feature: Allow model and harness selection before submitting implementation in a new thread

[thehorse2000]

What Changed

onImplementPlanInNewThread in ChatView.tsx now navigates to a new draft thread with the implementation prompt pre-filled in the composer, instead of immediately creating a server thread and auto-submitting.

A single new store hook extraction (applyStickyState) was added alongside the existing composer draft hooks.

Why

Previously, "Implement in a new thread" locked the user into whatever model and harness were active on the plan thread — there was no opportunity to change them before the implementation run started.

Plan generation and implementation often benefit from different models or access modes (e.g. plan with a reasoning model under Supervised, implement with a faster model under Full access).

Using the existing draft-thread flow solves this cleanly: the draft composer already exposes the model picker and harness selector, so no new UI is needed. The implementation prompt is pre-filled so the user can review it, adjust settings, and submit when ready.

UI Changes

Before: Clicking "Implement in a new thread" immediately starts the implementation run in a new thread — the user arrives mid-execution with no chance to change the model or harness.

After: Clicking "Implement in a new thread" opens a new draft thread with the implementation prompt pre-filled in the composer. The user can change the model, harness
(Supervised / Auto-accept / Full access), or edit the prompt before manually submitting.

Monosnap.screencast.2026-04-10.11-25-14.mp4

Checklist

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

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Note

Medium Risk
Changes the “Implement in a new thread” flow from immediate server thread creation/dispatch to creating a local draft and navigating, which may affect users’ expectations and any downstream logic that assumed an implementation turn starts automatically.

Overview
Updates ChatView so “Implement in a new thread” now creates a new draft thread, pre-fills the implementation prompt, applies sticky composer settings (e.g. model/provider), and navigates to /draft/$draftId instead of creating a server thread and auto-submitting the first turn.

This removes the orchestration thread.create/thread.turn.start dispatch (and related error/cleanup handling) from that action, letting users adjust model/runtime/interaction settings before manually sending.

^{Reviewed by Cursor Bugbot for commit ef214d1. Bugbot is set up for automated code reviews on this repo. Configure here.}

Note

Navigate to a draft thread on 'implement plan in new thread' to allow model and harness selection

• Previously, onImplementPlanInNewThread in ChatView.tsx immediately created a server thread and started a turn via orchestration APIs.
• Now it creates a local draft thread, applies composer sticky state, sets the implementation prompt, and navigates to the draft route — letting the user choose a model and harness before submitting.
• Behavioral Change: The action no longer triggers server-side thread creation or turn execution; instead it redirects to a draft view with the prompt pre-filled.

^{Macroscope summarized ef214d1.}

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[cursor]

Cursor Bugbot has reviewed your changes and found 2 potential issues.

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^{Reviewed by Cursor Bugbot for commit ef214d1. Configure here.}

[cursor]

Implementation thread loses plan source linkage

High Severity

The old onImplementPlanInNewThread explicitly sent sourceProposedPlan: { threadId, planId } in the thread.turn.start command, linking the implementation thread to its originating plan. The new flow navigates to a draft thread, where upon submission the regular onSend path runs — but that path's thread.turn.start (around the bootstrap flow) never includes sourceProposedPlan. The onSubmitPlanFollowUp path does include it, but only fires on same-thread plan follow-ups where activeProposedPlan is non-null. On the draft thread, activeProposedPlan is always null since the draft has no proposed plans. This breaks server-side plan-to-implementation tracking and client-side features like the plan sidebar step display.

Additional Locations (1)

• apps/web/src/components/ChatView.tsx#L2662-L2678

 

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[thehorse2000]

This is a good point but will increase PR scope, let me know if must be done in this scope.

[cursor]

Existing project draft silently discarded on implement

Medium Severity

onImplementPlanInNewThread always creates a fresh nextDraftId and calls setLogicalProjectDraftThreadId without first checking whether a draft already exists for the logical project. setLogicalProjectDraftThreadId replaces the logical-project-to-draft mapping and deletes the previous draft's thread state and composer content if it's no longer referenced. If the user had an in-progress draft with unsaved content for the same project, that content is silently destroyed. The existing openOrReuseProjectDraftThread and useHandleNewThread both check for and reuse existing drafts to avoid this.

 

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[macroscopeapp]

Approvability

Verdict: Needs human review

This PR introduces a feature change to implementation thread creation workflow with significant runtime behavior modifications. Two unresolved review comments identify substantive bugs: loss of plan source linkage (high severity) and silent draft data loss (medium severity). These issues need to be addressed before merging.

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