Include claude attach in claude_builtin_command_names

[steve-wisdom]

Problem

claude attach <id> is a real Claude Code subcommand — the attach door printed for --bg background sessions — but it's hidden from claude --help, so it never made it into claude_builtin_command_name in cmux-claude-wrapper. Inside a cmux surface the wrapper therefore classifies it as a session entrypoint and execs the real CLI as:

claude --session-id <fresh-uuid> --settings '{...hooks...}' attach <id>

The CLI eats the injected flags and reads attach as the [prompt] positional: instead of attaching to the running background session, it mints a brand-new session with "attach" pre-filled in the composer.

Repro (any cmux surface, Claude Code ≥ 2.1.x): claude attach <any-id> → new session with "attach" in the prompt box, instead of No job matching '<any-id>' / attaching.

Fix

Add attach to the builtin-command list so it passes through untouched, like agents/mcp/etc. Hook injection is meaningless for attach anyway — hooks live in the already-running background writer process, and a fresh --session-id on an attach invocation is exactly the bug.

Two-commit structure per the regression-test policy: commit 1 adds the failing test (test_hidden_attach_subcommand_bypasses_hook_injection in tests/test_claude_wrapper_hooks.py), commit 2 the one-word fix. Full wrapper suite passes locally.

🤖 Generated with Claude Code

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Summary by cubic

Passes the hidden claude attach <id> subcommand through the cmux-claude-wrapper so attach works again in cmux surfaces. Previously the wrapper injected --session-id/--settings (and NODE_OPTIONS), so the CLI treated attach as the prompt and started a new session; now it receives attach <id> untouched and attaches (or errors) as expected.

• Adds attach to builtin command detection in claude_builtin_command_name, preventing --session-id, --settings, and NODE_OPTIONS injection.
• Adds regression test test_hidden_attach_subcommand_bypasses_hook_injection.
• Review focus: the one-word addition in Resources/bin/cmux-claude-wrapper; no changes to other subcommands or hook behavior.
• No migration required; only affects claude attach <id> invocations in cmux surfaces.

^{Written for commit 97cbc20. Summary will update on new commits.}

Summary by CodeRabbit

• Bug Fixes

  • Fixed the claude attach command so it opens an existing session without being treated as a new prompt.
  • Preserved command arguments and prevented unintended hook, settings, session, and runtime option injection.

• Tests

  • Added regression coverage for attaching to existing sessions.

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[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

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Run ID: 066132b2-beae-4745-86ef-0b0c5540d90c

📥 Commits

Reviewing files that changed from the base of the PR and between bddca3f and 97cbc20.

📒 Files selected for processing (1)

• Resources/bin/cmux-claude-wrapper

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📝 Walkthrough

Walkthrough

The Claude wrapper now recognizes attach as a built-in command. The regression test confirms that claude attach <id> preserves arguments and bypasses hook, session-ID, settings, and NODE_OPTIONS injection.

Changes

Claude attach command handling

Layer / File(s)	Summary
Recognize and validate attach passthrough Resources/bin/cmux-claude-wrapper, tests/test_claude_wrapper_hooks.py	The wrapper recognizes attach as a built-in command. Tests verify argument passthrough and the absence of hook, session-ID, settings, and NODE_OPTIONS injection. The test is registered in main().

Estimated code review effort: 2 (Simple) | ~10 minutes

Mergeability Score: ⚪ Minimal · up to 97cbc

This narrowly changes claude attach <id> handling so it passes through without session-flag injection, with no actionable merge-blocking risk remaining after normal checks and review.

Suggested reviewers: austinywang, lawrencecchen

🚥 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.
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 Swift Actor Isolation	✅ Passed	The PR diff changes only the shell wrapper and adds no Swift declarations or production Swift code, so it cannot introduce Swift 6 actor-isolation mistakes.
Cmux Swift Blocking Runtime	✅ Passed	The two-commit diff changes only a shell wrapper and a Python regression test; it introduces no production Swift code or blocking runtime synchronization.
Cmux Browser Automation Off-Main	✅ Passed	The PR changes only the Claude shell wrapper and its Python regression test; it introduces no browser.* socket command, WebKit/AppKit access, worker routing, or main-actor routing change.
Cmux Expensive Synchronous Load	✅ Passed	The actual diff changes only the non-Swift shell wrapper. It adds no Swift code or synchronous agent-history load on a main-actor or interactive path.
Cmux Cache Substitution Correctness	✅ Passed	The diff changes only a Bash wrapper and a Python test; it contains no production Swift, TypeScript, or JavaScript cache substitution.
Cmux No Hacky Sleeps	✅ Passed	The diff only adds attach to a shell command list and adds a regression test; no sleep, timer, polling, delay, or wall-clock wait was introduced.
Cmux Algorithmic Complexity	✅ Passed	The diff adds one name to a small fixed shell command list; it introduces no scalable collection scan or slower algorithm. The added regression test is test-only.
Cmux Swift Concurrency	✅ Passed	The complete PR range changes only the Claude wrapper and its Python test; it contains no Swift files or Swift concurrency patterns.
Cmux Swift @Concurrent	✅ Passed	The complete PR range changes only the Claude wrapper and its Python test; no Swift files, async functions, or Swift call sites changed.
Cmux Swift Package Boundaries	✅ Passed	The PR changes only a shell wrapper and a Python regression test; it introduces no production Swift changes or Swift package-boundary violation.
Cmux Swiftpm Lockfiles	✅ Passed	The PR diff changes only the Claude wrapper and its Python regression test; it adds no Package.swift, Package.resolved, Xcode project, .gitignore, workflow, or dependency changes.
Cmux Swift Logging	✅ Passed	The full PR diff changes only the Claude shell wrapper and a Python test; it adds no production Swift code or Swift logging.
Cmux User-Facing Error Privacy	✅ Passed	The production diff only adds attach to command classification; it adds no user-facing error, alert, output, or recovery text. The added regression test is explicitly allowed.
Cmux Full Internationalization	✅ Passed	The diff adds only the literal attach command token and a regression test; it changes no user-facing Swift/web/catalog text, and command names/tests are explicitly allowed.
Cmux Swiftui State Layout	✅ Passed	The PR changes only the shell wrapper and its Python regression test; the diff contains no Swift or SwiftUI files, state, layout, or render code.
Cmux Architecture Rethink	✅ Passed	The diff changes one Bash wrapper line and adds no Swift files or Swift lifecycle code; the custom Swift architecture failure conditions are not applicable.
Cmux Swift Auxiliary Window Close Shortcuts	✅ Passed	The PR changes only a shell wrapper and a Python test; the PR range contains no Swift, AppKit, or SwiftUI window changes covered by this check.
Cmux Source Artifacts	✅ Passed	The PR changes only the hand-written wrapper source and a regression test; no local, generated, cache, scratch, build, or copied artifact paths appear in the diff.
Cmux No Test Or Debug Seam In Production Source	✅ Passed	The PR diff contains only Resources/bin/cmux-claude-wrapper and tests/test_claude_wrapper_hooks.py; it changes no Swift file under a production Sources/ path.
Cmux No Ambient Global State	✅ Passed	The PR changes only the Bash wrapper and its Python regression test; the two-commit diff contains no Swift production changes, so this check is inapplicable.
Title check	✅ Passed	The title directly identifies the addition of attach to the Claude built-in command list, which is the primary code change.
Description check	✅ Passed	The description clearly explains the problem, fix, affected behavior, and regression testing, but omits the template checklist and review-trigger sections.

✨ Finishing Touches

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• Create PR with unit tests

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[steve-wisdom]

Superseded by #10117 — reopened from my personal account.