fix(help): show trace paths as optional

[thymikee]

Summary

agent-device help trace printed trace start <path> | trace stop <path>, which marks the path as required, and its description said "when an explicit path is required". Both paths are optional:

• trace start with no path writes a timestamped trace log named after the session in the daemon's sessions directory (trace-runtime.ts:34, SessionStore.defaultTracePath).
• trace stop <path> moves the finished trace to that path (relocateTraceOutput).

The command schema already declared the path optional (positionalArgs: ['start|stop', 'path?']); only the hand-written usage and description were wrong. This PR:

• changes the usage and list usage to trace start [path] | trace stop [path]
• rewrites the description to say what happens with and without a path. The same text is the MCP tool description, so it uses no CLI placeholders, which command-surface-metadata.test.ts enforces.
• drops the cliDetail line that repeated the wrong rule
• updates the cli-help-topics.test.ts assertion that pinned the wrong usage

Found while trimming commands.md (#3441), which already documents trace start [path].

Validation

• pnpm check:affected --run passed on 5026910.
• cli-help-topics and command-surface-metadata pass (37 tests).
• help trace now prints trace start [path] | trace stop [path].
• Help and metadata text only, so no device runs.

🤖 Generated with Claude Code

[github-actions]

Size Report

Metric	Base	Current	Diff
Installed (including dependencies)	5.17 MB	5.17 MB	-10 B
Package (unpacked)	5.17 MB	5.17 MB	-10 B
Package (download)	1.55 MB	1.55 MB	-9 B

Startup median (7 runs, lower is better):

Scenario	Base	Current	Diff
CLI --version	23.0 ms	21.1 ms	-1.9 ms
CLI --help	56.1 ms	52.9 ms	-3.2 ms

[cubic-dev-ai]

No issues found across 2 files

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[thymikee]

I found no problems in 5026910. The change to show trace paths as optional in the help output looks right. All 19 checks pass and there are no conflicts, so it is ready for review. I did not read the body of defaultTracePath, so I have not checked the "timestamped" wording in the description. I also did not look for generated docs or skills that quote the old usage, beyond a grep that found no copies of the old <path> form.