fix(web): keep worktree default when switching a draft's machine

apps/web/src/composerDraftStore.test.ts

@@ -1103,13 +1103,14 @@ describe("composerDraftStore project draft thread mapping", () => {
     });
   });
 
-  it("clears branch and worktree context when remapping a draft to another environment", () => {
+  it("clears branch and worktree but keeps env mode when remapping a draft to another environment", () => {
     const store = useComposerDraftStore.getState();
     store.setProjectDraftThreadId(projectRef, draftId, {
       threadId,
       branch: "feature/local-only",
       worktreePath: "/tmp/local-worktree",
       envMode: "worktree",
+      startFromOrigin: true,
     });
 
     store.setLogicalProjectDraftThreadId(scopedProjectKey(projectRef), remoteProjectRef, draftId, {
@@ -1121,17 +1122,19 @@ describe("composerDraftStore project draft thread mapping", () => {
       projectId,
       branch: null,
       worktreePath: null,
-      envMode: "local",
+      envMode: "worktree",
+      startFromOrigin: true,
     });
   });
 
-  it("clears branch and worktree context when changing a draft thread project ref", () => {
+  it("clears branch and worktree but keeps env mode when changing a draft thread project ref", () => {
     const store = useComposerDraftStore.getState();
     store.setProjectDraftThreadId(projectRef, draftId, {
       threadId,
       branch: "feature/local-only",
       worktreePath: "/tmp/local-worktree",
       envMode: "worktree",
+      startFromOrigin: true,
     });
 
     store.setDraftThreadContext(draftId, {
@@ -1143,7 +1146,8 @@ describe("composerDraftStore project draft thread mapping", () => {
       projectId,
       branch: null,
       worktreePath: null,
-      envMode: "local",
+      envMode: "worktree",
+      startFromOrigin: true,
     });
   });
 });

apps/web/src/composerDraftStore.ts

@@ -1340,6 +1340,10 @@ function createDraftThreadState(
     interactionMode?: ProviderInteractionMode;
   },
 ): DraftThreadState {
+  // A project change (including switching environments within a logical
+  // project) invalidates machine-specific context: the branch may not exist
+  // there and the worktree path certainly doesn't. The user's *intent* —
+  // env mode and start-from-origin — is machine-independent and carries.
   const projectChanged =
     existingThread !== undefined &&
     (existingThread.environmentId !== projectRef.environmentId ||
@@ -1358,9 +1362,7 @@ function createDraftThreadState(
       : (options.branch ?? null);
   const nextStartFromOrigin =
     options?.startFromOrigin === undefined
-      ? projectChanged
-        ? false
-        : (existingThread?.startFromOrigin ?? false)
+      ? (existingThread?.startFromOrigin ?? false)
       : options.startFromOrigin;
   return {
     threadId,
@@ -1374,12 +1376,7 @@ function createDraftThreadState(
     branch: nextBranch,
     worktreePath: nextWorktreePath,
     envMode:
-      options?.envMode ??
-      (nextWorktreePath
-        ? "worktree"
-        : projectChanged
-          ? "local"
-          : (existingThread?.envMode ?? "local")),
+      options?.envMode ?? (nextWorktreePath ? "worktree" : (existingThread?.envMode ?? "local")),
     startFromOrigin: nextStartFromOrigin,
     promotedTo: null,
   };
@@ -2343,6 +2340,9 @@ const composerDraftStore = create<ComposerDraftStoreState>()(
             ) {
               return state;
             }
+            // Mirrors createDraftThreadState: a project/environment change
+            // drops machine-specific context (branch, worktree path) but
+            // keeps the user's env mode and start-from-origin intent.
             const projectChanged =
               nextProjectRef.environmentId !== existing.environmentId ||
               nextProjectRef.projectId !== existing.projectId;
@@ -2360,9 +2360,7 @@ const composerDraftStore = create<ComposerDraftStoreState>()(
                 : (options.branch ?? null);
             const nextStartFromOrigin =
               options.startFromOrigin === undefined
-                ? projectChanged
-                  ? false
-                  : existing.startFromOrigin
+                ? existing.startFromOrigin
                 : options.startFromOrigin;
             const nextDraftThread: DraftThreadState = {
               threadId: existing.threadId,
@@ -2378,12 +2376,7 @@ const composerDraftStore = create<ComposerDraftStoreState>()(
               branch: nextBranch,
               worktreePath: nextWorktreePath,
               envMode:
-                options.envMode ??
-                (nextWorktreePath
-                  ? "worktree"
-                  : projectChanged
-                    ? "local"
-                    : (existing.envMode ?? "local")),
+                options.envMode ?? (nextWorktreePath ? "worktree" : (existing.envMode ?? "local")),
               startFromOrigin: nextStartFromOrigin,
               promotedTo: existing.promotedTo ?? null,
             };

apps/web/src/hooks/useHandleNewThread.ts

@@ -183,8 +183,7 @@ export function useNewThreadHandler() {
           // The workspace context must also ride along here: when projectRef
           // targets a different physical member of the logical project,
           // createDraftThreadState treats the remap as a project change and
-          // would otherwise wipe branch/worktree and force "local" mode,
-          // undoing the write above.
+          // would otherwise wipe branch/worktree, undoing the write above.
           setLogicalProjectDraftThreadId(
             logicalProjectKey,
             projectRef,