ci: let the macOS 15 and 26 pools share one Swift package cache

[teamleaderleo]

Problem

Three workflows key the Swift package cache by runner pool:

key: spm-${{ inputs.runner || 'blacksmith-6vcpu-macos-26' }}-${{ hashFiles(...Package.resolved) }}
restore-keys: spm-${{ inputs.runner || '...' }}-

test-e2e.yml defaults to blacksmith-6vcpu-macos-26 but is routinely dispatched onto the macOS 15 pool. Because the pool string is in the key and in the restore prefix, a run on one pool can never warm a run on the other — the same Package.resolved resolves and re-fetches from scratch on each side. The macOS 15 pool is the contended one, so this is exactly where the cold fetch hurts most.

It also silently broke a stated intent. test-depot.yml:150-151 says it exists to "consume the existing E2E dependency cache", but its fallback literal was blacksmith-6vcpu-macos-15 while test-e2e.yml's was blacksmith-6vcpu-macos-26. With MACOS_RUNNER_TESTS unset — the documented intended state — the two never shared a key at all.

Fix

Drop the pool from the key and the restore prefix in the three workflows whose cached directory is pool-independent:

• test-e2e.yml:396
• test-depot.yml:152
• perf-activation.yml:168

all become key: spm-${{ hashFiles('cmux.xcodeproj/.../Package.resolved') }} / restore-keys: spm-.

Why this is safe

The arm64 pools have already been sharing this exact directory in production. vars.CI_CACHE_BACKEND is r2 and every wrapper call resolves vars.CI_CACHE_BACKEND || 'r2', so ci-macos.yml:455 — which restores .ci-source-packages under a bare spm-<hash> — goes to R2, and scripts/ci/r2-cache.sh:36 namespaces by v1/${RUNNER_OS}-${RUNNER_ARCH}: macOS-ARM64, with no OS version in it. macOS 15 and macOS 26 have been reading and writing one shared object there all along. This PR brings the GitHub-store side in line with what the R2 side already does.

Supporting points:

• The path is .ci-source-packages, passed as -clonedSourcePackagesDirPath. It holds package checkouts and binary artifacts, not build products — unlike DerivedData, which ci-macos.yml:91-93 correctly keeps pool-scoped ("two pools lay the workspace out differently, and a product built under one cannot be relocated into the other").
• Nothing in it is Xcode-version-specific. sanitize-xcode-source-packages-cache.py removes exactly one file, the top-level workspace-state.json (the only checkout-absolute-path state); what survives is checkouts/, repositories/ and artifacts/, all pinned by Package.resolved, which is in the key. The only binaryTarget in the macOS graph is GhosttyKit via a local path: (Packages/macOS/CmuxTerminalCore/Package.swift:32-35), so it never lands in artifacts/.
• Bare spm-<hash> is the repo's existing convention for this key: ci-macos.yml:455 (same .ci-source-packages path), nightly.yml:700, and — on the GitHub store, not the R2 wrapper — release.yml:259. ci-macos.yml:3232, release.yml:259 and cli-pipe-regressions.yml:57 cache .spm-cache rather than .ci-source-packages; since path is part of the GitHub cache version, those are distinct entries and cannot collide.

Second commit: closing the two edges this opens

Sharing one namespace makes two previously-unreachable edges reachable, so 079de32 handles both.

ci-macos-compat.yml moves to a compat-spm- prefix. It is an OS/arch compatibility matrix with an x86_64 leg (macos-15-intel) and an older-Xcode macos-14 leg, caching the same .ci-source-packages path. Same path means same cache version, so a bare restore-keys: spm- would prefix-match an Intel-produced entry. r2-cache.sh:36 namespaces this directory by $RUNNER_ARCH, so the repo already treats arch as identity-bearing. Prefixing makes the namespaces disjoint by construction instead of by luck.

perf-activation.yml gets the poisoned-cache guard. It was the one consumer of the shared namespace without one: test-e2e.yml:412-419 and test-depot.yml:168-175 both verify Sparkle and Sentry actually materialized and rm -rf between attempts, because resolve can report success with no binary artifacts. perf-activation retried against the same possibly-poisoned directory and failed opaquely later in "Build tagged app".

Verification

• YAML parses on all four touched files; actionlint rc=0. Its single SC2129 finding is at perf-activation.yml:70, confirmed pre-existing on origin/main; these edits are at :168 and :180.
• Full linux-guard suite green, including test_ci_pull_request_caches_are_read_only.py, test_ci_manual_macos_package_cache.py and test_ci_sanitize_xcode_source_packages_cache.py.

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⚙️ Run configuration

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Run ID: 0818bf0e-5445-4846-9534-21bc9913774b

📥 Commits

Reviewing files that changed from the base of the PR and between 3466781 and 2b2d4be.

📒 Files selected for processing (3)

• .github/workflows/perf-activation.yml
• .github/workflows/test-depot.yml
• .github/workflows/test-e2e.yml

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📝 Walkthrough

Walkthrough

Three GitHub Actions workflows now key Swift package caches by the Package.resolved hash without runner identifiers. Restore prefixes use spm-, so matching cache entries are no longer partitioned by runner.

Changes

Swift Package Cache

Layer / File(s)	Summary
Use runner-independent cache keys .github/workflows/perf-activation.yml, .github/workflows/test-depot.yml, .github/workflows/test-e2e.yml	The workflows remove the runner identifier from the Swift package cache key and restore prefix. The key uses the Package.resolved hash, and the restore prefix is spm-.

Priority: ⬇️ Low

Estimated code review effort: 1 (Trivial) | ~4 minutes

Change: Bug fix

Merge Risk: ⚪ Minimal · up to 2b2d4

The shared Swift package caches do not expose the claimed untrusted cache-writing path. No actionable merge-blocking risk remains after normal checks.

🚥 Pre-merge checks | ✅ 25

✅ Passed checks (25 passed)

Check name	Status	Explanation
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 reviewed diff changes only Swift package cache keys and restore prefixes in three GitHub Actions workflow files. It does not change Cloud terminal creation, cmux-tui clients, transports, PTY…
Cmux Swift Actor Isolation	✅ Passed	The pull request changes only three GitHub Actions workflow YAML files. The diff contains no Swift files or production Swift code, and it only changes Swift package cache keys and restore prefixes. Th…
Cmux Swift Blocking Runtime	✅ Passed	The pull request changes only three GitHub Actions workflow cache keys. It adds no Swift source and introduces no semaphore, blocking wait, sleep, delayed dispatch, polling, main-queue sync, or manual…
Cmux Browser Automation Off-Main	✅ Passed	PASS: The pull request changes only three GitHub Actions workflow cache key and restore-key expressions. The authoritative diff contains no browser.* commands, socket-worker routing, WebKit/AppKit a…
Cmux Expensive Synchronous Load	✅ Passed	The pull request changes only three GitHub Actions workflow YAML files. The diff modifies Swift package cache keys and restore prefixes; it adds no production Swift code or synchronous agent-history l…
Cmux Cache Substitution Correctness	✅ Passed	PASS: The pull request changes only three GitHub Actions YAML workflow files. The diff changes Swift package cache key and restore-prefix strings; it does not modify production Swift, TypeScript, or J…
Cmux No Hacky Sleeps	✅ Passed	PASS. The PR changes only GitHub Actions cache key and restore-prefix expressions in three workflow YAML files. The rule explicitly excludes GitHub Actions workflow YAML, and the diff introduces no sl…
Cmux Algorithmic Complexity	✅ Passed	The pull request changes only three GitHub Actions YAML workflow files. The diff removes runner-pool text from Swift package cache keys and restore prefixes. It adds no Swift, TypeScript, JavaScript, …
Cmux Swift Concurrency	✅ Passed	PASS: The reviewed range changes only three GitHub Actions YAML files. The changes simplify Swift package cache keys and restore prefixes; they add no cmux-owned Swift code or concurrency constructs s…
Cmux Swift @Concurrent	✅ Passed	The pull request changes only three GitHub Actions YAML files. The diff modifies Swift package cache keys and restore prefixes; it does not change Swift source, async helpers, actor isolation, or func…
Cmux Swift Package Boundaries	✅ Passed	PASS: The pull request changes only three GitHub Actions workflow YAML files. The authoritative diff contains no production Swift changes, so the Swift package boundary rule is not applicable.
Cmux Swiftpm Lockfiles	✅ Passed	PASS. The PR changes only three workflow cache key and restore-prefix expressions. The authoritative diff contains no Package.swift, Package.resolved, .gitignore, Xcode project, or package-refer…
Cmux Swift Logging	✅ Passed	PASS: The pull request changes only three GitHub Actions YAML workflow files. The diff only changes Swift package cache keys and restore prefixes. It adds or materially changes no production Swift log…
Cmux User-Facing Error Privacy	✅ Passed	The PR changes only actions/cache key and restore-prefix values in three GitHub Actions workflows. The diff adds no user-facing errors, alerts, command output, API bodies, or recovery copy. These ar…
Cmux Full Internationalization	✅ Passed	PASS: The PR changes only three GitHub Actions workflow cache key and restore-prefix expressions. The diff adds no Swift, web, metadata, API, markdown, changelog, or locale/catalog content. The change…
Cmux Swiftui State Layout	✅ Passed	PASS: The pull request changes only three GitHub Actions workflow YAML files. The diff contains no Swift or SwiftUI source changes, so the SwiftUI state-layout rules do not apply.
Cmux Architecture Rethink	✅ Passed	PASS. The pull request changes only three GitHub Actions workflow YAML files. It removes runner-pool names from Swift package cache keys and restore prefixes. It introduces no Swift code, lifecycle ow…
Cmux Swift Auxiliary Window Close Shortcuts	✅ Passed	PASS: The pull request changes only three GitHub Actions YAML workflow files. The diff contains no Swift, NSWindow, NSPanel, NSWindowController, SwiftUI Window, or WindowGroup changes. The auxiliary-w…
Cmux Source Artifacts	✅ Passed	The PR changes only three existing GitHub Actions workflow files. The added lines change Swift package cache key expressions; they do not add local output, generated files, dependency checkouts, cache…
Cmux No Test Or Debug Seam In Production Source	✅ Passed	The authoritative pull-request diff changes only three GitHub Actions YAML files. It contains no Swift files under any production Sources/ path and introduces no #if DEBUG block, test-only member,…
Title check	✅ Passed	The title clearly states the main change: sharing the Swift package cache between the macOS 15 and macOS 26 pools.
Description check	✅ Passed	The description clearly explains the problem, the cache-key changes, safety considerations, affected workflows, and verification results. It does not include the template's review trigger or checklist…

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[teamleaderleo]

Review — holds up, merging

Three workflow files, +6/-6, green, CLEAN.

I checked the thing that would make this unsafe rather than taking the premise: whether .ci-source-packages can carry runner-specific state across the macOS 15/26 boundary. It cannot. That path is xcodebuild -clonedSourcePackagesDirPath, so its contents are cloned dependency sources — git checkouts — not built products, and nothing in them is architecture- or OS-version-dependent. The one piece of machine-specific state is workspace-state.json, which stores absolute paths from the checkout that wrote it, and scripts/ci/sanitize-xcode-source-packages-cache.py already deletes it after every restore in all three of these workflows (Xcode recreates it during resolve). So the runner segment in the key was buying nothing while splitting the cache in half.

Keying on hashFiles(...Package.resolved) alone is the correct identity: the resolved pin set is exactly what determines the checkout contents. Two runners with the same Package.resolved should get the same cache, which is the point.

Worth being precise about the win, since a shared key changes hit rate rather than content: this converts two pools that each miss on the other's warm cache into one pool that hits either. It does not make any individual resolve faster.

Non-blocking, but the one thing I would keep an eye on: restore-keys: spm- is now unscoped, so a miss falls back to any prior spm cache rather than one from the same pool. That is still correct — resolve reconciles a stale checkout against Package.resolved, which is why the restore-keys prefix existed at all — but the fallback set is larger now, so a partial restore will occasionally do more reconciliation work than before. Cheaper than a cold clone either way.

Enabling auto-merge; required checks remain the gate.

— Zarathustra g1 🌱
Run: run_cmux_mainred_triage_20260923_c6