Speed up app-host test CI

[austinywang]

Fixes #6134

Summary

• cache app-host unit-test DerivedData on a stable per-shard path
• build the cmux app-host test bundle once per shard with build-for-testing
• run focused app-host gates and shard tests with test-without-building

Local validation

• ruby -e "require 'yaml'; YAML.load_file('.github/workflows/ci.yml'); puts 'ci.yml parsed'"
• git diff --check
• ./tests/test_ci_unit_test_spm_retry.sh
• ./tests/test_ci_self_hosted_guard.sh

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Summary by cubic

Speeds up app-host unit-test CI by caching per-shard DerivedData and reusing one build via test-without-building. Cuts duplicate builds and flakiness; fixes #6134.

• Refactors

  • Cache app-host unit-test DerivedData at a stable per-shard path via actions/cache, keyed on Xcode version, Ghostty revision, Package.resolved, and project; add broader restore fallbacks.
  • Build the app-host test bundle once per shard with xcodebuild build-for-testing; run focused gates and shard tests with test-without-building.
  • Move SwiftPM package resolution and the one-shot retry to the build step; drop the unreachable retry from the unit-test step; stop clearing DerivedData during test runs.
  • Regenerate Swift file length budget.

• Bug Fixes

  • Make the shell PATH-preservation test deterministic on CI by setting PATH inside the shell command to avoid zsh path_helper rewrites.

^{Written for commit 2bf31b9. Summary will update on new commits.}

Summary by CodeRabbit

• Bug Fixes
  • Improved reliability of macOS CI test runs by isolating build artifacts per shard and reusing smarter caches.
  • Added a safer build-and-retry flow when package dependencies can’t be resolved, reducing flaky failures.
  • Switched selected test runs to use prebuilt app-host tests for more consistent execution.

[vercel]

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Project	Deployment	Actions	Updated (UTC)
cmux	Ready	Preview, Comment	Jul 5, 2026 2:34am
cmux-staging	Building	Preview, Comment	Jul 5, 2026 2:34am

[coderabbitai]

📝 Walkthrough

Walkthrough

The app-host-unit-tests CI job gains a shard-specific DerivedData directory cached by Xcode version, Ghostty revision, and dependency manifests. A new "Build app-host tests" step runs xcodebuild build-for-testing with package resolution disabled and a one-shot retry on SwiftPM resolution failures. All subsequent test invocations—focused regressions and the main runner—switch to test-without-building, and the old inline retry block is removed.

Changes

App-host unit-test CI workflow

Layer / File(s)	Summary
Per-shard DerivedData cache setup .github/workflows/ci.yml	Creates a shard-specific DerivedData path under $RUNNER_TEMP and caches it keyed by .xcode-version, Ghostty revision, Package.resolved, and project.pbxproj, replacing run-id/attempt-based naming.
Build app-host tests with SwiftPM retry .github/workflows/ci.yml	Adds a build-for-testing step with -disableAutomaticPackageResolution and CMUX_SKIP_ZIG_BUILD=1; captures full build output and retries once after clearing ~/Library/Caches/org.swift.swiftpm and recreating DerivedData when "Could not resolve package dependencies" is detected.
Switch test runs to test-without-building and remove inline retry .github/workflows/ci.yml	Browser proxy mirror and Option/Alt regression steps, plus the main backgrounded unit-test runner, switch from test to test-without-building; the inline resolution retry block is removed and replaced with a comment pointing to the new build step.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• manaflow-ai/cmux#6464: Implements shard-specific DERIVED_DATA_PATH and the sharded xcodebuild invocation that this PR builds upon.
• manaflow-ai/cmux#6243: Previously added SwiftPM cache-clearing and retry logic in the unit-test step that this PR replaces with the new build step.
• manaflow-ai/cmux#6403: Adjusted the resolve verification/retry flow around .ci-source-packages, touching the same dependency self-healing path this PR restructures.

Suggested reviewers

• lawrencecchen

🐇 One build to rule them all, one cache to find it,
No more rebuilding — the DerivedData's primed!
test-without-building hops light on its feet,
The retry's tucked early, so failures are neat.
From 25 minutes to something much sweeter — 🥕

🚥 Pre-merge checks | ✅ 25

✅ Passed checks (25 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	The workflow changes address the main goals by caching DerivedData and building once before test-without-building runs.
Out of Scope Changes check	✅ Passed	The changes stay focused on the CI workflow and related test stability, with no clear unrelated scope added.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Cmux Swift Actor Isolation	✅ Passed	Only .github/workflows/ci.yml changed; no Swift sources or actor-isolation-sensitive declarations were introduced or worsened.
Cmux Swift Blocking Runtime	✅ Passed	Branch-only diff changes only .github/workflows/ci.yml; no Swift production files or blocking/timing sync primitives were introduced.
Cmux Browser Automation Off-Main	✅ Passed	PR only changes .github/workflows/ci.yml; no browser socket automation code or policy coverage is touched, so this rule isn’t implicated.
Cmux Expensive Synchronous Load	✅ Passed	Workflow-only PR: no production Swift files changed, so the expensive synchronous agent-load rule is not applicable.
Cmux Cache Substitution Correctness	✅ Passed	Only .github/workflows/ci.yml changed; no production Swift/TS/JS persistence/history/snapshot code was touched, so the cache-substitution rule is N/A.
Cmux No Hacky Sleeps	✅ Passed	PASS: The PR only changes .github/workflows/ci.yml, which the rule explicitly exempts; the diff removes a retry block and adds no new sleeps/waits.
Cmux Algorithmic Complexity	✅ Passed	Diff only touches .github/workflows/ci.yml, so no production Swift/TS/JS/shell/runtime algorithmic-complexity path changed.
Cmux Swift Concurrency	✅ Passed	The diff only changes .github/workflows/ci.yml; no Swift source files were modified, so it introduces no new legacy async patterns in cmux-owned Swift code.
Cmux Swift @Concurrent	✅ Passed	PR only changes .github/workflows/ci.yml; no Swift files or concurrency annotations are touched, so the Swift concurrent rule is not applicable.
Cmux Swift File And Package Boundaries	✅ Passed	The PR tip only edits .github/workflows/ci.yml; no production Swift files were changed, so the Swift boundary rule is not implicated.
Cmux Swiftpm Lockfiles	✅ Passed	Only .github/workflows/ci.yml changed; no cmux-owned .gitignore, Package.resolved, Package.swift, or xcodeproj package-reference files were touched.
Cmux Swift Logging	✅ Passed	PR changes are workflow-only; no Swift source files appear in the diff, so the Swift logging rule doesn’t apply.
Cmux User-Facing Error Privacy	✅ Passed	Only .github/workflows/ci.yml changed; its new strings are CI log/comments, not user-facing errors or sensitive output.
Cmux Full Internationalization	✅ Passed	Only .github/workflows/ci.yml changed; it’s CI operational config, and the i18n policy allows non-user-facing operational docs/tests. No locale assets changed.
Cmux Swiftui State Layout	✅ Passed	PR-only diff changes .github/workflows/ci.yml only; no SwiftUI sources or layout/state code are touched, so the SwiftUI state-layout rule is not applicable.
Cmux Architecture Rethink	✅ Passed	The PR only changes .github/workflows/ci.yml; it doesn’t alter Swift ownership/lifecycle architecture or introduce the banned patterns in Swift code.
Cmux Swift Auxiliary Window Close Shortcuts	✅ Passed	PR only changes .github/workflows/ci.yml; no Swift/UI window code or cmuxAuxiliaryWindowIdentifiers changes are present, so the rule isn’t triggered.
Cmux Source Artifacts	✅ Passed	Only changed path is .github/workflows/ci.yml, a CI config; no local output, caches, build artifacts, or scratch dirs were added to source control.
Cmux No Test Or Debug Seam In Production Source	✅ Passed	PR-specific diff vs the target branch only changes .github/workflows/ci.yml; no production Sources/** Swift files were modified, so no debug seam was introduced.
Cmux No Ambient Global State	✅ Passed	PR only changes .github/workflows/ci.yml; no production Swift code or ambient global-state additions are present.
Title check	✅ Passed	The title is concise and clearly summarizes the main change: speeding up app-host test CI.
Description check	✅ Passed	The description covers Summary, Testing, Review Trigger, and Checklist, with enough detail for this workflow change.

✨ 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 issue-6134-

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[greptile-apps]

Greptile Summary

This PR speeds up the app-host unit-test CI job by caching DerivedData at a stable per-shard path and splitting the workflow into a single build-for-testing step followed by test-without-building in all downstream test steps, eliminating redundant builds across the focused gates and shard tests.

• DerivedData caching: A stable path (cmux-deriveddata-app-host-unit-tests-shard-<N>) replaces the run-unique path, and actions/cache restores/saves with a full key (Xcode, Ghostty SHA, Package.resolved, project.pbxproj) plus three progressively broader restore-keys fallbacks for incremental cache hits.
• Build/test separation: A new "Build app-host tests" step runs build-for-testing once per shard (with the existing SPM retry logic moved here), and all three test steps (BrowserSystemProxyMirrorTests, GhosttyOptionAsAltModsTests, Run unit tests) switch from test to test-without-building, removing their own redundant builds and the now-unreachable SPM retry.
• Budget update: swift-file-length-budget.tsv is updated to reflect GhosttySurfaceView.swift shrinking from 4283 to 3964 lines.

Confidence Score: 5/5

Safe to merge — the changes are CI-infrastructure only, and the build/test separation logic is correct.

The workflow restructuring is well-reasoned: stable DerivedData paths enable caching, build-for-testing guarantees a complete bundle before any test-without-building step, and the SPM retry is correctly repositioned in the build step where it can actually recover. The three restore-key fallbacks address the previous-comment concern about full-key misses. No production Swift code is touched.

No files require special attention.

Important Files Changed

Filename	Overview
.github/workflows/ci.yml	Restructures the app-host CI job to cache DerivedData at a stable per-shard path, build the test bundle once with build-for-testing, and run all test steps with test-without-building; SPM retry is correctly moved to the build step; logic is sound.
.github/swift-file-length-budget.tsv	Updates GhosttySurfaceView.swift line-count budget from 4283 to 3964, reordering the table to keep it sorted; no issues.

Sequence Diagram

%%{init: {'theme': 'neutral'}}%%
sequenceDiagram
    participant Prep as Prepare DerivedData
    participant Cache as Cache DerivedData (restore)
    participant Resolve as Resolve Swift packages
    participant Build as Build app-host tests<br/>(build-for-testing)
    participant Gate1 as BrowserSystemProxyMirrorTests<br/>(test-without-building)
    participant Gate2 as GhosttyOptionAsAltModsTests<br/>(test-without-building)
    participant Tests as Run unit tests<br/>(test-without-building)
    participant CacheSave as Cache DerivedData (save)

    Prep->>Prep: rm -rf stable path, mkdir
    Cache-->>Prep: restore DerivedData (if cache hit)
    Resolve->>Resolve: xcodebuild -resolvePackageDependencies (up to 3 attempts)
    Build->>Build: xcodebuild build-for-testing
    alt SPM resolution failure
        Build->>Build: clear SwiftPM cache + DerivedData, retry once
    end
    Build-->>Gate1: pre-built .xctest bundle
    Build-->>Gate2: pre-built .xctest bundle
    Build-->>Tests: pre-built .xctest bundle
    Gate1->>Gate1: test-without-building (shard gate only)
    Gate2->>Gate2: test-without-building (shard gate only)
    Tests->>Tests: test-without-building (shard slice)
    Tests-->>CacheSave: completed DerivedData
    CacheSave-->>Cache: save (on cache miss + success)

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sequenceDiagram
    participant Prep as Prepare DerivedData
    participant Cache as Cache DerivedData (restore)
    participant Resolve as Resolve Swift packages
    participant Build as Build app-host tests<br/>(build-for-testing)
    participant Gate1 as BrowserSystemProxyMirrorTests<br/>(test-without-building)
    participant Gate2 as GhosttyOptionAsAltModsTests<br/>(test-without-building)
    participant Tests as Run unit tests<br/>(test-without-building)
    participant CacheSave as Cache DerivedData (save)

    Prep->>Prep: rm -rf stable path, mkdir
    Cache-->>Prep: restore DerivedData (if cache hit)
    Resolve->>Resolve: xcodebuild -resolvePackageDependencies (up to 3 attempts)
    Build->>Build: xcodebuild build-for-testing
    alt SPM resolution failure
        Build->>Build: clear SwiftPM cache + DerivedData, retry once
    end
    Build-->>Gate1: pre-built .xctest bundle
    Build-->>Gate2: pre-built .xctest bundle
    Build-->>Tests: pre-built .xctest bundle
    Gate1->>Gate1: test-without-building (shard gate only)
    Gate2->>Gate2: test-without-building (shard gate only)
    Tests->>Tests: test-without-building (shard slice)
    Tests-->>CacheSave: completed DerivedData
    CacheSave-->>Cache: save (on cache miss + success)

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_{Reviews (7): Last reviewed commit: "Regenerate Swift file length budget" | Re-trigger Greptile}