docs: rework design after prior-art review

Red Hat's MIT ai-code-review already implements phases 1-2 (four forge clients,
six providers, CI integration, repo context file). Adds a research writeup,
inserts Phase 0 (evaluate it before building), and folds in seven requirements
the original design missed — chiefly prior-comment synthesis, without which our
own 1.7-runs-per-PR assumption means every push re-posts dismissed findings.

Amends implementation tasks 4, 5, 6, 9, 10 and gates the subagent briefs.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011Ye1KNFMkkUtmzTypHXkoK

docs/plans/2026-08-04-pragent-implementation.md

@@ -12,6 +12,73 @@
 
 ---
 
+## ⚠️ Read this before dispatching Task 1
+
+A prior-art review on 2026-08-04 found Red Hat's MIT-licensed `ai-code-review`
+(https://gitlab.com/redhat/edge/ci-cd/ai-code-review) already implements Phases 1–2 of
+this design: four forge clients, six AI providers, CI integration, a committed
+repo-context file. **Phase 0 of the design is now "evaluate that tool for a week."**
+See `docs/research/2026-08-04-prior-art-ai-code-review.md`.
+
+Do not start Task 1 until Phase 0 concludes we are building standalone. If it concludes we
+extend an existing base instead, most of the tasks below become unnecessary and the
+project starts at the tier engine, analyzer bus, and analytics layer.
+
+The amendments in the next section apply **whichever** path we take.
+
+## Amendments (2026-08-04, post prior-art review)
+
+Apply these on top of the task steps below. Where an amendment conflicts with the original
+task text, the amendment wins.
+
+**Task 4 (tier engine)** — add deterministic skip conditions before the path and size
+rules, since they are free and catch cases the original rules miss:
+
+- `ReviewContext` gains `isDraft: boolean`, `authorIsBot: boolean`, `commitSubject: string`,
+  `branch: string`, `labels: string[]`.
+- `classify()` takes the context, not just the file list. New rules, highest precedence:
+  draft MR → `trivial` / `rule:draft`; `/^\s*(wip|draft)\b/i` on the commit subject →
+  `rule:wip_commit`; `wip/` branch prefix → `rule:wip_branch`; bot author →
+  `rule:bot_author`; a configured skip label → `rule:skip_label(<name>)`.
+- Tests: one per rule, plus one asserting a **risk-path change in a draft MR still skips** —
+  decide that deliberately and encode it (a draft is explicitly not ready for review; the
+  risk path will be caught when it opens).
+
+**Task 5 (config)** — add keys: `skipLabels: string[]` (default `["skip-review"]`),
+`maxChars: number` (provider-aware default, 150000 for Anthropic), `maxFiles: number`
+(default 100), `excludePatterns: string[]` (lockfiles, minified, `dist/**`, `node_modules/**`,
+`__pycache__/**`), `teamContextFile: string | null`, `dryRun: boolean`. Environment
+variables become a config layer between the file and CLI flags: **CLI > env > file >
+defaults** — CI systems supply secrets and URLs by environment, and the original design
+had no way to receive them.
+
+**Task 6 (analyzer runner)** — the prompt builder takes an optional `priorContext: string`
+and, when present, includes it under a heading instructing the model not to repeat points
+already made or explicitly rejected. Phase 1 always passes `undefined`; Phase 2 fills it.
+Adding the parameter now costs one line and avoids reshaping the prompt module later.
+
+**Task 6 (input clamp)** — before building the prompt, truncate the joined diff at
+`config.maxChars` and drop files matching `excludePatterns`. When truncation happens, say
+so in the prompt (`[diff truncated at N characters]`) rather than silently sending a
+partial diff, and record it on the run record.
+
+**Task 9 (run record)** — add `skipped: boolean`, `truncated: boolean`, and
+`synthesis_cost_usd: number` (0 in Phase 1) to `RunRecord` and `toWireFormat`. Adding
+fields later means old JSONL lines lack them, which breaks the analytics queries that are
+the point of the format.
+
+**Task 10 (CLI)** — add `--dry-run`, which uses a mock `ModelClient` returning a fixed
+finding. This lets a team wire up the pipeline and verify plumbing before an API key
+exists, and it makes the end-to-end test runnable in CI without network access.
+
+**New Phase 2 task (not in this plan) — review-context synthesis.** Fetch all prior
+comments including resolved ones, compress with a Haiku-class model, pass the result to
+analyzers as `priorContext`. This is the highest-value item in the whole backlog: without
+it, our own 1.7-runs-per-PR cost assumption means every push re-posts findings a human
+already dismissed. Plan it before Phase 2's Gitea adapter work is considered done.
+
+---
+
 ## Ground rules for the implementer
 
 - **TDD, strictly.** Write the failing test, watch it fail, write the minimum code, watch it pass, commit. A step that says "run it and see it fail" is not decoration — a test that passes before the implementation exists is a broken test.