fix(sdd-execute): install protobuf-compiler in host rust cleanup

[norrietaylor]

Root cause

• shared/sdd-rust-cleanup.md installs the Rust toolchain on the host runner but not protoc.
• The refresh step runs cargo clippy, which compiles the workspace + build scripts; prost/tonic crates shell out to protoc at build time.
• A manifest-adding task that pulls a protobuf crate fails the refresh: Could not find protoc (seen on a consumer pilot run adding a WireGuard mesh dep — the agent implemented the change but could not finalize the lock/lint cleanup, so the run produced no usable PR).

Fix

• New Install protobuf-compiler (host) step after the Rust toolchain install, gated on the same cargo_detect.changed. Best-effort: skips if protoc already present, installs via apt on Debian hosts, warns otherwise so clippy fails loudly on a genuinely missing tool.

Deploy

• Fragment edit only; recompile-locks regenerates the three sdd-execute-* locks on merge to main (ADR 0018). Retag v0.3.0 after the auto-recompile lands.

🤖 Generated with Claude Code

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 22791907-affe-4d61-b4e3-e2b9cf42e973

📥 Commits

Reviewing files that changed from the base of the PR and between d395045 and 2d22829.

📒 Files selected for processing (1)

• shared/sdd-rust-cleanup.md

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📝 Walkthrough

Summary by CodeRabbit

• Chores
  • Enhanced Rust project build reliability with automatic installation of required build dependencies when Rust code changes are detected.

Walkthrough

A new host post-step is added to shared/sdd-rust-cleanup.md that installs protobuf-compiler when the agent's patch touches Rust files (*.rs or Cargo.toml). The step checks for an existing protoc, falls back to apt-get install, and emits a warning if apt-get is unavailable.

Changes

Rust Cleanup: protoc Install Step

Layer / File(s)	Summary
Gated protoc install host post-step shared/sdd-rust-cleanup.md	Inserts a new "Install protobuf-compiler (host)" post-step gated on Rust-edit detection; checks for existing protoc, attempts apt-get install protobuf-compiler on Debian-like hosts, and logs a warning when apt-get is unavailable.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Possibly related PRs

• norrietaylor/spectacles#177: Modifies the same shared/sdd-rust-cleanup.md host-side Rust cleanup post-step logic for detecting Rust changes and running cargo fmt/clippy.
• norrietaylor/spectacles#178: Also modifies the shared host-side Rust cleanup logic in shared/sdd-rust-cleanup.md by adjusting the Rust post-step behavior in the same code-path area.
• norrietaylor/spectacles#160: Modifies the same Rust-edit–triggered host post-step logic, expanding it to run cargo fmt/cargo clippy --fix and conditional lock refresh.

Poem

🐰 Hop, hop, little build — no more protoc fright,
I check if it's there, then install it just right.
If apt-get is absent, I'll leave you a note,
A warning to heed so your clippy won't choke.
Best-effort, I say — a rabbit does try! 🦀

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and specifically describes the main change: installing protobuf-compiler in the host Rust cleanup step, which is the primary fix addressed in the pull request.
Description check	✅ Passed	The description is directly related to the changeset, explaining the root cause, the fix implemented, and deployment considerations that match the changes made to the markdown file.
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.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/execute-cleanup-protoc

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