ci: make release sccache failures non-fatal

[i386]

Summary

• put a job-local disk cache in front of the GitHub Actions sccache backend
• treat cache write and server I/O failures as non-fatal compiler fallbacks
• preserve the existing disk-only startup fallback and enforce the contract in xtask
• synchronize the CI topology documentation and inventory

Investigation

Release run https://github.com/Mesh-LLM/mesh-llm/actions/runs/30063516285 failed for two cache-related reasons:

• four Linux GPU jobs received an Actions cache service-unavailable HTML response while sccache was starting during compiler probing
• the Windows ROCm native-runtime job aborted when sccache could not persist a temporary cache file

Both failures blocked release artifacts even though the compiler inputs and build logic were otherwise valid.

Validation

• actionlint -config-file .github/actionlint.yaml
• git diff --check
• just check-release
• just with-lld cargo test -p xtask workflow_checks
• just with-lld cargo fmt --all -- --check
• just with-lld cargo check -p xtask
• just with-lld cargo clippy -p xtask --all-targets -- -D warnings

A release workflow dispatch was not started: the repository CI policy requires explicit authorization for that expensive live operation.

Summary by CodeRabbit

• CI Improvements

  • Improved build-cache reliability with a disk-first cache and best-effort remote caching.
  • Cache connection and write failures now degrade gracefully without interrupting builds.
  • Builds fall back to local compiler execution when the remote cache service is unavailable.

• Documentation

  • Updated CI and runner guidance to clarify cache behavior, fallback handling, and configuration requirements.

[coderabbitai]

📝 Walkthrough

Walkthrough

The PR configures sccache with a disk-first, best-effort GitHub Actions cache chain, adds disk-only fallback behavior, strengthens release contract validation, and updates CI documentation and inventory.

Changes

sccache cache contract

Layer / File(s)	Summary
Runtime cache configuration .github/actions/configure-sccache-gha/action.yml, .github/workflows/release.yml	Configures disk and GitHub Actions caching, ignored server I/O and write errors, and disk-only fallback when remote caching is unavailable.
Release contract validation tools/xtask/src/workflow_checks.rs	Validates required sccache settings and adds failures for missing write fallback or disk-first cache-chain configuration.
Documentation alignment .agents/skills/manage-ci/references/current-inventory.md, ci/ci.md	Documents cache tiers, failure handling, local fallback, remote probe behavior, and the baked-binary requirement.

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

Sequence Diagram(s)

sequenceDiagram
  participant ReleaseWorkflow
  participant ConfigureSccacheGHA
  participant Sccache
  participant GithubActionsCache
  ReleaseWorkflow->>ConfigureSccacheGHA: configure sccache environment
  ConfigureSccacheGHA->>Sccache: start disk,gha cache chain
  Sccache->>GithubActionsCache: probe best-effort remote cache
  ConfigureSccacheGHA->>Sccache: restart with disk-only chain on probe failure

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Possibly related PRs

• Mesh-LLM/mesh-llm#1059: Updates the related CI contract documentation and inventory.
• Mesh-LLM/mesh-llm#1067: Updates the same action and release container contract validation.

Suggested reviewers: ndizazzo, michaelneale

🚥 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 matches the main change: release CI now treats sccache/GHA cache failures as non-fatal.
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.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[coderabbitai]

🧹 Nitpick comments (1)

tools/xtask/src/workflow_checks.rs (1)

439-459: 🎯 Functional Correctness | 🔵 Trivial | ⚡ Quick win

Validate exact configuration values, not substrings.

ensure_contains can accept malformed workflow values such as SCCACHE_MULTILEVEL_CHAIN: disk,gha-disabled or SCCACHE_MULTILEVEL_WRITE_ERROR_POLICY: ignore-disabled. Since this checker gates the release fallback contract, use exact-line/scoped validation (or parsed YAML/source checks) and add wrong-value regression tests.

Also applies to: 487-502

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@tools/xtask/src/workflow_checks.rs` around lines 439 - 459, The release
workflow checks in the validation function around the required sccache entries
currently allow malformed values through substring matching. Replace the
ensure_contains checks for SCCACHE_DIR, SCCACHE_IGNORE_SERVER_IO_ERROR,
SCCACHE_MULTILEVEL_CHAIN, and SCCACHE_MULTILEVEL_WRITE_ERROR_POLICY with
exact-line or scoped YAML/source validation, and add regression tests proving
suffixed or otherwise incorrect values are rejected.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Nitpick comments:
In `@tools/xtask/src/workflow_checks.rs`:
- Around line 439-459: The release workflow checks in the validation function
around the required sccache entries currently allow malformed values through
substring matching. Replace the ensure_contains checks for SCCACHE_DIR,
SCCACHE_IGNORE_SERVER_IO_ERROR, SCCACHE_MULTILEVEL_CHAIN, and
SCCACHE_MULTILEVEL_WRITE_ERROR_POLICY with exact-line or scoped YAML/source
validation, and add regression tests proving suffixed or otherwise incorrect
values are rejected.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: d847d9fd-0b85-4259-a9c1-ecf19b86d64a

📥 Commits

Reviewing files that changed from the base of the PR and between cdd793b and ae34f48.

📒 Files selected for processing (5)

• .agents/skills/manage-ci/references/current-inventory.md
• .github/actions/configure-sccache-gha/action.yml
• .github/workflows/release.yml
• ci/ci.md
• tools/xtask/src/workflow_checks.rs