Add tee OutputDestination for live + captured streaming#21
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Add OutputDestination.tee, which forwards a command's stream to the parent process's stdout/stderr in real time while also capturing it in memory for ShellOutput. This serves long-running commands (e.g. a multi-minute build) that need live console progress and the full captured text for post-run parsing. Implemented entirely in routeData: .tee mirrors .capture (so bytes count toward the output limit identically) plus a live write through a shared NSLock-guarded TeeSink so concurrent stdout/stderr tee writes can't interleave mid-buffer. .capture/.discard/.file are unchanged, and openFileHandleIfNeeded still returns nil for .tee. Add a serialized executor test suite covering capture, live streaming, stdout+stderr interleaving, and output-limit enforcement. The test helper redirects real STDOUT/STDERR FDs via dup/dup2, guarded by the Darwin/Glibc conditional import the repo already uses for Linux CI.
swift-corelibs-foundation's FileManager.createFile is not annotated @discardableResult (unlike Apple's Foundation), so the unused Bool result tripped -warnings-as-errors on the Linux CI matrix only.
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Summary
Adds
OutputDestination.tee, which forwards a command's stream to the parent process's stdout/stderr in real time and captures it in memory forShellOutput. This serves long-running commands (e.g. a multi-minute build) that need live console progress while still needing the full captured text for post-run parsing — previously only.capture(in-memory, surfaced after exit),.discard, and.fileexisted.Changes
OutputDestination.swift: newcase teewith doc comment + a.teeusage example in the type-level docs. Enum remainsSendable, Equatableautomatically.SubprocessExecutor.swift: handle.teeinrouteData(the single routing chokepoint) — it mirrors.capture(so captured bytes count toward the output limit identically) plus a live write. Live writes go through a sharedNSLock-guardedTeeSink(an@unchecked Sendablewrapper, consistent withFileDescriptorClosure) so concurrent stdout/stderr tee writes can't interleave mid-buffer..capture/.discard/.fileare byte-for-byte unchanged;openFileHandleIfNeededstill returnsnilfor.tee.OutputDestinationTeeTests.swift(new,.serializedsuite): capture still populatesShellOutput; live bytes reach the parent stdout; stdout+stderr both.teeinterleave without corruption (lock smoke test);.teehonorsoutputLimit→outputLimitExceeded. The helper redirects realSTDOUT/STDERRFDs viadup/dup2..claude/skills/swiftyshell.md: updated theOutputDestinationAPI reference to include.teeand theEquatableconformance.Testing
swift test --enable-all-traits(full surface) — 399 tests, 42 suites passswift test(default = Core only) — 83 tests passAlso:
swift-format lint --strictclean on all touched files;Scripts/validate-traits.swiftandScripts/validate-docc-coverage.swiftpass; DocC builds cleanly.Notes
FileHandle.standardOutput/.standardError,NSLock). The test helper's POSIX calls (dup/dup2/close/STDOUT_FILENO) are guarded by the same#if canImport(Darwin) … #elseif canImport(Glibc)patternSpawnTests.swiftalready uses in Linux CI. Verified locally on macOS; the CI matrix confirms Linux.-warnings-as-errorsruns hit a pre-existingconflicting options '-warnings-as-errors' and '-suppress-warnings'error while building theswift-systemdependency (reproducible on cleanmain, an Xcode-beta/toolchain issue) — gates were run without that flag locally..tee.