feat: support fast worktree-backed session flows

Add a directory-created fast path for worktree creation so session and send flows can continue once the target directory exists while Git attachment and bootstrap finish in the background.

Track bootstrap status explicitly in shared UI contracts, including pending, ready, and failed states. Background watchers now surface failures and timeouts, update stored worktree metadata, and keep web and VS Code runtime behavior in parity.

Move GitHub issue/PR worktree sessions and assistant-answer fork sessions onto the unified send path so provider, model, agent, and variant selections are preserved. The assistant-answer fork dialog can optionally create a worktree outside VS Code.

Make worktree deletion dialogs close after linked-session cleanup while removing the worktree in the background, and clean up failed fast-create artifacts safely without recursively deleting user or agent-written files.

Validation: bun test packages/ui/src/lib/worktrees/worktreeBootstrap.test.ts packages/ui/src/lib/worktrees/worktreeManager.test.ts; bun run type-check; bun run lint.

packages/ui/src/components/session/GitHubIssuePickerDialog.tsx

@@ -19,10 +19,8 @@ import { useSessionUIStore } from '@/sync/session-ui-store';
 import { useSelectionStore } from '@/sync/selection-store';
 import * as sessionActions from '@/sync/session-actions';
 import { useConfigStore } from '@/stores/useConfigStore';
-import { useContextStore } from '@/stores/contextStore';
 import { useUIStore } from '@/stores/useUIStore';
 import { useGitHubAuthStore } from '@/stores/useGitHubAuthStore';
-import { opencodeClient } from '@/lib/opencode/client';
 import { renderMagicPrompt } from '@/lib/magicPrompts';
 import { parseModelIdentifier } from '@/lib/modelIdentifier';
 import { useDeviceInfo } from '@/lib/device';
@@ -248,9 +246,9 @@ export function GitHubIssuePickerDialog({
   const resolveDefaultVariant = React.useCallback((providerID: string, modelID: string): string | undefined => {
     const configState = useConfigStore.getState();
     const settingsDefaultVariant = configState.settingsDefaultVariant;
-    if (!settingsDefaultVariant) {
-      return undefined;
-    }
+    const currentVariant = configState.currentProviderId === providerID && configState.currentModelId === modelID
+      ? configState.currentVariant
+      : undefined;
 
     const provider = configState.providers.find((p) => p.id === providerID);
     const model = provider?.models.find((m: Record<string, unknown>) => (m as { id?: string }).id === modelID) as
@@ -258,12 +256,15 @@ export function GitHubIssuePickerDialog({
       | undefined;
     const variants = model?.variants;
     if (!variants) {
-      return undefined;
+      return settingsDefaultVariant || currentVariant || undefined;
     }
-    if (!Object.prototype.hasOwnProperty.call(variants, settingsDefaultVariant)) {
-      return undefined;
+    if (settingsDefaultVariant && Object.prototype.hasOwnProperty.call(variants, settingsDefaultVariant)) {
+      return settingsDefaultVariant;
     }
-    return settingsDefaultVariant;
+    if (currentVariant && Object.prototype.hasOwnProperty.call(variants, currentVariant)) {
+      return currentVariant;
+    }
+    return undefined;
   }, []);
 
   const startSession = React.useCallback(async (issueNumber: number, sourceRepo?: GitHubRepoSelector | null) => {
@@ -366,12 +367,14 @@ export function GitHubIssuePickerDialog({
 
       const sessionTitle = `#${issue.number} ${issue.title}`.trim();
 
-      const { sessionId, sessionDirectory } = await (async () => {
+      const { sessionId } = await (async () => {
         if (createInWorktree) {
           const preferred = `issue-${issue.number}-${generateBranchSlug()}`;
           const created = await createWorktreeSessionForNewBranch(
             projectDirectory,
-            preferred
+            preferred,
+            undefined,
+            { returnAfterDirectoryCreated: true }
           );
           if (!created?.id) {
             throw new Error('Failed to create worktree session');
@@ -412,64 +415,27 @@ export function GitHubIssuePickerDialog({
 
       const variant = resolveDefaultVariant(providerID, modelID);
 
-      try {
-        useContextStore.getState().saveSessionModelSelection(sessionId, providerID, modelID);
-      } catch {
-        // ignore
-      }
-
-      if (agentName) {
-        try {
-          configState.setAgent(agentName);
-        } catch {
-          // ignore
-        }
-
-        try {
-          useContextStore.getState().saveSessionAgentSelection(sessionId, agentName);
-        } catch {
-          // ignore
-        }
-
-        try {
-          useContextStore.getState().saveAgentModelForSession(sessionId, agentName, providerID, modelID);
-        } catch {
-          // ignore
-        }
-
-        if (variant !== undefined) {
-          try {
-            configState.setCurrentVariant(variant);
-          } catch {
-            // ignore
-          }
-          try {
-            useContextStore.getState().saveAgentModelVariantForSession(sessionId, agentName, providerID, modelID, variant);
-          } catch {
-            // ignore
-          }
-        }
-      }
-
       const visiblePromptText = await renderMagicPrompt('github.issue.review.visible', {
         issue_number: String(issue.number),
       });
       const instructionsText = await renderMagicPrompt('github.issue.review.instructions');
       const contextText = buildIssueContextText({ repo: issueRes.repo, issue, comments });
 
-      void opencodeClient.sendMessage({
-        id: sessionId,
+      void useSessionUIStore.getState().sendMessage(
+        visiblePromptText,
         providerID,
         modelID,
-        agent: agentName,
-        variant,
-        text: visiblePromptText,
-        additionalParts: [
+        agentName,
+        undefined,
+        undefined,
+        [
           { text: instructionsText, synthetic: true },
           { text: contextText, synthetic: true },
         ],
-        directory: sessionDirectory,
-      }).catch((e) => {
+        variant,
+        undefined,
+        { sessionId },
+      ).catch((e) => {
         const message = e instanceof Error ? e.message : String(e);
         toast.error(t('session.githubIssuePicker.toast.sendContextFailed'), {
           description: message,