feat(#143): fetch doc-map config from trusted VCS ref

The doc-map YAML config was previously read from the local workspace
(the PR branch checkout). A malicious PR author could modify
.review-bot/doc-map.yml to map any path glob to sensitive design docs,
causing review-bot to fetch and inject those docs into the LLM prompt.

Fix: add --doc-map-trusted-ref (DOC_MAP_TRUSTED_REF) flag. When set to
a trusted ref (e.g. 'main'), the doc-map config is fetched from the VCS
API at that ref instead of from local workspace. A 404 from VCS is a
hard error (no silent fallback to local copy).

When unset, the local workspace is used with a security warning in the
logs pointing operators to the new flag.

Changes:
- review/docmap.go: add ParseDocMapConfigContent + parseDocMapBytes
  helper to parse from in-memory content (fetched via VCS API)
- cmd/review-bot/main.go: add --doc-map-trusted-ref flag; Step 6c
  branches on trusted-ref to fetch vs local-workspace load
- .gitea/actions/review/action.yml: add doc-map-trusted-ref input
- README.md: document new input
- CHANGELOG.md: security and feature entries

Tests:
- TestParseDocMapConfigContent_Valid/Empty/InvalidYAML/UnknownKeys
  in review/docmap_test.go

Coverage: 53.0% cmd/review-bot

.gitea/actions/review/action.yml

@@ -141,6 +141,16 @@ inputs:
     description: 'Maximum bytes of injected doc content from doc-map (default 102400 = 100KB)'
     required: false
     default: '102400'
+  doc-map-trusted-ref:
+    description: >-
+      Git ref (branch, tag, or SHA) from which to fetch the doc-map config file
+      via VCS API instead of reading it from the local workspace. Recommended
+      when using doc-map: set this to the default branch (e.g. 'main') so a
+      malicious PR cannot modify the doc-map config to inject arbitrary design
+      docs into the LLM prompt. When unset, the config is read from the local
+      workspace (the PR branch) with a security warning in the logs.
+    required: false
+    default: ''
 
 runs:
   using: 'composite'
@@ -506,6 +516,7 @@ runs:
         PERSONA_FILE: ${{ inputs.persona-file }}
         DOC_MAP_FILE: ${{ inputs.doc-map }}
         DOC_MAP_MAX_BYTES: ${{ inputs.doc-map-max-bytes }}
+        DOC_MAP_TRUSTED_REF: ${{ inputs.doc-map-trusted-ref }}
         AICORE_CLIENT_ID: ${{ inputs.aicore-client-id }}
         AICORE_CLIENT_SECRET: ${{ inputs.aicore-client-secret }}
         AICORE_AUTH_URL: ${{ inputs.aicore-auth-url }}

CHANGELOG.md

@@ -2,8 +2,14 @@
 
 ## Unreleased
 
+### Security
+
+- **`doc-map-trusted-ref`: fetch doc-map config from trusted VCS ref** ([#143](https://gitea.weiker.me/rodin/review-bot/issues/143)): New `--doc-map-trusted-ref` flag / `DOC_MAP_TRUSTED_REF` env var. When set, the doc-map YAML config is fetched from the specified VCS ref (e.g. `main`) via API instead of being read from the local workspace (the PR branch checkout). This prevents a malicious PR from modifying `.review-bot/doc-map.yml` to inject arbitrary design docs into the LLM prompt. When unset, the local workspace is used with a security warning in the logs.
+
 ### Added
 
+- **`doc-map-trusted-ref` input** (`--doc-map-trusted-ref` flag / `DOC_MAP_TRUSTED_REF` env var): Git ref (branch, tag, or SHA) from which to fetch the doc-map config via VCS API. Recommended for all `doc-map` users. Example: `doc-map-trusted-ref: main`. ([#143](https://gitea.weiker.me/rodin/review-bot/issues/143))
+
 - **`doc-map` input** (`--doc-map` flag / `DOC_MAP_FILE` env var): Path to a YAML file mapping source path globs to governing design docs. review-bot intersects the map with changed PR paths and injects matching docs into the system prompt under a `## Design Documents` heading. ([#137](https://gitea.weiker.me/rodin/review-bot/issues/137))
 - **`doc-map-max-bytes` input** (`--doc-map-max-bytes` flag / `DOC_MAP_MAX_BYTES` env var): Cap on total injected design doc content in bytes. Default: 102400 (100 KB). Prevents accidental context overflow when a PR touches many modules.
 - **`DesignDocs` budget section**: Design docs are included in the context budget and trimmed after conventions, before file context, if the total exceeds the model's context limit.

README.md

@@ -210,6 +210,7 @@ AI Core handles OAuth token management and deployment discovery automatically. M
 | `system-prompt-file` | No | `""` | Local file with additional system prompt instructions |
 | `doc-map` | No | `""` | Path to a YAML file mapping source path globs to governing design docs |
 | `doc-map-max-bytes` | No | `102400` | Maximum bytes of injected doc content from doc-map (default 100KB) |
+| `doc-map-trusted-ref` | No | `""` | Git ref (e.g. `main`) to fetch the doc-map config from via VCS API instead of local workspace. **Recommended for security** — prevents a PR from modifying the doc-map config to inject arbitrary docs. |
 | `persona` | No | `""` | Built-in persona name (security, architect, docs) |
 | `persona-file` | No | `""` | Path to persona file (YAML or JSON) with custom review focus |
 | `temperature` | No | `0` | LLM temperature (0 = server default) |

cmd/review-bot/main.go

@@ -101,6 +101,7 @@ func main() {
 	aicoreResourceGroup := flag.String("aicore-resource-group", envOrDefault("AICORE_RESOURCE_GROUP", "default"), "SAP AI Core resource group (for provider=aicore)")
 	docMapFile := flag.String("doc-map", envOrDefault("DOC_MAP_FILE", ""), "Path to YAML file mapping source path globs to governing design docs")
 	docMapMaxBytes := flag.Int("doc-map-max-bytes", envOrDefaultInt("DOC_MAP_MAX_BYTES", review.DefaultDocMapMaxBytes), "Maximum bytes of injected doc content (default 102400)")
+	docMapTrustedRef := flag.String("doc-map-trusted-ref", envOrDefault("DOC_MAP_TRUSTED_REF", ""), "Git ref (e.g. main) to fetch the doc-map config from via VCS API instead of local workspace. Recommended to prevent PR branch from controlling which docs are injected.")
 
 	flag.Parse()
 
@@ -368,10 +369,45 @@ func main() {
 	// Step 6c: Load path-scoped design docs if doc-map specified
 	designDocs := ""
 	if *docMapFile != "" {
-		docMapCfg, err := review.ParseDocMapConfig(resolvedDocMapFile)
-		if err != nil {
-			slog.Error("failed to parse doc-map file", "file", *docMapFile, "error", err)
-			os.Exit(1)
+		var docMapCfg *review.DocMapConfig
+
+		if *docMapTrustedRef != "" {
+			// Fetch doc-map config from a trusted VCS ref (e.g. the default branch).
+			// This prevents a malicious PR from modifying the doc-map config to
+			// inject arbitrary docs into the LLM prompt.
+			slog.Info("doc-map: fetching config from trusted ref",
+				"path", *docMapFile,
+				"ref", *docMapTrustedRef)
+			content, fetchErr := vcs.GetFileContentRef(ctx, owner, repoName, *docMapFile, *docMapTrustedRef)
+			if fetchErr != nil {
+				slog.Error("doc-map: failed to fetch config from trusted ref",
+					"path", *docMapFile,
+					"ref", *docMapTrustedRef,
+					"error", fetchErr)
+				os.Exit(1)
+			}
+			source := fmt.Sprintf("%s/%s@%s:%s", owner, repoName, *docMapTrustedRef, *docMapFile)
+			var parseErr error
+			docMapCfg, parseErr = review.ParseDocMapConfigContent(content, source)
+			if parseErr != nil {
+				slog.Error("doc-map: failed to parse fetched config",
+					"source", source,
+					"error", parseErr)
+				os.Exit(1)
+			}
+		} else {
+			// Local workspace fallback — the doc-map is read from the PR branch checkout.
+			// SECURITY WARNING: a malicious PR can modify this file to inject arbitrary
+			// docs. Set --doc-map-trusted-ref (or DOC_MAP_TRUSTED_REF) to a trusted ref
+			// (e.g. "main") to fetch the config from the default branch instead.
+			slog.Warn("doc-map: loading config from local workspace (PR branch) — " +
+				"set --doc-map-trusted-ref to fetch from a trusted ref for security")
+			var parseErr error
+			docMapCfg, parseErr = review.ParseDocMapConfig(resolvedDocMapFile)
+			if parseErr != nil {
+				slog.Error("failed to parse doc-map file", "file", *docMapFile, "error", parseErr)
+				os.Exit(1)
+			}
 		}
 
 		// Collect changed file paths from the PR for intersection.
@@ -385,10 +421,11 @@ func main() {
 
 		if len(matchedDocs) > 0 {
 			docMapOpts := review.DocMapOptions{MaxBytes: *docMapMaxBytes}
-			designDocs, err = review.LoadMatchingDocs(ctx, vcs, owner, repoName, matchedDocs, docMapOpts)
-			if err != nil {
+			var loadErr error
+			designDocs, loadErr = review.LoadMatchingDocs(ctx, vcs, owner, repoName, matchedDocs, docMapOpts)
+			if loadErr != nil {
 				// Non-fatal: individual missing files are already warned; log and continue.
-				slog.Warn("doc-map: partial failure loading docs", "error", err)
+				slog.Warn("doc-map: partial failure loading docs", "error", loadErr)
 			}
 			if designDocs != "" {
 				slog.Info("doc-map: injected design docs", "matched", len(matchedDocs), "bytes", len(designDocs))

review/docmap.go

@@ -52,15 +52,31 @@ func ParseDocMapConfig(localPath string) (*DocMapConfig, error) {
 	if err != nil {
 		return nil, fmt.Errorf("read doc-map file %q: %w", localPath, err)
 	}
+	return parseDocMapBytes(data, localPath)
+}
 
+// ParseDocMapConfigContent parses a doc-map YAML config from an in-memory
+// string. The source parameter is used only for error messages and log entries
+// (e.g. "main:main@<ref>").
+//
+// Use this when the config content has been fetched from a trusted VCS ref
+// rather than read from the local workspace.
+func ParseDocMapConfigContent(content, source string) (*DocMapConfig, error) {
+	data := []byte(content)
+	return parseDocMapBytes(data, source)
+}
+
+// parseDocMapBytes is the shared YAML parse implementation used by
+// ParseDocMapConfig and ParseDocMapConfigContent.
+func parseDocMapBytes(data []byte, source string) (*DocMapConfig, error) {
 	var cfg DocMapConfig
 	if err := yaml.UnmarshalWithOptions(data, &cfg, yaml.Strict()); err != nil {
 		// Re-parse without strict mode to log which keys are unknown.
 		var relaxed DocMapConfig
 		if err2 := yaml.Unmarshal(data, &relaxed); err2 != nil {
-			return nil, fmt.Errorf("parse doc-map YAML %q: %w", localPath, err)
+			return nil, fmt.Errorf("parse doc-map YAML %q: %w", source, err)
 		}
-		slog.Warn("doc-map YAML contains unknown keys (ignored)", "file", localPath, "error", err)
+		slog.Warn("doc-map YAML contains unknown keys (ignored)", "file", source, "error", err)
 		cfg = relaxed
 	}
 	return &cfg, nil

review/docmap_test.go

@@ -510,3 +510,63 @@ func TestFileCoveredByDocMap_EmptyConfig(t *testing.T) {
 		t.Error("expected false for empty config, got true")
 	}
 }
+
+// ============================================================
+// ParseDocMapConfigContent
+// ============================================================
+
+func TestParseDocMapConfigContent_Valid(t *testing.T) {
+	content := `
+mappings:
+  - paths:
+      - "lib/foo/**"
+    docs:
+      - docs/foo.md
+`
+	cfg, err := ParseDocMapConfigContent(content, "owner/repo@main:.review-bot/doc-map.yml")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if len(cfg.Mappings) != 1 {
+		t.Fatalf("expected 1 mapping, got %d", len(cfg.Mappings))
+	}
+	if len(cfg.Mappings[0].Docs) != 1 || cfg.Mappings[0].Docs[0] != "docs/foo.md" {
+		t.Errorf("unexpected mapping: %+v", cfg.Mappings[0])
+	}
+}
+
+func TestParseDocMapConfigContent_EmptyContent(t *testing.T) {
+	cfg, err := ParseDocMapConfigContent("", "test-source")
+	if err != nil {
+		t.Fatalf("unexpected error for empty content: %v", err)
+	}
+	if len(cfg.Mappings) != 0 {
+		t.Errorf("expected 0 mappings for empty content, got %d", len(cfg.Mappings))
+	}
+}
+
+func TestParseDocMapConfigContent_InvalidYAML(t *testing.T) {
+	_, err := ParseDocMapConfigContent("mappings: [{{invalid", "test-source")
+	if err == nil {
+		t.Fatal("expected error for invalid YAML, got nil")
+	}
+}
+
+func TestParseDocMapConfigContent_UnknownKeys(t *testing.T) {
+	content := `
+mappings:
+  - paths:
+      - "lib/**"
+    docs:
+      - docs/foo.md
+unknown_top_level_key: "should be warned but not fatal"
+`
+	// Unknown top-level keys produce a warning but not an error.
+	cfg, err := ParseDocMapConfigContent(content, "test-source")
+	if err != nil {
+		t.Fatalf("unexpected error for unknown keys: %v", err)
+	}
+	if len(cfg.Mappings) == 0 {
+		t.Error("expected mappings to be parsed despite unknown key")
+	}
+}