Apple Intelligence as an on-device Command Mode provider (macOS 27+)

[BenjaminPrice]

I'd like to propose a narrow, Command Mode-only return of Apple Intelligence and ask whether the scope is acceptable before I open a PR.

Proposal

• Add one row to the Command Mode model picker: "Apple Intelligence · System Language Model". It shows only on macOS 27+ when the model reports .available.
• The model drives the existing execute_terminal_command tool. The tool only captures each call, so the current agent loop still runs, confirms, cancels, and caps every command.

Not in scope

• Dictation, Edit/Rewrite mode, AI Enhancement, and Meeting Summary don't change and never list it.
• It is never used as a fallback, so [BUG] selected provider silently falls back to Apple Intelligence for enhancement despite fluid-1 runtime being loaded/cached #561 can't come back.

Why

• Command Mode with no API key, no cost, and nothing leaving the Mac.
• macOS 27 ships a rebuilt on-device model that Apple says is better at tool calling, which is what Command Mode needs. The macOS 26 model was weak at multi-step tool use, so I've left macOS 26 and earlier out.

Evidence so far (macOS 27.2, Apple Silicon)

• A 3-step task ("create a folder, add a file with content, list it") completed in 5 of 5 runs, in 5–6 turns and 11–13 s each, using at most about 1.4K of the 8K-token context window.
• In all 3 delete tests the model emitted rm as a tool call, so the existing confirmation card catches it.
• Manual tests of disk usage, multi-step file tasks, follow-ups, delete with confirmation, Escape mid-request, and turning Apple Intelligence off all behaved correctly.

Size
The implementation is ready on a fork branch: https://github.com/BenjaminPrice/FluidVoice/tree/feat/command-mode-apple-intelligence - it adds 242 lines of source (207 in one new file) and 118 lines of tests. That's about a fifth of #1058.

Related: #1055, #604, #561, #1058.

Would you accept a PR with this scope? I'm happy to change it based on your feedback.

[BenjaminPrice]

Update: the maintainer approved the Command Mode-only scope on Discord: "I'm down if you want to just add it for the command mode." (message)

• Tracking issue: [FEATURE] Apple Intelligence as an on-device Command Mode provider (macOS 27+) #1299
• PR: Add Apple Intelligence as an on-device Command Mode provider #1300, rebased on current main

The scope is unchanged from the proposal above. Dictation, Edit/Rewrite, AI Enhancement, and Meeting Summary are untouched.