Add pnpm materialization profiles

[schickling-assistant]

Problem

The pnpm install helper had implicit dependency-materialization behavior. That made it hard for downstream repos to prove whether installs use job-local state, split shared files, or a future same-device hardlink profile.

Goal

Expose an explicit materialization profile contract and runtime evidence without switching the default Linux behavior to hardlink imports yet.

Decisions

• Add materializationProfile ? "auto" with explicit ciJobLocal, splitFilesCas, darwinSplitCas, linuxSharedHardlink, and isolated profiles.
• Keep Linux auto behavior-compatible via splitFilesCas; linuxSharedHardlink remains opt-in and fail-fast.
• Keep CI auto job-local, while preserving explicitly requested global profiles in CI.
• Add local-only overrides: localMaterializationProfile, localStoreDir, and localSharedFilesDir apply only outside CI.
• Add localOverridesRequireLinux so downstream repos can declare a Linux hardlink CAS boundary without leaking /var/lib Linux paths or hardlink policy into macOS.
• Validate same-device placement before explicit hardlink installs using Node filesystem stats.
• Include current dependency-materialization profile evidence in the install-state hash so contract/profile drift cannot silently hit the warm cache.
• Apply selected profile import policy to pnpm:update and pnpm:dedupe, not only pnpm:install.
• Record the registered profile trait in repair roots and refuse ambiguous legacy registry rows instead of replaying the caller's current profile for every sibling root.
• Convert notion-cli dependency FOD to Evergreen-managed per-system hash shape so full verification no longer blocks on an unrepairable literal slot.

Verification

• CI=1 bash nix/devenv-modules/tasks/shared/tests/pnpm.test.sh
  • Passed 38 helper tests.
• CI=1 bash nix/devenv-modules/tasks/shared/tests/pnpm-task-smoke.test.sh
  • Passed 30 smoke tests, including explicit hardlink evidence, hardlink import flags for update/dedupe, local-only CI fallback, and localOverridesRequireLinux with a simulated Darwin runtime.
• nixfmt --check nix/devenv-modules/tasks/shared/pnpm.nix
• git diff --check -- nix/devenv-modules/tasks/shared/pnpm.nix nix/devenv-modules/tasks/shared/tests/pnpm-task-smoke.test.sh
• Earlier FOD proof on this branch:
  • nix build .#notion-cli --no-link --print-build-logs on dev3 / x86_64-linux passed.
  • ssh dev4 ... nix build .#notion-cli --no-link --print-build-logs at commit a42a3e495 passed on aarch64-linux.
• devenv tasks run check:all --no-tui
  • FOD/genie/nix flake surfaces passed after the FOD repair.
  • Still failed in unrelated long integration surfaces: notion-datasource-sync e2e timeouts, one restate-effect endpoint readiness failure, and Vitest fork startup/teardown timeouts.

Complexity

Adds profile-selection helpers because downstream storage observability needs a stable contract and runtime evidence. The complexity is bounded to the pnpm task helpers and keeps hardlink materialization opt-in.

Concerns

• Linux auto still does not switch to hardlink; that remains gated on production CAS path provisioning, real-workload reuse/link-count evidence, install timing, and native rebuild safety.
• Darwin real-host proof is still pending. The smoke suite simulates non-Linux runtime gating, but we still need a clean macOS proof path.
• The downstream dotfiles live graph is currently blocked by /nix disk exhaustion on dev3; dotfiles #1219 records that as the current bottleneck.
• Evergreen can now reconcile the notion-cli hash slot, but its direct post-write evaluator still cannot import this package because build.nix requires src; real flake builds are the proof surface for this package.

Follow-ups

• Enable linuxSharedHardlink as the Linux default only after measured production proof.
• Add targeted real native-package rebuild coverage before hardlink default enablement.
• Add/repair a clean Darwin proof path that uses bulk temp space without pressuring the internal /nix volume.
• Continue downstream dotfiles Phase 9 rollout and reuse/amortization tracking.

References

• Related: schickling/dotfiles#1219

Posted on behalf of @schickling

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agent_name	🐧 co1-polar
agent_session_id	61111ff4-aff6-4a16-a4bf-ef47cef3e76a
agent_tool	Codex CLI
agent_tool_version	0.141.0
agent_runtime	Codex CLI 0.141.0
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runtime_profile	/nix/store/ynb6b5csz0wgbwqw1c43flnp450v5bjv-coding-agent-runtime-profile/share/coding-agents/profile.json
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worktree	dotfiles/schickling/2026-06-28-pnpm-overhead
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