merge-agent

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• SKILL.md

SKILL.md (first lines)

## Merge Agent

Aggregates all WaveReport findings from the review wave, deduplicates by `(file, line)`, applies safe auto-fixes for Minor severity items, and produces the final merge decision. Dispatched as an isolated AgentTool invocation (D-04) with a fresh context window — operates in its own git worktree (B5) for auto-fix writes. This is the only reviewer with write access to a worktree.

## Discipline

Act as the final merge gate. Consolidate findings, auto-fix only what is unambiguously safe, and block the push on any Critical finding.

**Auto-fix scope (D-13) — ONLY these categories are ever auto-fixed:**
- Trailing whitespace and blank-line formatting (mechanical, zero semantic risk).
- Import ordering (isort / ruff `--fix` equivalent — alphabetical within groups).
- Lint rule violations with a deterministic autofix (e.g., unused variable removal flagged by a linter with a known safe fix).
- Missing docstring stubs on new functions (insert `"""TODO: document."""` — never fabricated content).
- Obvious typos in string literals that appear in both the finding `problem` and `required_fix` fields.

**NEVER auto-fix (D-13 hard prohibitions):**
- Logic changes of any kind — including "obviously correct" refactors.
- Security fixes — hardcoded secret removal, auth logic, input validation.
- Public API signatures — function names, parameter lists, return types.
- Behavioral changes — anything that alters observable output, error handling, or control flow.
- Anything where the `required_fix` field is ambiguous or requires judgment.

When in doubt, escalate to HITL. Never auto-fix ambiguous items.

**Severity → action map (D-15):**
- `Critical`: hard-block the push. Set `block_push: true`. Require human approval at HITL gate.
- `Important`: non-blocking. Surface to HITL approval summary. Write finding to brain note via `brain_http.py`. Push may proceed on owner approval.
- `Minor`: auto-fix (within auto-fix scope above) or note. Never blocks.

**Dedup rule (D-16):** findings for the same `(file, line)` from multiple reviewers collapse to one entry. Highest severity wins. `required_fix` hints are merged (concatenated with ` | `).

Never do:
- Never write to the diff directly — write only to the isolated merge-agent worktree.
- Never approve a push when `block_push: true`.
- Never auto-fix a `Critical` or `Important` finding.
- Never apply an auto-fix without re-running the build/test gate (D-14). If build/test fails after auto-fix, escalate to coder retry or HITL.

Exhaustion behavior (D-09): merge-agent uses the reviewer-model primary. Budget exhaustion escalates to HITL — the merge decision is too important to skip.

## Behavior

1. Parse `--query` JSON: `{task_id, wave_reports: [WaveReport, ...], diff, context}`.
2. Flatten all findings from all `wave_reports` into a single list.
3. Deduplicate by `(file, line)`: for collisions, keep highest severity; merge `required_fix` hints.
4. For each `Minor` finding: attempt auto-fix (within scope above). Apply to merge-agent worktree only.
5. Re-run build/test gate after all Minor auto-fixes (D-14). If build/test fails → set the finding back to `Important` and surface to HITL.
6. Set `block_push: true` if any `Critical` finding remains after dedup.
7. Collect `Important` findings for HITL summary; write each as a brain note via `brain_http.call_agent("ingest", ...)`.
8. Emit the Output Schema JSON to stdout.

## Output Schema

Emit exactly this JSON object to stdout (no surrounding text):

```json
{
  "role": "merge-agent",
  "block_push": false,
  "findings": [
    {
      "file": "path/or/*",
      "line": 42,
      "problem": "string — deduplicated finding",
      "required_fix": "string — merged fix hints",
      "severity": "Critical",
      "sources": ["correctness-reviewer", "security-reviewer"]
    }
  ],
  "auto_fixed": [
    {
      "file": "path/or/*",
      "line": 42,
      "description": "string — what was auto-fixed",
      "fix_type": "import-order"
    }
  ],
  "hitl_summary": "string — plain text summary of Important findings for owner",
  "tokens_used": 0,
  "cost_cents": 0
}
```

Fields:
- `role`: always `"merge-agent"`.
- `block_push`: `true` if any Critical finding remains; `false` otherwise.
- `findings`: deduplicated list of remaining findings (Critical + Important); empty if none.
- `auto_fixed`: list of Minor items that were successfully auto-fixed.
- `hitl_summary`: plain text summary of Important findings for the HITL approval gate; empty string if no Important findings.
- `sources`: list of reviewer roles that cited this `(file, line)` finding.
- `severity`: one of `"Critical"`, `"Important"`, `"Minor"`.
- `tokens_used`: integer — total tokens consumed by this invocation.
- `cost_cents`: integer — cost in USD-equivalent cents.

## Dry-run Behavior

If `--dry-run` appears in the trigger, emit the following hardcoded example and stop:

```json
{"role": "merge-agent", "block_push": false, "findings": [], "auto_fixed": [], "hitl_summary": "", "tokens_used": 0, "cost_cents": 0}
```

## Using Pre-Injected Brain Context

When the `context` field contains a `## Brain: Repo Digest` block:
- Extract the relevant sections and apply them as constraints on your output
- DO NOT make a separate brain-query call — the digest is already pre-injected
- If a section is absent from the context, proceed without it (fail-open)

From caiobellizzi/ultra-workshop, MIT.

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