ci: Stop using subagents in claude-review workflow

As it seems impossible to prevent claude from receiving notifications
about subagents finishing after it has produced structured output, which
breaks the structured output as it has to be the final reply, let's stop
using subagents and background tasks completely to avoid the issue.

.github/workflows/claude-review.yml

@@ -250,10 +250,14 @@ jobs:
                 "allowUnsandboxedCommands": false
               }
             }
+          # Agent and TaskCreate are disabled because background task
+          # notifications race with --json-schema structured output,
+          # causing a redundant turn that overwrites the result.
+          # See https://github.com/anthropics/claude-code/issues/33872
           claude_args: |
             --model us.anthropic.claude-opus-4-6-v1
             --max-turns 200
-            --disallowedTools "WebFetch,WebSearch"
+            --disallowedTools "WebFetch,WebSearch,Agent,TaskCreate"
             --json-schema '${{ env.REVIEW_SCHEMA }}'
           prompt: |
               REPO: ${{ github.repository }}
@@ -263,7 +267,8 @@ jobs:
               produce a structured JSON result containing your review. Do NOT attempt
               to post comments yourself — just return the JSON. You are in the upstream repo
               with the PR branch available as `pr-review`. Do not apply or merge the patch.
-              You have no network access — all required context has been pre-fetched locally.
+              You have no network access — all required context has been pre-fetched
+              locally. You cannot spawn subagents or background tasks.
 
               ## Phase 1: Read context
 
@@ -281,16 +286,15 @@ jobs:
               `git log --reverse --format=%H HEAD..pr-review` to list the PR commits, and
               `git show <sha>` or `git diff <sha>~1..<sha>` to access commit diffs.
 
-              ## Phase 2: Per-commit review with subagents
+              ## Phase 2: Per-commit review
 
-              Launch a subagent for each commit in the PR, all in parallel. Each subagent
-              receives only the commit SHA to review. It reads `pr-context.json` for PR
-              context, uses `git show <sha>` or `git diff <sha>~1..<sha>` to fetch the
-              diff, and reads the codebase to verify its findings.
+              Review each commit in the PR sequentially. For each commit, use
+              `git show <sha>` or `git diff <sha>~1..<sha>` to fetch the diff,
+              and read relevant source files in the codebase to verify findings.
 
-              Each subagent reviews code quality, style, potential bugs, and security
-              implications. It must return a JSON array:
-              `[{"file": "path", "line": <number> (optional), "severity": "must-fix|suggestion|nit", "body": "...", "commit": "<sha>"}]`
+              For each commit, review code quality, style, potential bugs, and
+              security implications. Collect issues in the format:
+              `{"file": "path", "line": <number> (optional), "severity": "must-fix|suggestion|nit", "body": "...", "commit": "<sha>"}`
 
               The `commit` field MUST be the SHA of the commit being reviewed. Only
               comment on changes in that commit — not preceding commits.
@@ -299,7 +303,7 @@ jobs:
               inside a diff hunk**. GitHub rejects lines outside the diff context. If you
               cannot determine a valid diff line, omit `line`.
 
-              Each subagent MUST verify findings before returning them:
+              You MUST verify findings before including them:
               - For style/convention claims, check at least 3 existing examples in the
                 codebase to confirm the pattern actually exists before flagging a violation.
               - For "use X instead of Y" suggestions, confirm X actually exists and works.
@@ -307,11 +311,7 @@ jobs:
 
               ## Phase 3: Collect, deduplicate, and summarize
 
-              Wait for all commit review subagents to complete. Monitor your
-              remaining turns — if you are running low (fewer than 20 turns
-              left), immediately stop all still-running subagents using
-              TaskStop and proceed with whatever results you have so far. A
-              partial review is better than no review. Then:
+              After reviewing all commits:
               1. Collect all issues. Merge duplicates (same file, lines within 3 of each other, same problem).
               2. Drop low-confidence findings.
               3. Check the existing inline review comments fetched in Phase 1. Do NOT include a
@@ -374,13 +374,6 @@ jobs:
 
               ## CRITICAL: Return structured JSON output
 
-              Before returning structured output, stop ALL running background tasks
-              using TaskStop and wait for each one to fully terminate. Do NOT
-              return structured output while any background task is still
-              running — a background task completing after you return will
-              trigger a new conversation turn that overwrites your result and
-              causes the workflow to fail.
-
               Your FINAL action must be to return a JSON object matching the following
               JSON schema — do NOT end with a text summary or narrative. The `--json-schema`
               flag is set, so your last response must be the structured JSON result, not a