ci: report the correct pnpmDeps hash when flake.nix is stale

[clay-good]

Status: ready for review.

What was wrong: every root lockfile change invalidates the pnpmDeps FOD hash pinned in flake.nix, and Dependabot cannot regenerate it — so Nix Flake Validation fails on every npm bump PR (#1810, #1811, and #1427 before them). The job already had everything needed to report the right value: it runs scripts/update-flake.sh, which computes the hash from pnpm-lock.yaml. But that step ran after nix build, so on a stale hash the build failed first and the script never ran. What the log showed instead was pnpm's:

ERR_PNPM_NO_OFFLINE_TARBALL  A package is missing from the store but cannot
download it in offline mode. The missing package may be downloaded from
https://registry.npmjs.org/zod/-/zod-4.5.4.tgz

That names a tarball, not a hash. Worse, the standard recovery — set hash = "", push, read the got: line — costs a second full CI run, because a stale hash produces no mismatch at all (the fetch succeeds against the old store and fails later, offline). Landing #1814 took exactly that two-round dance.

How it was fixed: run scripts/update-flake.sh first, then compare. If it rewrote flake.nix, the hash was stale: the job prints the diff and fails with a GitHub error annotation naming the value to paste. flake.nix is then restored and nix build runs against the committed file, so everything downstream is unchanged. The two now-redundant trailing steps (Validate update script, Check flake.nix modifications) are removed — the script runs earlier, and its result is asserted rather than just echoed.

Replication / proof: pushed a deliberately stale hash to this branch and let CI run (job log):

✓ Calculated hash: sha256-SNPeEUa+amkZYRO5tHeUwDBT4betXYPKnfZiEyhN7fE=
-              hash = "sha256-0000000000000000000000000000000000000000000=";
+              hash = "sha256-SNPeEUa+amkZYRO5tHeUwDBT4betXYPKnfZiEyhN7fE=";
Error: Stale pnpmDeps hash. Set pnpmDeps.hash to sha256-SNPeEUa+... and push.

34 seconds, one run, correct value — against a whole extra CI cycle before. That commit is removed from the branch; CI here is green on the real hash, which exercises the pass path.

Notes / nits: this deliberately does not make the check advisory on PRs, which is what I first suggested when handing over #1814. It would be the wrong trade: a merged stale hash breaks nix build for flake users on main until someone notices, and lockfile changes land roughly weekly, so main's flake would be broken more often than not. It also contradicts openspec/specs/ci-nix-validation/spec.md, which requires the job for merge. Making the gate cheap to satisfy beats moving the breakage downstream. If unattended Dependabot merges are still the goal, the honest version is auto-repair on main (a bot PR that pushes the hash after merge) — a bigger change, and a maintainer call.

🤖 Generated with Claude Code

Summary by CodeRabbit

• Chores
  • Improved automated build validation by detecting and reporting stale dependency metadata before builds run.
  • Ensured validation restores configuration files after checks, regardless of the outcome.
  • Streamlined workflow checks by removing separate post-build update-script validation and modification checks.

[coderabbitai]

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📝 Walkthrough

Walkthrough

The Nix validation job checks pnpmDeps hashes before nix build, reports stale hashes with a block-scoped extraction, restores flake.nix, and removes the later duplicate check.

Changes

Nix validation

Layer / File(s)	Summary
Pre-build pnpmDeps hash verification .github/workflows/ci.yml	The job runs scripts/update-flake.sh before nix build, detects changes to flake.nix, reports the hash from the pnpmDeps block, fails for stale hashes, and restores the file. The later update and modification check was removed.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: ⚪ Minimal · up to 2fa12

The CI update validates stale pnpm dependency hashes before building and restores the flake afterward. No concrete merge-blocking risk remains in the available evidence.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the primary change: CI now reports the correct pnpmDeps hash when flake.nix is stale.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0…
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.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch ci/report-stale-flake-hash

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Actionable comments posted: 1

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Inline comments:
In @.github/workflows/ci.yml:
- Line 197: Update the hash extraction in the CI workflow and the corresponding
lookup and replacement logic in scripts/update-flake.sh to operate only within
the pnpmDeps block, so they target pnpmDeps.hash rather than the first matching
hash assignment.

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[clay-good]

Applied the scoping fix in 2fa1251: the reported value now comes from within the pnpmDeps block rather than the first hash in the file.

Not changed, and worth a separate look: scripts/update-flake.sh has the same first-match assumption in its replacement step (sed "s|hash = \"sha256-[^\"]*\"|...|" is unanchored, so it would rewrite every hash = "sha256-…" line in flake.nix, not just pnpmDeps'). Today there is exactly one such line so nothing is wrong, but if a second FOD is added the script would overwrite it with pnpm's hash. I left it alone because I can't run Nix locally to test a change to the rewrite path — flagging it rather than fixing it blind.

[clay-good]

Reviewed the reordering; it holds up, plus one merge-order note.

The core insight is right and worth stating plainly: run update-flake.sh before nix build and a stale hash is reported as the exact value to paste; run it after and the same staleness has already surfaced as ERR_PNPM_NO_OFFLINE_TARBALL, which names a missing tarball and never the hash. The old steps only ran the script once the build had already succeeded, so they could never report the failure they existed to catch.

Checks I made:

• Step ordering is safe. Restore flake.nix carries if: always() and sits between the verify step and nix build, so the build always runs against the committed flake.nix whether verification passed or failed, and a failed verify still restores before the job stops.
• The sed scoping is not paranoia. sed -n '/pnpmDeps = /,/};/p' before extracting the hash means a second fixed-output derivation added above pnpmDeps cannot make the error message report the wrong hash. A bare first-match would.
• lib is in scope for the surrounding file (inherit (pkgs) lib at flake.nix:25), unchanged here.
• No Nix in this sandbox, so I could not execute the job; Nix Flake Validation passing on CI at this head is the real signal.

Merge-order note. This conflicts with #1785, which adds a completion-artifact guard to the same nix job in .github/workflows/ci.yml (and adds src/commands/completion.ts plus src/core/completions/** to the Detect changes filter, since the Nix build shells out to the completion generator). The two edits are in the same job but different steps, so the resolution is a union rather than a choice.

Landing this one first would help the rest of the batch: #1814 moves the root lockfile and therefore the pnpmDeps hash, and this is what makes that class of failure legible.