Built-in /resume silently shadows user custom command (~/.claude/commands/resume.md) — undocumented precedence, no disambiguation

## Summary

A user-level custom command at `~/.claude/commands/resume.md` is silently shadowed by the built-in `/resume` (conversation picker). Typing `/resume` opens the built-in picker; the custom command is unreachable. There is no error, no disambiguation UI, and no documented precedence rule for built-in-vs-custom name collisions.

## Environment

- Claude Code v2.1.172 (Windows 11, native install; also reproduced via the desktop app surface)
- Custom command: `~/.claude/commands/resume.md` (a personal session-checkpoint restore command, paired with a working `/pause` custom command)

## Repro

1. Create `~/.claude/commands/resume.md` with any instructions.
2. Type `/resume` in the composer.
3. The built-in conversation picker opens ("No sessions match your search" when empty). The custom command markdown is never dispatched.

Control: a custom command with a non-colliding name (e.g. `/pause`) in the same directory dispatches normally, confirming custom-command dispatch works and the failure is specific to the name collision.

## Version bracket (local forensics)

Grepping cached release bundles for the built-in picker's empty-state string "No sessions match":

| Version | Bundle date | String present |
|---|---|---|
| 2.1.25 | 2026-01-29 | no |
| 2.1.97 | 2026-04-08 | yes |
| 2.1.172 (running) | 2026-06-10 | yes |

So the built-in picker (and the shadowing) arrived between 2.1.25 and 2.1.97. No changelog entry documents the precedence behavior.

## Docs gap

- `commands.md` lists `/resume` as built-in but says nothing about collisions with custom commands.
- `skills.md` ("When skills share the same name") documents skill-vs-skill and skill-vs-custom-command precedence, but not built-in-command-vs-custom precedence.
- No namespacing (`/user:resume`), no "(user)"-labeled menu entry, and no setting appears to exist to reach the shadowed custom command.

## Expected

One of:
1. Custom commands take precedence over built-ins (matching the spirit of the v2.1.228 change "Hardened skills synced from claude.ai: they no longer shadow local commands"), or
2. A documented disambiguation path (namespaced invocation or a labeled second entry in the slash menu), or
3. At minimum: documented precedence in `commands.md`/`skills.md`, and a warning at startup or in `/doctor` when a user/project command is shadowed by a built-in.

## Actual

The built-in wins silently. The user's workflow broke with no signal; diagnosing required grepping release bundles to establish when the built-in appeared.

## Workaround used

Renamed the custom command to a non-colliding name (`/unpause`).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Start by reading commands.md's built-in command list and skills.md's precedence section, then reproduce the /resume collision using the steps in the issue. Establish the intended built-in-versus-custom precedence with maintainers and document the resulting behavior or supported disambiguation path; done when the collision is unambiguous to users.

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