refactor(session): make cmd_continue idempotent with ensure_* functions

- Add ensure_worktree() - creates worktree if missing, returns status
- Add ensure_session() - creates session if missing, handles inconsistent states
- Add fork_agent() - extracted agent forking logic
- Refactor cmd_continue() to use ensure_* functions (idempotent)
- Make cmd_start() a thin wrapper calling cmd_continue()
- Simplify daemon to always call cmd_continue (no existence check)

This makes cmd_continue truly idempotent - it will:
- Continue existing session if it exists
- Create session and worktree if they don't exist
- Clean and recreate if state is inconsistent

Closes #168

skills/kugetsu/scripts/kugetsu-session.sh

@@ -270,37 +270,40 @@ build_dev_agent_message() {
     local number=$(echo "$issue_ref" | grep -oE '#[0-9]+$' | tr -d '#')
     local worktree_path=$(issue_ref_to_worktree_path "$issue_ref")
     
-    local conflict_check=""
-    local review_notes=""
-    local delegator_header=""
-    local delegator_footer=""
     if [ -n "$user_message" ]; then
-        conflict_check="   - CRITICAL: Check if PR has merge conflicts before asking for review:
-     - Use: curl -s \"https://$instance/api/v1/repos/$owner/$repo/pulls/$number\" -H \"Authorization: Bearer \$GITEA_TOKEN\"
-     - If \"mergeable\": false, there ARE conflicts - you MUST resolve them FIRST
-     - To resolve: cd to worktree, git fetch origin, git rebase origin/main, resolve conflicts, git rebase --continue, git push --force-with-lease
-     - Only after resolving conflicts (mergeable: true) can you ask for review"
-        delegator_header="IMPORTANT: Follow the workflow below as your guideline, but prioritize the delegator's message.
+        cat <<EOF
+You are continuing work on $issue_ref. A PR likely already exists.
 
-Workflow:"
-        delegator_footer="
+IMPORTANT - Review workflow:
+1. First, check if PR exists: curl -s "https://$instance/api/v1/repos/$owner/$repo/pulls?state=open" -H "Authorization: Bearer \$GITEA_TOKEN" | grep -i "$number"
+2. Get PR comments: curl -s "https://$instance/api/v1/repos/$owner/$repo/issues/$number/comments" -H "Authorization: Bearer \$GITEA_TOKEN"
+3. Get PR reviews: curl -s "https://$instance/api/v1/repos/$owner/$repo/pulls/$number/reviews" -H "Authorization: Bearer \$GITEA_TOKEN"
+
+You may need to:
+- Make code changes and push to the same branch
+- Reply to PR comments using: curl -X POST "https://$instance/api/v1/repos/$owner/$repo/issues/$number/comments" -H "Authorization: Bearer \$GITEA_TOKEN" -H "Content-Type: application/json" -d '{"body":"Your reply here"}'
+- Or do both
+
+MERGING: If instructed to merge, you MUST confirm approval first before merging:
+- Check for PR approval via: curl -s "https://$instance/api/v1/repos/$owner/$repo/pulls/$number/reviews" -H "Authorization: Bearer \$GITEA_TOKEN"
+- Check for "lgtm" or "approved" in comments: curl -s "https://$instance/api/v1/repos/$owner/$repo/issues/$number/comments" -H "Authorization: Bearer \$GITEA_TOKEN"
+- Only merge if you see approval OR the instruction explicitly says to merge (e.g., "merge the PR", "please merge", "go ahead and merge")
+- To merge: tea pr merge --repo $owner/$repo $number --style merge
+- If no approval yet, reply asking for review/approval first
 
 Delegator's message:
-$user_message"
+$user_message
+
+Work directory: $worktree_path (already on the fix branch)
+EOF
     else
-        review_notes="  - IMPORTANT: After listing reviews, READ the review comments and incorporate feedback
-  - Check for review state: \"APPROVED\" means ready to merge, \"COMMENT\" means feedback to address"
-        delegator_header="Workflow:"
-    fi
-    
-    cat <<EOF
+        cat <<EOF
 You are assigned to work on $issue_ref.
 
-$delegator_header
+Workflow:
 1. Read the issue at $instance/$owner/$repo/issues/$number AND all comments on that issue
 2. Check if a PR already exists for this issue
    - If PR exists and is open, review it and learn from it
-$conflict_check
    - If PR makes sense to continue, work on it instead
    - If PR is not worth continuing, create a new branch/PR but explain in PR description why you're creating a new one instead of continuing the existing PR
 3. Read README.md (if exists) to understand the general concept of this repository
@@ -318,14 +321,13 @@ Tools for PR interaction:
 - Post issue/PR comment: curl -X POST "https://$instance/api/v1/repos/$owner/$repo/issues/$number/comments" -H "Authorization: Bearer \$GITEA_TOKEN" -H "Content-Type: application/json" -d '{"body":"Your comment"}'
 - List PR comments: curl -s "https://$instance/api/v1/repos/$owner/$repo/issues/$number/comments" -H "Authorization: Bearer \$GITEA_TOKEN"
 - List PR reviews: curl -s "https://$instance/api/v1/repos/$owner/$repo/pulls/$number/reviews" -H "Authorization: Bearer \$GITEA_TOKEN"
-$review_notes
 - Merge PR (only with approval): tea pr merge --repo $owner/$repo $number --style merge
   - MERGING requires approval first! Check for: approval in reviews, OR "lgtm"/"approved" in comments
   - If no approval, ask reviewer to approve first before merging
-$delegator_footer
 
 Work directory: $worktree_path
 EOF
+    fi
 }
 
 ensure_worktree() {
@@ -384,6 +386,12 @@ ensure_session() {
         return 0
     fi
     
+    if $worktree_exists && ! $session_exists; then
+        log "warn" "ensure_session" "Worktree exists but session is missing. Removing worktree to recreate both..."
+        remove_worktree_for_issue "$issue_ref"
+        worktree_exists=false
+    fi
+    
     if ! $worktree_exists && $session_exists; then
         log "warn" "ensure_session" "Session exists but worktree is missing. Removing stale session..."
         rm -f "$session_path"
@@ -473,8 +481,6 @@ cmd_continue() {
     
     if [ -z "$message" ]; then
         message=$(build_dev_agent_message "$issue_ref" "")
-    else
-        message=$(build_dev_agent_message "$issue_ref" "$message")
     fi
     
     local worktree_status=$(ensure_worktree "$issue_ref")