fix(code-review): revert #178 parallel GitHub fleet → restore synchronous headless dispatch (FEA-3085)

[peterulsteen]

Summary

Reverts #178 (code-review v3.5.0) and bumps 3.4.1 → 3.6.0, restoring synchronous reviewer-fleet dispatch for GitHub/headless mode at stage_20_spawn_reviewers. Local mode keeps parallel background dispatch + blocking TaskOutput.

#178 unified both modes on run_in_background: true + blocking TaskOutput, betting that headless claude -p (Claude Code ≥ v2.1.182) reliably awaits background subagents as long as the orchestrator issues the blocking collection. Empirically it does not: in ~18% of symphony-alpha claude-code-review.yml pull_request runs on 2026-07-13 (9/50, up from 1/10 the day #178 shipped) the orchestrator launched the reviewer fleet (Bug Hunter A/B, Unified Auditor) as background agents and then ended its turn ("I'll wait for the harness to notify me") with no pending synchronous tool call. claude -p then exited (terminal_reason: "completed") before stage_21_collect_findings … stage_30_footer ran — no findings collected, no .closedloop-ai/code-review-* artifacts written, and the workflow's "Validate migrated review artifacts" guard failed the job. Runs that took the synchronous fast-path were unaffected, hence the intermittency.

Synchronous one-at-a-time dispatch (run_in_background: false, wait for each DONE findings=N file=... before the next) keeps the headless turn alive by construction, rather than depending on the model choosing to issue a blocking TaskOutput. This restores the exact pre-#178 state that ran reliably (the verifier fleet at stage_23 was already background+collect in both modes before #178 and is unchanged).

Trade-off: GitHub review wall-clock returns to sum-of-reviewers instead of slowest-reviewer. Correctness over speed for a merge-adjacent gate.

Root-cause detail and the 9 failing run IDs are tracked in FEA-3085.

Feature Flags

N/A — plugin behavior change, no runtime flag.

Breaking changes

None. Restores prior GitHub-mode dispatch semantics; output contract and artifacts unchanged.

Test plan

• uv run --frozen --group dev pytest → 2079 passed, 3 skipped
• ruff check . → clean
• pyright → 0 errors, 0 warnings
• Restored FEA-2162 synchronous-GitHub reviewer test class passes.
• Post-merge: watch symphony-alpha claude-code-review.yml pull_request runs for the artifact-validation failure signature (expect it to clear once CI pulls v3.6.0).

🤖 Generated with Claude Code

[mikeangstadt]

Sound revert. Restores the sync GitHub dispatch that we know keeps the headless turn alive, and the version bump + tests line up. One real question about whether the verifier fleet has the same headless death you're fixing here, plus a changelog nit. Not blocking either.