Improve harness: worktree tracking, completion gate, pwd reporting

- Add pwd/branch reporting at harness start so caller knows the
  working directory
- Add Completion Gate with git status check to prevent uncommitted
  changes from being left behind
- Skill Step 2B reuses existing worktree if PR branch is already
  checked out, instead of always creating a new one
- Step 3 requires main agent to record worktree→PR mapping for
  directing future operations to the correct directory

Signed-off-by: Heng Qian <qianheng@amazon.com>

Author: qianheng-aws

.claude/commands/ppl-bugfix.md

@@ -83,6 +83,33 @@ Agent(
 
 ### 2B: Follow-up
 
+Before dispatching, check if an existing worktree already has the PR branch checked out:
+
+```bash
+# List worktrees and find one on the PR branch
+for wt in .claude/worktrees/agent-*/; do
+  branch=$(git -C "$wt" branch --show-current 2>/dev/null)
+  if [ "$branch" = "<pr_branch>" ]; then
+    echo "REUSE: $wt (branch: $branch)"
+  fi
+done
+```
+
+**If existing worktree found**: Do NOT use `isolation: "worktree"`. Pass the worktree path in the prompt so the subagent works there directly.
+
+```
+Agent(
+  mode: "<resolved_mode>",
+  name: "bugfix-<issue_number>",
+  description: "PPL bugfix #<issue_number> followup",
+  prompt: "cd <worktree_path> first, then read .claude/harness/ppl-bugfix-followup.md and follow it.
+           PR: <pr_number> (<pr_url>), Issue: #<issue_number>
+           Working directory: <worktree_path>"
+)
+```
+
+**If no existing worktree**: Create a new one.
+
 ```
 Agent(
   mode: "<resolved_mode>",
@@ -100,6 +127,16 @@ After all subagents complete, report a summary for each:
 - Classification, fix summary, PR URL, worktree path and branch, items needing human attention (2A)
 - What was addressed, current PR state, whether another round is needed (2B)
 
+**Always include the worktree→PR mapping** from the subagent's output, e.g.:
+
+```
+Worktree: /path/to/.claude/worktrees/agent-xxxx
+Branch: bugfix-1234
+PR: #5678
+```
+
+**Important**: After reporting, the main agent must remember this mapping. When the user later asks to make changes to the PR (e.g., "commit this to PR #5678"), operate in the worktree directory — not the main session directory.
+
 ## Subagent Lifecycle
 
 Subagents are task-scoped. They complete and release context — they cannot poll for events.

.claude/harness/ppl-bugfix-followup.md

@@ -6,9 +6,18 @@
 
 ---
 
+## Report Working Directory
+
+```bash
+echo "Worktree: $(pwd)"
+echo "Branch: $(git branch --show-current)"
+```
+
+Include this in your output so the caller knows where changes are happening.
+
 ## Reconstruct Context
 
-The follow-up agent runs in a fresh worktree. First checkout the PR branch, then load state:
+First checkout the PR branch, then load state:
 
 ```bash
 # Checkout the PR branch in this worktree
@@ -101,3 +110,16 @@ For each comment addressed (bot or human):
 - **Did the follow-up workflow itself miss this signal?** → Update this file
 
 If any improvement is needed, make the edit and include it in the same commit.
+
+## Completion Gate
+
+Before reporting "done":
+
+1. Run `git status --porcelain` — if any uncommitted changes remain, commit and push them. This includes harness edits from Retrospective.
+2. Report in your final output:
+
+```
+Worktree: <absolute path>
+Branch: <branch name>
+PR: <pr_number>
+```

.claude/harness/ppl-bugfix-harness.md

@@ -2,6 +2,15 @@
 
 ## Phase 0: Triage
 
+### 0.0 Report Working Directory
+
+```bash
+echo "Worktree: $(pwd)"
+echo "Branch: $(git branch --show-current)"
+```
+
+Include this in your output so the caller knows where changes are happening.
+
 ### 0.1 Load & Reproduce
 
 ```bash
@@ -126,6 +135,8 @@ EOF
 
 ## Completion Gate
 
+Run `git status --porcelain` — if any uncommitted changes remain, commit and push them before proceeding.
+
 Do NOT report "done" until every item below is checked. List each in your final report:
 
 - [ ] **Unit tests**: New test class or methods
@@ -149,3 +160,10 @@ If any item is blocked, report which and why.
 - [ ] New pattern? Add to Case Index.
 
 Include harness improvements in the same PR.
+
+Report in your final output:
+```
+Worktree: <absolute path>
+Branch: <branch name>
+PR: <pr_number>
+```