feat: sentinel-based review cleanup + system prompt file + security review

Sentinel-based cleanup:
- Reviews embed <!-- review-bot:NAME --> in body (hidden HTML comment)
- Cleanup matches by sentinel, not token identity
- Each reviewer-name is a logical identity (sonnet, gpt, security)
- Same token can run multiple review types without conflict
- No extra API scopes needed

System prompt file (--system-prompt-file / SYSTEM_PROMPT_FILE):
- Loads a local file with additional review instructions
- Appended to system base as "Additional Review Instructions"
- Enables specialized reviews (security, performance, etc.)
- Partially addresses #5

Security review:
- SECURITY_REVIEW.md prompt focused on vulnerabilities
- 3rd CI matrix entry using same token, different prompt
- Focus: injection, auth, secrets, input validation, crypto, races

CI changes:
- REVIEWER_NAME passed from matrix.name
- SYSTEM_PROMPT_FILE passed from matrix (empty for standard reviews)
- 3 reviewers: sonnet (general), gpt (general), security (focused)

.gitea/actions/review/action.yml

@@ -70,6 +70,10 @@ inputs:
     description: 'Delete previous review from same bot before posting. Accepts: true/1/yes or false/0/no (default true)'
     required: false
     default: 'true'
+  system-prompt-file:
+    description: 'Local file with additional system prompt instructions (e.g. security review focus)'
+    required: false
+    default: ''
 
 runs:
   using: 'composite'
@@ -150,6 +154,7 @@ runs:
         LLM_TIMEOUT: ${{ inputs.timeout }}
         LLM_PROVIDER: ${{ inputs.llm-provider }}
         UPDATE_EXISTING: ${{ inputs.update-existing }}
+        SYSTEM_PROMPT_FILE: ${{ inputs.system-prompt-file }}
       run: |
         ARGS=""
         if [ "${{ inputs.dry-run }}" = "true" ]; then

.gitea/workflows/ci.yml

@@ -32,6 +32,10 @@ jobs:
           - name: gpt
             token_secret: GPT_REVIEW_TOKEN
             model: gpt-4.1
+          - name: security
+            token_secret: SONNET_REVIEW_TOKEN
+            model: gpt-5
+            system_prompt_file: SECURITY_REVIEW.md
     steps:
       - uses: actions/checkout@v4
       - uses: actions/setup-go@v5
@@ -44,6 +48,7 @@ jobs:
           GITEA_REPO: ${{ github.repository }}
           PR_NUMBER: ${{ github.event.pull_request.number }}
           REVIEWER_TOKEN: ${{ secrets[matrix.token_secret] }}
+          REVIEWER_NAME: ${{ matrix.name }}
           LLM_BASE_URL: ${{ secrets.LLM_BASE_URL }}
           LLM_API_KEY: ${{ secrets.LLM_API_KEY }}
           LLM_MODEL: ${{ matrix.model }}
@@ -51,4 +56,5 @@ jobs:
           PATTERNS_REPO: "rodin/go-patterns"
           PATTERNS_FILES: "README.md,patterns/"
           LLM_TIMEOUT: "600"
+          SYSTEM_PROMPT_FILE: ${{ matrix.system_prompt_file }}
         run: ./review-bot

SECURITY_REVIEW.md

@@ -0,0 +1,18 @@
+You are performing a security-focused code review. Your primary concern is identifying vulnerabilities, not general code quality.
+
+Focus areas:
+- **Injection attacks**: SQL injection, command injection, path traversal, template injection
+- **Authentication/Authorization**: Missing auth checks, privilege escalation, IDOR
+- **Secrets exposure**: Hardcoded credentials, API keys in code, tokens in logs
+- **Input validation**: Untrusted input used without sanitization, unsafe deserialization
+- **Cryptography**: Weak algorithms, predictable randomness, improper key management
+- **Error handling**: Information leakage in error messages, stack traces exposed
+- **Dependencies**: Known vulnerable patterns, unsafe use of external libraries
+- **Race conditions**: TOCTOU bugs, unsynchronized shared state
+- **Resource exhaustion**: Unbounded allocations, missing timeouts, denial-of-service vectors
+
+Rules for this review:
+- Only report findings with actual security implications. Ignore style, naming, and general code quality.
+- Severity mapping: MAJOR = exploitable vulnerability or data exposure. MINOR = defense-in-depth improvement or hardening opportunity. NIT = theoretical concern with low practical risk.
+- If the code has no security-relevant changes, APPROVE with an empty findings list.
+- Do not duplicate findings that a standard code review would catch (logic bugs, missing error checks) unless they have a security dimension.

cmd/review-bot/main.go

@@ -30,6 +30,7 @@ func main() {
 	llmAPIKey := flag.String("llm-api-key", envOrDefault("LLM_API_KEY", ""), "LLM API key")
 	llmModel := flag.String("llm-model", envOrDefault("LLM_MODEL", ""), "LLM model name")
 	conventionsFile := flag.String("conventions-file", envOrDefault("CONVENTIONS_FILE", ""), "Conventions file path in repo (e.g. CLAUDE.md)")
+	systemPromptFile := flag.String("system-prompt-file", envOrDefault("SYSTEM_PROMPT_FILE", ""), "Local file with additional system prompt instructions")
 	patternsRepo := flag.String("patterns-repo", envOrDefault("PATTERNS_REPO", ""), "Repo with language patterns (e.g. rodin/elixir-patterns)")
 	patternsFiles := flag.String("patterns-files", envOrDefault("PATTERNS_FILES", "README.md"), "Comma-separated file paths to fetch from patterns repo")
 	dryRun := flag.Bool("dry-run", false, "Print review to stdout instead of posting")
@@ -150,9 +151,24 @@ func main() {
 		log.Printf("Loaded patterns from %s (%d bytes)", *patternsRepo, len(patterns))
 	}
 
+	// Step 6b: Load additional system prompt if specified
+	additionalPrompt := ""
+	if *systemPromptFile != "" {
+		data, err := os.ReadFile(*systemPromptFile)
+		if err != nil {
+			log.Fatalf("Failed to read system prompt file %q: %v", *systemPromptFile, err)
+		}
+		additionalPrompt = string(data)
+		log.Printf("Loaded system prompt file: %s (%d bytes)", *systemPromptFile, len(additionalPrompt))
+	}
+
 	// Step 7: Budget-aware prompt assembly
+	systemBase := review.BuildSystemBase()
+	if additionalPrompt != "" {
+		systemBase += "\n\n## Additional Review Instructions\n\n" + additionalPrompt
+	}
 	sections := budget.Sections{
-		SystemBase:  review.BuildSystemBase(),
+		SystemBase:  systemBase,
 		Patterns:    patterns,
 		Conventions: conventions,
 		FileContext: fileContext,
@@ -203,14 +219,15 @@ func main() {
 	}
 	log.Printf("Review posted (id=%d, user=%s)", posted.ID, posted.User.Login)
 
-	// Delete stale reviews from this bot if update-existing is enabled
-	if *updateExisting && posted.User.Login != "" {
+	// Delete stale reviews from this bot using sentinel matching
+	sentinel := fmt.Sprintf("<!-- review-bot:%s -->", *reviewerName)
+	if *updateExisting && *reviewerName != "" {
 		reviews, err := giteaClient.ListReviews(ctx, owner, repoName, prNumber)
 		if err != nil {
 			log.Printf("Warning: could not list existing reviews: %v", err)
 		} else {
 			for _, r := range reviews {
-				if r.User.Login == posted.User.Login && r.ID != posted.ID {
+				if r.ID != posted.ID && strings.Contains(r.Body, sentinel) {
 					if err := giteaClient.DeleteReview(ctx, owner, repoName, prNumber, r.ID); err != nil {
 						log.Printf("Warning: could not delete old review %d: %v", r.ID, err)
 					} else {

gitea/client.go

@@ -279,6 +279,7 @@ func (c *Client) GetAllFilesInPath(ctx context.Context, owner, repo, path string
 // Review represents a pull request review from the Gitea API.
 type Review struct {
 	ID   int64  `json:"id"`
+	Body string `json:"body"`
 	User struct {
 		Login string `json:"login"`
 	} `json:"user"`

review/formatter.go

@@ -30,6 +30,8 @@ func FormatMarkdown(result *ReviewResult, reviewerName string) string {
 
 	if reviewerName != "" {
 		sb.WriteString(fmt.Sprintf("\n---\n*Review by %s*\n", reviewerName))
+		// Hidden sentinel for identifying this bot's reviews during cleanup
+		sb.WriteString(fmt.Sprintf("\n<!-- review-bot:%s -->\n", reviewerName))
 	}
 
 	return sb.String()

review/formatter_test.go

@@ -116,3 +116,21 @@ func TestGiteaEvent(t *testing.T) {
 		}
 	}
 }
+
+func TestFormatMarkdown_Sentinel(t *testing.T) {
+	result := &ReviewResult{
+		Verdict:        "APPROVE",
+		Summary:        "All good.",
+		Recommendation: "Merge it.",
+	}
+	output := FormatMarkdown(result, "security")
+	if !strings.Contains(output, "<!-- review-bot:security -->") {
+		t.Error("expected sentinel comment in output")
+	}
+
+	// Empty reviewer name should NOT have sentinel
+	output2 := FormatMarkdown(result, "")
+	if strings.Contains(output2, "<!-- review-bot") {
+		t.Error("should not contain sentinel when reviewer name is empty")
+	}
+}