheRestore: Return restored key
  CacheRestore->>CacheFinalize: Pass lockfile prefix and resolved runtimes
  CacheFinalize->>CacheService: Save with run ID and run attempt

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Merge Risk: 🔵 Low · up to 641dc

Each run now creates a restorable cache and later runs prefer the freshest matching lockfile cache. If a workflow fails after its cache key is finalized, a partial store could be restored by a later matching run; this is bounded but should remain an explicit owner follow-up.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 25.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 8 functions across 4 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes both primary changes: including the run ID in cache save keys and restoring the freshest matching lockfile cache entry.

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• Create a new PR

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_{A rabbit checks the lockfile bright
Each run saves with a key in sight
Partial stores cannot claim the way
Runtime paths remain distinct each day
The hit flag shows what matched today}

_{Comment @coderabbitai help to get the list of available commands.}

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[greptile-apps]

Confidence Score: 5/5

The PR appears safe to merge because the latest changes are comment-only cleanup and no outstanding correctness or security issue remains.

_{Reviews (5) · Last reviewed commit: "style(cache): remove redundant behavior ..."}

[coderabbitai]

Actionable comments posted: 1

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Inline comments:
In `@src/cache-restore/run.ts`:
- Line 71: Update the save-key construction in getSaveCacheKey to include
GITHUB_RUN_ATTEMPT alongside GITHUB_RUN_ID, ensuring each workflow attempt
produces a distinct immutable key. Add a regression test covering two attempts
with the same run ID and verifying different save keys.

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• src/cache-restore/keys.ts
• src/cache-restore/run.ts
• src/cache-save/run.ts

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[barclayadam]

One thing worth checking before this lands: the run id does not discriminate between jobs, so on a large fan-out this does not stop the reservation races — and it multiplies entries.

GITHUB_RUN_ID and GITHUB_RUN_ATTEMPT are properties of the workflow run, not the job. Every job in a matrix, and every job in a called reusable workflow, sees the same pair. So for a workflow whose jobs share a lockfile and runtime, getSaveCacheKey returns an identical string for all of them:

pnpm-cache-<os>-<arch>-<runtimes>-<lockfileHash>-<resolvedRuntimes>-<runId>-<runAttempt>

With the primaryKey === restoredKey skip removed, every one of those jobs now reaches saveCache unconditionally, all targeting that one key. One wins the reservation and the rest log:

##[warning]Failed to save: Unable to reserve cache with key …, another job may be creating this cache.

which is the same failure mode the current keying produces, just arrived at differently. On a fan-out of roughly a hundred jobs that is ~100 warnings per run, and ~99 full store uploads that are built and compressed before being discarded — in the region of 18s of job time each, against a store of several hundred MB.

The quota point you raised on #40 also gets sharper here. Today a given lockfile occupies one entry and is refreshed in place; with a run id it becomes one entry per run. A repository doing several deploys a day, with a store in the hundreds of MB, will hold many copies of near-identical content and push out entries that are still useful — including, in the worst case, the store the next run wanted to restore from.

Adding a per-job discriminator would fix the collision but makes the entry growth considerably worse, so that does not seem like the way out either.

The lever that would actually help this shape of workload is letting a job restore without saving — an input such as save: false (or cache: 'restore'). One warm upstream job publishes the store, the fan-out consumes it and skips the post step entirely. That removes the races by construction rather than by key uniqueness, and it reduces entries instead of adding them. Happy to open that as a separate feature request if it is useful — it is orthogonal to the partial-store problem this PR is solving, and would compose with it.