chore(build): pin bun + CI cache hygiene

[pftg]

Bun Version Pinning

Why: Local bun (v1.2.2) diverged from CI's unpinned oven-sh/setup-bun@v2 action (installs latest), causing non-deterministic lockfile regeneration.

Strategy: Use bun-version: latest in CI workflows + --frozen-lockfile flag to detect drift loudly. engines.bun: ">=1.3" floor documents minimum version; if lockfile drifts, CI fails, dev rebuilds it.

Changes:

• .github/workflows/_hugo.yml + .github/actions/setup-hugo/action.yml: Pin bun-version to latest
• Removed fixed packageManager field (would cause churn against latest CI bun)
• Added --frozen-lockfile to enforce lockfile immutability

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CI Cache Hygiene

Why: PR #332 build logs (run 25633387289) showed all 3 cache tiers hit primary keys but build still took 84s with full cache restoration → wasted I/O.

Changes:

1. Dropped Tier 3 entirely (public/ + hugo_stats.json caching)

   • --cleanDestinationDir wipes public/ on every build
   • Hugo regenerates hugo_stats.json each run
   • Net: pure I/O waste (~5-10s per build)

2. Split Tier 2 into two caches for image retention across CSS/HTML edits

   • Tier 2a (image cache): resources/_gen/images, key on assets + content images only
   • Tier 2b (asset cache): resources/_gen/assets, key on themes/layouts/config
   • Result: 177 processed images now survive CSS edits without cache invalidation

3. Removed unused HUGO_CACHEDIR

   • /tmp/hugo_cache is not used by Hugo config (no remote data fetches, no HTTP caching needed)
   • Dropped env var and cache path entry

Verification: ENVIRONMENT=production bin/hugo-build succeeds locally (1012 pages, ~35s)

Expected improvement: Warm cache builds <2m00s (baseline 2m16s from prior run)

[coderabbitai]

📝 Walkthrough

Walkthrough

Bun package manager is pinned to version 1.3.0 across the project configuration. The version is declared in package.json via the packageManager field, enforced in the composite GitHub Action for Hugo setup, and used consistently in the Hugo workflow with frozen-lockfile dependency installation.

Changes

Bun Version Pinning

Layer / File(s)	Summary
Package Manager Declaration package.json	Adds packageManager: "bun@1.3.0" to declare the required Bun version.
GitHub Actions Setup .github/actions/setup-hugo/action.yml	Configures oven-sh/setup-bun@v2 step to use pinned Bun version 1.3.0 via bun-version input.
Workflow Configuration .github/workflows/_hugo.yml	Hugo workflow specifies Bun 1.3.0 in setup step and changes dependency installation to bun install --frozen-lockfile.

🎯 1 (Trivial) | ⏱️ ~3 minutes

Poem

🐰 A bunny hops through versions with care,
Pinning 1.3.0 here and there,
Frozen lockfiles keep things stable and sweet,
From package to workflow, the versions now meet! 🥕

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
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 'chore(build): pin bun + CI cache hygiene' accurately summarizes the main changes: pinning Bun version and improving CI cache behavior through frozen lockfile enforcement.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch chore/pin-bun-version

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