fix(web): remember Composer Fast mode across new chats

[aravhawk]

What Changed

• Default Cursor Composer fastMode to Normal when the user has not explicitly chosen Fast, instead of using Cursor ACP’s provider-reported default.
• Preserve sticky fastMode options when switching models, so changing to Composer 2.5 (or another model) no longer clears the last Fast/Normal choice.
• Added tests for default dispatch behavior and sticky option preservation.

Why

Selecting Composer 2.5 in a new chat was defaulting to Fast mode every time, even after manually turning it off. Cursor ACP reports fastMode: true as the provider default, and T3 was treating that as the user’s selection. Model switches also cleared sticky trait options, so the last manual Fast/Normal choice did not carry into new chats.

This keeps Fast mode opt-in and remembers the user’s last manual choice across new chats and model changes.

UI Changes

N/A — behavior-only change. New Composer chats start in Normal unless the user previously chose Fast, and switching models no longer resets Fast/Normal to the provider default.

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for any UI changes
• I included a video for animation/interaction changes

Note

Fix Composer Fast mode to persist across new chats

• Adds withImplicitFastModeDefault in composerProviderState.tsx to inject fastMode=false when a model exposes the fast mode option but the user has made no explicit selection, preventing the provider default from being silently applied.
• Updates setStickyModelSelection in composerDraftStore.ts to retain existing provider options when a new sticky model selection omits them, so fast mode preference survives model changes and new chats.
• Behavioral Change: Composer state now always includes an explicit fastMode=false entry when the model supports fast mode and no user selection exists, rather than leaving it unset.

^{Macroscope summarized c1a38de.}

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[macroscopeapp]

Approvability

Verdict: Approved

Self-contained UX fix that ensures Composer Fast mode preferences persist across new chats. Changes are well-tested with comprehensive unit tests and limited in scope to composer state management. The open review comment appears to be based on an incorrect reading of the code.

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Apply implicit Fast default to trait controls too

When Cursor reports fastMode.currentValue === true and the user has no explicit selection, this implicit false is only fed into getComposerProviderState for dispatch. The rendered trait controls still receive the raw modelOptions via renderProviderTraitsPicker/MenuContent, so TraitsPicker builds descriptors from the provider default and shows the toggle/label as Fast even though the send path dispatches Normal. This leaves new Composer chats in a misleading state until the user toggles Fast/Normal.

Useful? React with 👍 / 👎.

Dismissing prior approval to re-evaluate c1a38de