fix(web): let new threads honor the project's default model

[KyeMoon123]

Summary

• The project setting "New threads in this project start with this model. Applies to every checkout in this group." (ProjectSettingsPanel.tsx, writes project.defaultModelSelection) was effectively never applied once any thread anywhere had picked a model.
• New threads are seeded via applyStickyState(draftId) in useHandleNewThread.ts, which pulls from a global, provider-keyed "last used model" (stickyModelSelectionByProvider in composerDraftStore.ts) — not scoped to project or thread. The project default was only ever consulted as a last-resort fallback that's effectively dead once the sticky map is populated (i.e. after the user's very first thread ever).
• This fix applies project.defaultModelSelection whenever there's no carryModelSelection (i.e. no thread/draft currently being viewed to intentionally carry a selection from), across all three new-thread code paths in the hook:
  • Minting a genuinely fresh draft.
  • Reusing a stored-but-empty draft for the project.
  • Reusing the empty draft that's already open.

Test plan

• pnpm run typecheck (apps/web) — passes
• pnpm run lint -- apps/web/src/hooks/useHandleNewThread.ts — passes
• Manual: set a project's default model in Settings, start several threads elsewhere with a different model selected, then create a new thread in that project (via each of: fresh draft, an existing empty draft for the project, and the currently-open empty draft) — each should open with the configured default instead of the last-used model.

Note

Fix new threads to honor the project's default model selection

In useHandleNewThread.ts, when creating or reusing an empty draft without a carried model selection, the handler now applies project.defaultModelSelection with replaceOptions: true to the target draft. This covers three cases: reusing an existing empty draft for a project remap, staying on the current route's empty draft during a context update, and creating a brand new draft.

Risk: The project default overrides any previously stored selection or sticky state on empty drafts.

^{Macroscope summarized 75b13e3.}

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Note

Low Risk
Behavior change is limited to new/reused empty draft initialization in one hook; no auth, persistence, or server API changes.

Overview
New threads in a project now honor the configured default model when the user isn’t carrying a selection from the thread they’re viewing.

useHandleNewThread already seeds drafts from global sticky “last used model” state and only overrides that when carryModelSelection is present. This change adds the same kind of override for project.defaultModelSelection in three paths: resurrecting an empty stored draft, reusing the empty draft already open for that project, and minting a brand-new draft after applyStickyState. In each case it runs only when there is no carried selection, and uses setModelSelection with replaceOptions: true so the project default is a full snapshot (not merged with stale draft options).

Precedence is unchanged for carry-over: if the user is viewing a thread/draft with a model, that selection still wins over both sticky state and the project default.

^{Reviewed by Cursor Bugbot for commit 75b13e3. Bugbot is set up for automated code reviews on this repo. Configure here.}

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[macroscopeapp]

Approvability

Verdict: Approved at 75b13e3

Macroscope's review found this PR approvable — This is a focused bug fix that adds fallback logic to honor project default model selections in new threads. The changes are additive, well-commented, and follow existing patterns in the file. The scope is limited to model selection defaults in thread creation.

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[t3dotgg]

Note

🤖 GPT-5.6 Sol responding on behalf of Theo

We're closing this PR as we clean up the T3 Code backlog. Thank you for taking the time to put this together.

Closing this narrower project-default fix because it still lets a carried model override the project default. #7515, #6593, and #6011 cover the precedence choice more directly and remain open. Keep the fresh and reused draft cases in the selected implementation.

If you believe we closed this in error, please reopen the PR and leave a comment explaining what we missed. If GitHub does not let you reopen it, leave a comment here and we'll take another look.