chore: dev-loop run 2026-05-15 09:15 UTC — all branches passing, ready for review

PLAN-143.md

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+# PLAN-143: Load doc-map config from trusted (default) branch
+
+**Issue:** #143  
+**Status:** Planning  
+**Branch:** TBD (issue-143)
+
+---
+
+## Problem Statement
+
+The `--doc-map` flag reads the doc-map YAML config from the local `GITHUB_WORKSPACE` checkout, which is the **PR branch** in CI. A malicious PR author can:
+
+1. Modify `.review-bot/doc-map.yml` in their branch to map any path glob to sensitive docs  
+2. review-bot reads the PR-branch doc-map config  
+3. Docs from the **default branch** are fetched and injected into the LLM prompt  
+4. Via prompt injection in those docs, the attacker could exfiltrate content  
+
+The config is the trust boundary. The *data* fetched (design docs) already comes from the default branch via VCS API. The *config* is what needs to be pinned to the default branch.
+
+## Constraints
+
+- Must not break existing callers (backward compatibility)
+- Should have a clearly named flag/env var
+- Fall back to local workspace if no trusted ref configured (for users not yet migrated)
+- The gargoyle workflow (.github/workflows/review.yml) will need updating
+
+## Proposed Approach
+
+### Option A: Fetch via VCS API from default branch (preferred)
+
+Add a new flag `--doc-map-trusted-ref` (default: `""` = use local workspace).
+
+When `--doc-map-trusted-ref` is set:
+1. Use the VCS API to fetch the file at `--doc-map` path from the specified ref  
+2. Parse the fetched content as YAML  
+3. Use this config (not the local workspace copy)
+
+When `--doc-map-trusted-ref` is empty:
+- Current behavior (local workspace) with a deprecation warning
+
+This follows the same pattern as `patterns-repo` which fetches from VCS.
+
+### Option B: Auto-detect and always use default branch
+
+Always fetch doc-map from the default branch via VCS API, ignoring local workspace.
+Simpler API but breaks local testing (where there's no VCS to fetch from).
+
+### Recommendation
+
+Option A — explicit `--doc-map-trusted-ref` flag. The gargoyle workflow would set:
+```yaml
+doc-map-trusted-ref: "main"
+```
+
+This is explicit and allows local testing to continue using local workspace.
+
+## Implementation Plan
+
+### Phase 1: VCS API fetch for doc-map config
+
+**Files to change:**
+- `cmd/review-bot/main.go` — add `--doc-map-trusted-ref` flag, conditional fetch logic
+- `review/docmap.go` — add `FetchDocMapConfig(vcs, owner, repo, ref, path string) (*DocMapConfig, error)`
+- `action.yml` — add `doc-map-trusted-ref` input
+- `README.md` — document new flag
+
+**Logic:**
+```go
+if *docMapTrustedRef != "" {
+    // Fetch from VCS (trusted branch) — secure
+    content, err := vcs.GetFileContent(ctx, owner, repoName, *docMapTrustedRef, resolvedDocMap)
+    ...
+    docMapCfg, err = review.ParseDocMapConfigContent(content)
+} else {
+    // Local workspace (backward compat with deprecation warning)
+    slog.Warn("doc-map loaded from local workspace (PR branch) — consider --doc-map-trusted-ref for security")
+    docMapCfg, err = review.ParseDocMapConfig(resolvedDocMap)
+}
+```
+
+### Phase 2: Tests
+
+- `TestFetchDocMapConfig_Success`: mock VCS returns valid YAML → parses correctly
+- `TestFetchDocMapConfig_NotFound`: VCS returns 404 → clear error
+- `TestMainSubprocess_DocMapTrustedRef`: subprocess test for the new flag
+
+### Phase 3: Gargoyle workflow update
+
+Update `.github/workflows/review.yml` in gargoyle to add `doc-map-trusted-ref: main`.
+
+## State/Data Model
+
+New flag: `--doc-map-trusted-ref` / `DOC_MAP_TRUSTED_REF` env var  
+- Type: string  
+- Default: `""` (local workspace)  
+- Example value: `"main"`, `"master"`, `HEAD`  
+
+## Error Cases
+
+- VCS returns 404 for doc-map path at trusted ref → error + exit (not silent)
+- VCS returns 404 but local copy exists → do NOT fall back (could be attack path)
+- Parse error on fetched content → error + exit
+
+## Edge Cases
+
+- What if the doc-map doesn't exist at the trusted ref? → log error, exit (don't silently continue)
+- What if trusted-ref is a commit SHA? → should work via VCS GetFileContent
+- What if the user sets trusted-ref to the PR branch? → Works, but defeats the purpose. Not our problem to prevent.
+
+## Open Questions
+
+- Should we warn when `--doc-map` is set without `--doc-map-trusted-ref`? → Yes, deprecation warning pointing to docs
+- Should we add `--doc-map-trusted-ref` to the `validate-docmap` subcommand? → No, that subcommand operates on local files only; it's a developer tool
+
+## Acceptance Criteria
+
+- [ ] `--doc-map-trusted-ref` flag added to `action.yml` and `cmd/review-bot/main.go`
+- [ ] When set, doc-map config fetched from VCS at the specified ref (not local workspace)
+- [ ] When unset, local workspace used with deprecation warning in logs
+- [ ] 404 from VCS is a hard error (no silent fallback to local copy)
+- [ ] Tests cover: fetch success, fetch 404, parse error
+- [ ] Gargoyle `.github/workflows/review.yml` updated to use `doc-map-trusted-ref: main`
+- [ ] README updated
+- [ ] CHANGELOG updated
+- [ ] `make precommit` passes