Summary

Gut the Mattermost model-picker UI. Parallel pattern to the Discord gut in #2414 — both are triggered by /model and /models slash commands and depended on model-provider data sources that were removed during the #2337 cascade. Per Middleware Boundary Principle, model selection is owned by CLI runtimes, not RemoteClaw middleware.

Mattermost is a published extension package (@remoteclaw/mattermost) with a live slash-http integration. This gut removes the model-picker handler path while preserving the rest of the channel plugin.

Current state

Model-picker surface in Mattermost:

• extensions/mattermost/src/mattermost/model-picker.ts (360 LoC) — defines resolveMattermostModelPickerEntry, resolveMattermostModelPickerCurrentModel, parseMattermostModelPickerContext, MattermostModelPickerState, MattermostModelPickerEntry, etc.
• extensions/mattermost/src/mattermost/model-picker.test.ts (155 LoC) — tests for above
• extensions/mattermost/src/mattermost/slash-http.ts:30-32, 388 — imports + calls resolveMattermostModelPickerEntry(commandText) in slash-command flow
• extensions/mattermost/src/mattermost/monitor.ts:56, 496, 760-880 — parseMattermostModelPickerContext import, handleModelPickerInteraction handler, buildModelPickerProps, updateModelPickerPost, plus handleInteraction: handleModelPickerInteraction wiring

Files

Protocol

1. Delete model-picker.ts + model-picker.test.ts
2. Strip model-picker code paths from slash-http.ts — /model and /models will fall through to normal slash-command handling (verify the resulting behavior: likely unknown-command response, which is correct)
3. Strip model-picker code paths from monitor.ts — stale model-picker buttons in old Mattermost posts will no longer have a handler; they fall to default interaction handling (acknowledge/noop)
4. Run pnpm check + pnpm test + node scripts/check-no-zombie-imports.mjs
5. Scrub scripts/data/zombie-import-allowlist.json if any stale entries reference the deleted paths

AC

• 2 files deleted (model-picker.ts, model-picker.test.ts)
• slash-http.ts + monitor.ts modified — grep ModelPicker|model-picker|modelPicker in extensions/mattermost/ returns only migration/detection comments, no live references
• pnpm check passes
• pnpm test passes
• node scripts/check-no-zombie-imports.mjs passes
• CI zombie-import-gate passes
• Mattermost channel adapter still functional — monitor still runs, slash-http still handles non-model commands, no new throwing-stub callers introduced

Rationale

Per Middleware Boundary Principle, model selection is a CLI-agent concern — Claude, Gemini, Codex, and OpenCode each handle their own model choice. The model-picker UI was inherited from the Pi-era provider catalog (gutted in #2337 across src/agents/model-catalog.ts, src/gateway/server-methods/models.ts, etc.). The Mattermost channel UI is the last surface in this repo holding onto the pattern and should be removed for consistency.

Relation to #2414

#2414 handles the Discord parallel (dead but compile-linked model-picker inside src/discord/monitor/). This issue is filed as a sibling — same pattern, different channel package, independent blast radius. Should land after #2414 or alongside it.