ci: reuse the headless cmux-tui build in SDK conformance

[teamleaderleo]

Problem

seven-language live conformance in cmux-tui-sdks.yml takes about 7 minutes. About 5 of those go to "Build exact headless cmux-tui", which compiles cmux-tui from scratch every time. On the revert in #14106 the build started at 02:19:39 and finished at 02:24:35. The tests themselves took 66 s.

That run changed nothing under cmux-tui/. It started only because the workflow's push path filter lists about 25 workflow files, and #14101 and its revert each edited one comment line in cmux-tui-artifacts.yml.

Resulting behavior

The job keys the built binary on exactly what the build reads:

• the git tree of cmux-tui/
• the ghostty submodule commit
• zig 0.16.0 and the runner OS and arch

The Rust toolchain is pinned inside the tree by rust-toolchain.toml. When the key hits, the compile is skipped and the job goes straight to the conformance run. Pull requests only restore. Pushes to main save, which matches tests/test_ci_pull_request_caches_are_read_only.py.

Keying on the tree hash is conservative: an edit anywhere under cmux-tui/, bindings included, misses and compiles as it does today.

Testing

• actionlint is clean on cmux-tui-sdks.yml.
• tests/test_tui_publish_workflow_security.py and tests/test_ci_pull_request_caches_are_read_only.py pass.
• Not yet verified: the first push to main after this lands should save the cache, and the next unchanged-tree run should skip the build. I'll post both run links here.

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Summary by cubic

Caches the headless cmux-tui build in the SDK conformance job so unchanged trees skip the ~5-minute compile.

• The key is the cmux-tui/ tree hash plus the ghostty submodule commit, the pinned zig and Rust toolchains, and the runner OS and arch; any edit under cmux-tui/ misses and compiles as today.
• Pull requests only restore; pushes to main save, so the first push after this lands populates the cache.

^{Written for commit 3a382ca. Summary will update on new commits.}

Summary by CodeRabbit

• Chores
  • Improved the efficiency of automated conformance checks by reusing cached builds. This may reduce build time without changing the app’s features or behavior.

[github-actions]

All contributors have signed the CLA ✍️ ✅
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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository: manaflow-ai/cmux/.coderabbit.yaml

Review profile: ASSERTIVE

Plan: Advanced

Run ID: bd67eb81-ae84-4ae0-8d29-0e9c8be79893

📥 Commits

Reviewing files that changed from the base of the PR and between 83641ea and 3a382ca.

📒 Files selected for processing (1)

• .github/workflows/cmux-tui-sdks.yml

Included review availability: Your plan provides up to 10 included reviews per hour; 0 remain after this review.

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📝 Walkthrough

Walkthrough

The conformance job now caches the compiled headless cmux-tui binary. It keys the cache by runner OS and architecture, Zig version, and the cmux-tui and ghostty git hashes. It saves cache entries only on push events.

Changes

Headless Build Cache

Layer / File(s)	Summary
Restore, build, and save the binary .github/workflows/cmux-tui-sdks.yml	The workflow restores the binary using the computed cache key. It skips the build on a cache hit and saves the build on push events when the cache misses. Pull-request events do not save cache entries.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~8 minutes

Change: Refactor

Merge Risk: ⚪ Minimal · up to 3a382

The cache can reuse the binary across commits without affecting the conformance behavior checked by this job. No merge-blocking issue remains.

🚥 Pre-merge checks | ✅ 25

✅ Passed checks (25 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main change: reusing the headless cmux-tui build in SDK conformance CI.
Description check	✅ Passed	The description explains the problem, resulting behavior, cache key, restore/save policy, and testing status. It covers the required summary and testing content. The demo video is not applicable to th…
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0…
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.
Cmux Cloud Persistent Session And Early Input	✅ Passed	PASS: The pull request changes only .github/workflows/cmux-tui-sdks.yml. It adds cache key, restore, conditional build, and save steps for the headless cmux-tui binary. It does not change Cloud te…
Cmux Swift Actor Isolation	✅ Passed	The pull request changes only .github/workflows/cmux-tui-sdks.yml. The diff adds GitHub Actions cache key, restore, build condition, and save steps. It contains no Swift files or Swift production co…
Cmux Swift Blocking Runtime	✅ Passed	The pull request changes only .github/workflows/cmux-tui-sdks.yml. It adds GitHub Actions cache restore/save steps and a conditional build. It contains no Swift changes and introduces no blocking or…
Cmux Browser Automation Off-Main	✅ Passed	PASS: The pull request changes only .github/workflows/cmux-tui-sdks.yml. It adds cache key, restore, conditional build, and save steps for the headless cmux-tui binary. It does not change browser …
Cmux Expensive Synchronous Load	✅ Passed	PASS: The pull request changes only .github/workflows/cmux-tui-sdks.yml. It adds GitHub Actions cache key, restore, build gating, and save steps. It does not contain production Swift changes or add …
Cmux Cache Substitution Correctness	✅ Passed	PASS: The pull request changes only .github/workflows/cmux-tui-sdks.yml. The diff adds CI cache restore/build/save steps and changes no Swift, TypeScript, or JavaScript production code. Therefore, i…
Cmux No Hacky Sleeps	✅ Passed	PASS. The PR changes only .github/workflows/cmux-tui-sdks.yml. The rule explicitly excludes GitHub Actions workflow YAML. The added steps compute a cache key, restore the binary, conditionally build…
Cmux Algorithmic Complexity	✅ Passed	The PR changes only .github/workflows/cmux-tui-sdks.yml. The added shell code performs two fixed git rev-parse lookups and constructs a cache key. It adds no loops, collection scans, sorting, filt…
Cmux Swift Concurrency	✅ Passed	PASS: The pull request changes only .github/workflows/cmux-tui-sdks.yml. The authoritative diff contains no Swift files or Swift code, so the cmux Swift concurrency check is not applicable.
Cmux Swift @Concurrent	✅ Passed	The pull request changes only .github/workflows/cmux-tui-sdks.yml. It introduces no Swift files, Swift functions, call sites, or concurrency annotations. The cmux Swift @concurrent`` check is theref…
Cmux Swift Package Boundaries	✅ Passed	PASS: The pull request changes only .github/workflows/cmux-tui-sdks.yml. The authoritative diff contains no Swift files or production Swift changes, so the Swift package boundary rule is not applica…
Cmux Swiftpm Lockfiles	✅ Passed	PASS. The authoritative PR diff changes only .github/workflows/cmux-tui-sdks.yml. It changes no Package.swift, Package.resolved, .gitignore, or Xcode project file, and it introduces no SwiftPM…
Cmux Swift Logging	✅ Passed	PASS: The pull request changes only .github/workflows/cmux-tui-sdks.yml. It adds GitHub Actions cache key, restore, build condition, and save steps. The diff contains no Swift or app/runtime logging…
Cmux User-Facing Error Privacy	✅ Passed	PASS: The diff only changes .github/workflows/cmux-tui-sdks.yml. It adds internal CI cache-key, restore, build, and save steps. The workflow runs on GitHub Actions push, pull-request, and manual eve…
Cmux Full Internationalization	✅ Passed	PASS: The pull request changes only .github/workflows/cmux-tui-sdks.yml. The added cache key, cache restore/save steps, conditions, and comments are CI configuration and operational documentation. T…
Cmux Swiftui State Layout	✅ Passed	PASS: The pull request changes only .github/workflows/cmux-tui-sdks.yml. The diff adds GitHub Actions cache key, restore, build condition, and save steps. It contains no Swift or SwiftUI code, so it…
Cmux Architecture Rethink	✅ Passed	PASS. The pull request changes only .github/workflows/cmux-tui-sdks.yml. It adds cache key, restore, conditional build, and save steps. It contains no Swift architecture changes and does not introdu…
Cmux Swift Auxiliary Window Close Shortcuts	✅ Passed	The pull request changes only .github/workflows/cmux-tui-sdks.yml. The authoritative diff contains no Swift changes and no cmux-owned window code. The auxiliary-window close-shortcut check is theref…
Cmux Source Artifacts	✅ Passed	PASS. The only changed path is .github/workflows/cmux-tui-sdks.yml, which is a hand-written CI configuration. The diff adds cache restore/save steps for a build artifact used by SDK conformance, but…
Cmux No Test Or Debug Seam In Production Source	✅ Passed	PASS: The pull request changes only .github/workflows/cmux-tui-sdks.yml. It does not change any Swift file under a production Sources/ path, so it cannot introduce a test or debug seam in producti…

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Commit to this branch
• Create a new PR

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