fix: address review findings (comment, marker budget, naming)

- UserMeta comment: "never trimmed" → "truncated only if base exceeds budget"
- Skip diff truncation marker when diffBudget < markerBudget (prevents
  marker itself from pushing EstTokens over the limit)
- Rename filepath → filePath to avoid shadowing stdlib package name

.gitea/workflows/ci.yml

@@ -31,7 +31,7 @@ jobs:
             model: gpt-5
           - name: gpt
             token_secret: GPT_REVIEW_TOKEN
-            model: gpt-5-mini
+            model: gpt-4.1
     steps:
       - uses: actions/checkout@v4
       - uses: actions/setup-go@v5
@@ -49,5 +49,6 @@ jobs:
           LLM_MODEL: ${{ matrix.model }}
           CONVENTIONS_FILE: "CONVENTIONS.md"
           PATTERNS_REPO: "rodin/go-patterns"
-          PATTERNS_FILES: "README.md,docs/"
+          PATTERNS_FILES: "README.md,patterns/"
+          LLM_TIMEOUT: "600"
         run: ./review-bot

.gitea/workflows/release.yml

@@ -16,7 +16,9 @@ jobs:
           go-version: '1.26'
 
       - name: Run tests
-        run: go test ./...
+        run: |
+          go vet ./...
+          go test ./...
 
       - name: Build binaries
         run: |

REVIEW.md

@@ -0,0 +1,436 @@
+# review-bot Code Review (vs go-patterns)
+
+## Overall Assessment
+
+The review-bot is a well-structured, focused Go application that follows many idiomatic patterns correctly. The package layout is clean (`gitea/`, `llm/`, `review/`, `cmd/`), error handling uses `%w` wrapping consistently, and the test suite covers all major code paths using `httptest`. However, there are several areas where the code diverges from the patterns documented in `go-patterns` — particularly around configuration, context propagation, exported fields, documentation, and testing idioms.
+
+**Verdict: Solid foundation with targeted improvements needed.**
+
+## Findings
+
+| # | Severity | File | Pattern Violated | Finding |
+|---|----------|------|-----------------|---------|
+| 1 | MAJOR | `gitea/client.go` | concurrency / api-conventions | No `context.Context` parameter on any method — HTTP calls are uncancellable |
+| 2 | MAJOR | `llm/client.go` | concurrency / api-conventions | `Complete()` accepts no context — no timeout or cancellation support |
+| 3 | MAJOR | `gitea/client.go` | structs / encapsulation | `Client` fields (`BaseURL`, `Token`, `HTTP`) are exported but should be unexported |
+| 4 | MAJOR | `llm/client.go` | structs / encapsulation | `Client` fields (`BaseURL`, `APIKey`, `Model`, `HTTP`) are exported — leaks credentials via reflection/logging |
+| 5 | MINOR | `cmd/review-bot/main.go` | configuration | No input validation beyond emptiness — e.g., URL format, model name format |
+| 6 | MINOR | `cmd/review-bot/main.go` | error-handling | Uses `log.Fatalf` for all errors — no cleanup, deferred functions won't run |
+| 7 | MINOR | `gitea/client.go` | error-handling / style | Error strings in `doGet` are inconsistent — some use `fmt.Errorf`, the raw HTTP error doesn't wrap with `%w` |
+| 8 | MINOR | `review/prompt.go` | style / api-conventions | `BuildSystemPrompt` uses 20+ `WriteString` calls — could use a raw string literal for readability |
+| 9 | MINOR | `gitea/client.go` | documentation | No concurrency safety documentation on `Client` type |
+| 10 | MINOR | `llm/client.go` | documentation | No concurrency safety documentation on `Client` type |
+| 11 | MINOR | `gitea/client_test.go` | testing-advanced | Tests don't use `t.Run` subtests — individual test functions instead of table-driven with named cases |
+| 12 | MINOR | `integration_test.go` | style | Uses rune literal `'/'` comparison in a loop instead of `strings.SplitN` (inconsistent with `main.go`) |
+| 13 | MINOR | `llm/client.go` | configuration | `Temperature: 0.1` is hardcoded — not configurable and the zero-value (0.0) semantic isn't clear |
+| 14 | NIT | `gitea/client.go` | style | `PostReview` converts `[]byte` to `string` then passes to `strings.NewReader` — use `bytes.NewReader(data)` directly |
+| 15 | NIT | `review/formatter.go` | documentation | `GiteaEvent` has no doc comment explaining the mapping semantics |
+| 16 | NIT | `cmd/review-bot/main.go` | package-design | `evaluateCIStatus` is unexported logic in `main` — could live in `review` package for testability |
+| 17 | NIT | `gitea/client.go` | interfaces | No interface defined for the Gitea client — makes the main function harder to unit test |
+| 18 | NIT | `llm/client.go` | interfaces | No interface defined for the LLM client — same testability concern |
+| 19 | NIT | `review/parser.go` | error-handling | `extractJSON` silently handles malformed fences — edge case: `\`\`\`` with only 1 line produces empty string |
+| 20 | NIT | Various | documentation | No package-level doc comments (`// Package xxx ...`) on any package |
+
+## Detailed Findings
+
+### 1. No `context.Context` on Gitea client methods (MAJOR)
+
+**What the code does:**
+```go
+func (c *Client) GetPullRequest(owner, repo string, number int) (*PullRequest, error) {
+    url := fmt.Sprintf(...)
+    body, err := c.doGet(url)
+    ...
+}
+```
+
+**What the pattern says:**
+From `concurrency.md` §6 (Context Propagation Rules): "Pass a Context explicitly to each function that needs it. The Context should be the first parameter, typically named ctx." From `api-conventions.md` §3 (WithContext variant): All I/O-performing functions should accept a context for timeout/cancellation.
+
+**How to fix:**
+```go
+func (c *Client) GetPullRequest(ctx context.Context, owner, repo string, number int) (*PullRequest, error) {
+    ...
+    req, err := http.NewRequestWithContext(ctx, "GET", url, nil)
+    ...
+}
+```
+
+Add `context.Context` as the first parameter to all public methods. Update `doGet` to accept context internally.
+
+---
+
+### 2. No `context.Context` on LLM `Complete()` (MAJOR)
+
+**What the code does:**
+```go
+func (c *Client) Complete(messages []Message) (string, error) {
+    ...
+    req, err := http.NewRequest("POST", url, bytes.NewReader(data))
+    ...
+}
+```
+
+**What the pattern says:**
+Same as finding #1. LLM calls can take 30-60+ seconds. Without context, there's no way to enforce a timeout or cancel a review that's taking too long.
+
+**How to fix:**
+```go
+func (c *Client) Complete(ctx context.Context, messages []Message) (string, error) {
+    ...
+    req, err := http.NewRequestWithContext(ctx, "POST", url, bytes.NewReader(data))
+    ...
+}
+```
+
+The caller in `main.go` should create a context with timeout: `ctx, cancel := context.WithTimeout(context.Background(), 2*time.Minute)`.
+
+---
+
+### 3 & 4. Exported struct fields on Client types (MAJOR)
+
+**What the code does:**
+```go
+type Client struct {
+    BaseURL string
+    Token   string
+    HTTP    *http.Client
+}
+```
+
+**What the pattern says:**
+From `structs.md`: use unexported fields for internal state; expose only what callers need to read/modify. From `configuration.md` §9: Document immutability constraints. Exported fields like `Token` and `APIKey` are sensitive credentials that could be accidentally logged, serialized, or mutated after construction.
+
+**How to fix:**
+```go
+type Client struct {
+    baseURL string
+    token   string
+    http    *http.Client
+}
+```
+
+If tests need to override `HTTP`, expose it via a functional option or a `WithHTTPClient(*http.Client)` setter, or accept it in the constructor.
+
+---
+
+### 5. No input validation beyond emptiness (MINOR)
+
+**What the code does:**
+```go
+if *giteaURL == "" || *repo == "" || ...
+```
+
+**What the pattern says:**
+From `configuration.md` §1 (Zero-Value Config): Document and validate configuration explicitly. A malformed URL (e.g., missing scheme) will produce a confusing error later during HTTP request creation rather than at startup.
+
+**How to fix:**
+```go
+if _, err := url.Parse(*giteaURL); err != nil || !strings.HasPrefix(*giteaURL, "http") {
+    log.Fatalf("Invalid --gitea-url: %s", *giteaURL)
+}
+```
+
+---
+
+### 6. `log.Fatalf` for all errors (MINOR)
+
+**What the code does:**
+`log.Fatalf(...)` is used for every error in `main()`.
+
+**What the pattern says:**
+From `api-conventions.md` §9 (Graceful Shutdown): distinguish between fatal and recoverable errors. From `error-handling.md`: error handling should give callers the ability to respond. While `main()` is the top-level caller, `log.Fatalf` calls `os.Exit(1)` which doesn't run deferred functions.
+
+**How to fix:**
+Use a `run() error` pattern:
+```go
+func main() {
+    if err := run(); err != nil {
+        fmt.Fprintf(os.Stderr, "error: %v\n", err)
+        os.Exit(1)
+    }
+}
+
+func run() error { ... }
+```
+
+This allows deferred cleanup to run and makes the code testable.
+
+---
+
+### 7. Inconsistent error formatting in `doGet` (MINOR)
+
+**What the code does:**
+```go
+func (c *Client) doGet(url string) ([]byte, error) {
+    ...
+    return nil, fmt.Errorf("HTTP %d: %s", resp.StatusCode, string(body))
+}
+```
+The error from the raw HTTP response isn't wrapped with `%w`, but the callers wrap it again: `fmt.Errorf("fetch PR: %w", err)`. The inner error starts with a capital "HTTP".
+
+**What the pattern says:**
+From `smells/anti-patterns.md` §6 (Error String Formatting): error strings should be lowercase. They compose upward: `fetch PR: HTTP 404: ...` has inconsistent casing.
+
+**How to fix:**
+```go
+return nil, fmt.Errorf("http %d: %s", resp.StatusCode, string(body))
+```
+
+---
+
+### 8. Prompt building uses excessive `WriteString` (MINOR)
+
+**What the code does:**
+```go
+sb.WriteString("You are an expert code reviewer...\n\n")
+sb.WriteString("Your task:\n")
+sb.WriteString("1. Review the diff...\n")
+// ... 20+ more lines
+```
+
+**What the pattern says:**
+From `style.md`: code should be readable and maintainable. A raw string literal would be far more readable for a multi-line prompt template.
+
+**How to fix:**
+```go
+const systemPromptTemplate = `You are an expert code reviewer. Review the provided pull request diff carefully.
+
+Your task:
+1. Review the diff for correctness, idiomatic code, potential bugs, and design issues.
+...
+`
+
+func BuildSystemPrompt(conventions string) string {
+    prompt := systemPromptTemplate
+    if conventions != "" {
+        prompt += fmt.Sprintf("\n\nThe repository has the following coding conventions...\n\n%s\n", conventions)
+    }
+    return prompt
+}
+```
+
+---
+
+### 9 & 10. No concurrency safety documentation (MINOR)
+
+**What the code does:**
+Neither `gitea.Client` nor `llm.Client` documents whether they're safe for concurrent use.
+
+**What the pattern says:**
+From `documentation.md` §9 (Concurrency Documentation): "Doc comments explicitly state the concurrency safety of a type." Since both types embed `*http.Client` (which IS safe for concurrent use), the wrapping types should document this.
+
+**How to fix:**
+```go
+// Client interacts with the Gitea API.
+// A Client is safe for concurrent use by multiple goroutines.
+type Client struct { ... }
+```
+
+---
+
+### 11. Tests don't use `t.Run` subtests (MINOR)
+
+**What the code does:**
+`gitea/client_test.go` defines 8 separate `TestXxx` functions, each creating their own httptest server.
+
+**What the pattern says:**
+From `testing-advanced.md` §1 (Table-Driven Tests with `t.Run`): related tests should use named subtests for filterability and clarity. The Gitea client tests share identical setup patterns — they'd benefit from a shared helper.
+
+**How to fix:**
+Consider a test helper that creates a server with a handler map, then use `t.Run` for each case. The existing structure is acceptable but could be DRYer.
+
+---
+
+### 12. Inconsistent repo parsing in `integration_test.go` (MINOR)
+
+**What the code does:**
+```go
+for i, c := range giteaRepo {
+    if c == '/' {
+        owner = giteaRepo[:i]
+        repoName = giteaRepo[i+1:]
+        break
+    }
+}
+```
+
+**What the pattern says:**
+From `style.md` §3 (File Organization by Responsibility): related logic should be consistent. `main.go` uses `strings.SplitN(*repo, "/", 2)` for the same operation. The integration test reinvents it with a manual loop.
+
+**How to fix:**
+Use `strings.SplitN(giteaRepo, "/", 2)` for consistency, or extract a shared helper.
+
+---
+
+### 13. Hardcoded `Temperature: 0.1` (MINOR)
+
+**What the code does:**
+```go
+reqBody := ChatRequest{
+    ...
+    Temperature: 0.1,
+}
+```
+
+**What the pattern says:**
+From `configuration.md` §1 (Zero-Value Usable Config): "Every field documents its zero-value behavior." The temperature is buried in implementation. It should be configurable (e.g., a field on `Client` with a documented default).
+
+**How to fix:**
+Add a `Temperature` field to `Client` with documentation:
+```go
+type Client struct {
+    ...
+    // Temperature controls LLM randomness. If zero, defaults to 0.1.
+    Temperature float64
+}
+```
+
+---
+
+### 14. Unnecessary `string()` → `strings.NewReader` conversion (NIT)
+
+**What the code does:**
+```go
+data, err := json.Marshal(payload)
+...
+req, err := http.NewRequest("POST", url, strings.NewReader(string(data)))
+```
+
+**What the pattern says:**
+From `style.md`: avoid unnecessary allocations. `json.Marshal` returns `[]byte`; use `bytes.NewReader(data)` directly to avoid the `[]byte→string` copy.
+
+**How to fix:**
+```go
+req, err := http.NewRequest("POST", url, bytes.NewReader(data))
+```
+
+---
+
+### 15. Missing doc comment on `GiteaEvent` (NIT)
+
+**What the code does:**
+```go
+// GiteaEvent converts the verdict to the Gitea API event string.
+func GiteaEvent(verdict string) string {
+```
+
+Actually, this one DOES have a doc comment. On closer inspection the comment exists. Removing this finding — **correction**: the comment is present but minimal. It doesn't document the mapping or the "COMMENT" fallback behavior. This is borderline.
+
+---
+
+### 16. `evaluateCIStatus` in `main` package (NIT)
+
+**What the code does:**
+The `evaluateCIStatus` function lives in `cmd/review-bot/main.go` and operates on `[]gitea.CommitStatus`.
+
+**What the pattern says:**
+From `package-design.md`: packages should encapsulate related logic. This function interprets CI status semantics — it belongs in the `review` package (or even `gitea`) where it could be unit-tested independently without building the entire binary.
+
+---
+
+### 17 & 18. No interfaces for testability (NIT)
+
+**What the code does:**
+`main.go` directly uses `*gitea.Client` and `*llm.Client` concrete types.
+
+**What the pattern says:**
+From `interfaces.md`: "Define interfaces in the package that USES them." From `smells/common-mistakes.md` §10 (Premature Abstraction): don't create interfaces before you need them. However, the consumer (`main.go`) would benefit from small interfaces for testing the orchestration logic independently.
+
+**How to fix (when needed):**
+```go
+// In main or a review orchestrator package:
+type PRFetcher interface {
+    GetPullRequest(ctx context.Context, owner, repo string, number int) (*gitea.PullRequest, error)
+    GetPullRequestDiff(ctx context.Context, owner, repo string, number int) (string, error)
+}
+```
+
+Note: This is a NIT because the current code doesn't have tests for `main.go` orchestration. If/when that's needed, interfaces become valuable.
+
+---
+
+### 19. `extractJSON` edge case (NIT)
+
+**What the code does:**
+```go
+if strings.HasPrefix(s, "```") {
+    lines := strings.Split(s, "\n")
+    if len(lines) > 2 {
+        lines = lines[1:]
+    }
+    ...
+}
+```
+
+If input is exactly `` ```json\n``` `` (fence with empty body), it produces an empty string that will fail JSON parse with a confusing error message.
+
+**What the pattern says:**
+From `error-handling.md`: errors should carry context. Consider returning an explicit error from `extractJSON` when the extracted content is empty after fence stripping.
+
+---
+
+### 20. No package doc comments (NIT)
+
+**What the code does:**
+None of the packages (`gitea`, `llm`, `review`) have `// Package xxx ...` doc comments.
+
+**What the pattern says:**
+From `documentation.md` §1 (Package Documentation): "The first file in a package starts with a `// Package xxx ...` comment that explains the package's purpose."
+
+**How to fix:**
+Add to each package's primary file:
+```go
+// Package gitea provides a client for the Gitea API, focused on pull request review operations.
+package gitea
+```
+
+---
+
+## Positive Patterns
+
+The codebase does several things well:
+
+1. **Clean package separation** — `gitea/`, `llm/`, `review/`, `cmd/` each have a single responsibility. This matches `package-design.md` perfectly.
+
+2. **Consistent error wrapping** — Every public function wraps errors with `fmt.Errorf("context: %w", err)`, providing clear error chains. This follows `error-handling.md` closely.
+
+3. **Return concrete types from constructors** — `NewClient()` returns `*Client`, not an interface. Matches `smells/common-mistakes.md` §7 and `smells/anti-patterns.md` §8.
+
+4. **httptest-based testing** — Both client packages use `net/http/httptest` for isolated, deterministic tests. No external dependencies needed.
+
+5. **Good test coverage of error paths** — Tests cover 404s, bad JSON, connection failures, invalid severities, missing fields. This is thorough.
+
+6. **Zero dependencies** — `go.mod` has no external dependencies. The entire project uses only the standard library. This is excellent for a focused tool.
+
+7. **Build-tagged integration test** — The `//go:build integration` tag keeps expensive tests separate from unit tests. Good practice.
+
+8. **`strings.Builder` usage** — Prompt building and formatting use `strings.Builder` correctly for efficient string construction.
+
+9. **Named return values where useful** — `evaluateCIStatus` uses named returns `(passed bool, details string)` for documentation clarity, matching `style.md` §5.
+
+10. **No premature abstraction** — The code doesn't define interfaces it doesn't need yet. It's concrete and straightforward, following `smells/common-mistakes.md` §10.
+
+## Recommendations
+
+Priority-ordered list of improvements:
+
+1. **Add `context.Context` to all client methods** (Critical) — This is the single most impactful change. LLM calls can hang indefinitely without timeout support. Both `gitea.Client` and `llm.Client` should accept context as the first parameter on all public methods. Use `http.NewRequestWithContext`.
+
+2. **Unexport client struct fields** (High) — `Token`, `APIKey`, `BaseURL` should be unexported to prevent accidental logging/serialization of credentials. Expose only what's needed via methods or constructor options.
+
+3. **Add package documentation** (Medium) — Each package needs a `// Package xxx ...` comment. This takes 5 minutes and significantly improves discoverability.
+
+4. **Extract `evaluateCIStatus` to `review` package** (Medium) — Makes it independently testable and keeps `main.go` focused on orchestration.
+
+5. **Use `run() error` pattern in main** (Medium) — Enables deferred cleanup and makes the orchestration logic more testable.
+
+6. **Replace `WriteString` chain with raw string literal** (Low) — Pure readability improvement for `BuildSystemPrompt`.
+
+7. **Make LLM temperature configurable** (Low) — Add as a field on `Client` with documented zero-value default.
+
+8. **Use `bytes.NewReader` instead of `strings.NewReader(string(...))` in PostReview** (Low) — Eliminates one unnecessary allocation.
+
+9. **Add concurrency documentation to Client types** (Low) — One-line doc additions.
+
+10. **Consider consumer-side interfaces when testing `main` orchestration** (Future) — Not needed now, but will become valuable if the `main.go` logic grows or needs unit testing.

budget/budget.go

@@ -0,0 +1,226 @@
+// Package budget manages LLM context window budgeting for review-bot.
+//
+// It estimates token usage and progressively trims context content to fit
+// within model-specific limits. The trimming order (least important first):
+// patterns → conventions → file context → diff truncation.
+package budget
+
+import (
+	"fmt"
+	"strings"
+	"unicode/utf8"
+)
+
+// modelLimit pairs a model name prefix with its context window size.
+type modelLimit struct {
+	prefix string
+	limit  int
+}
+
+// Known model context limits (in tokens), ordered longest-prefix-first
+// for deterministic matching.
+var modelLimits = []modelLimit{
+	{"claude-haiku-3.5-20241022", 200_000},
+	{"claude-sonnet-4-20250514", 200_000},
+	{"claude-opus-4-20250514", 200_000},
+	{"gpt-4.1-mini", 128_000},
+	{"gpt-5-mini", 200_000},
+	{"gpt-4.1", 128_000},
+	{"gpt-5", 200_000},
+}
+
+const defaultLimit = 128_000
+
+// reserveTokens is headroom for the response generation.
+const reserveTokens = 4_000
+
+const diffTruncMarker = "\n\n... [diff truncated due to context limit] ..."
+const diffTooLargeMarker = "... [diff too large for context window — review manually] ..."
+const userMetaTruncMarker = "\n... [description truncated] ..."
+
+// EstimateTokens estimates the number of tokens in a string.
+// Uses the rough heuristic of ~4 bytes per token, which is
+// conservative for English text and code.
+func EstimateTokens(s string) int {
+	return len(s) / 4
+}
+
+// LimitForModel returns the context window size for the given model.
+// Uses longest-prefix-first matching for deterministic results.
+func LimitForModel(model string) int {
+	for _, ml := range modelLimits {
+		if model == ml.prefix || strings.HasPrefix(model, ml.prefix) {
+			return ml.limit
+		}
+	}
+	return defaultLimit
+}
+
+// Sections holds the prompt content sections in trim priority order.
+// When the total exceeds the budget, sections are trimmed from least
+// important (Patterns) to most important (Diff).
+type Sections struct {
+	SystemBase  string // Core instructions (never trimmed)
+	Patterns    string // Language patterns (trimmed first)
+	Conventions string // Repo conventions (trimmed second)
+	FileContext string // Full file content (trimmed third)
+	Diff        string // The actual diff (trimmed last, only truncated)
+	UserMeta    string // PR title, description, CI status (truncated only if base exceeds budget)
+}
+
+// Result holds the trimmed content and metadata about what was dropped.
+type Result struct {
+	SystemPrompt string
+	UserPrompt   string
+	Trimmed      []string // Human-readable descriptions of what was trimmed
+	EstTokens    int      // Estimated total tokens after trimming
+}
+
+// Fit trims sections to fit within the model's context limit.
+// Returns the assembled prompts and a list of what was trimmed.
+func Fit(model string, sections Sections) Result {
+	limit := LimitForModel(model) - reserveTokens
+
+	baseTokens := EstimateTokens(sections.SystemBase) + EstimateTokens(sections.UserMeta)
+	available := limit - baseTokens
+	if available < 0 {
+		// Base content alone exceeds budget. Truncate UserMeta (keep first ~1000 tokens).
+		if len(sections.UserMeta) > 4000 {
+			sections.UserMeta = truncateUTF8(sections.UserMeta, 4000) + userMetaTruncMarker
+			baseTokens = EstimateTokens(sections.SystemBase) + EstimateTokens(sections.UserMeta)
+			available = limit - baseTokens
+		}
+		if available < 0 {
+			available = 0
+		}
+	}
+
+	// Trimmable sections in priority order (first = dropped first)
+	type entry struct {
+		name    string
+		content *string
+	}
+	entries := []entry{
+		{"patterns", &sections.Patterns},
+		{"conventions", &sections.Conventions},
+		{"file context", &sections.FileContext},
+	}
+
+	// Check if everything fits
+	totalTrimmable := EstimateTokens(sections.Diff)
+	for _, e := range entries {
+		totalTrimmable += EstimateTokens(*e.content)
+	}
+
+	var trimmed []string
+	if totalTrimmable > available {
+		// Trim from least important
+		for i := range entries {
+			tokens := EstimateTokens(*entries[i].content)
+			if tokens == 0 {
+				continue
+			}
+			trimmed = append(trimmed, fmt.Sprintf("%s (~%dK tokens)", entries[i].name, tokens/1000))
+			*entries[i].content = ""
+
+			// Recalculate
+			totalTrimmable = EstimateTokens(sections.Diff)
+			for _, e := range entries {
+				totalTrimmable += EstimateTokens(*e.content)
+			}
+			if totalTrimmable <= available {
+				break
+			}
+		}
+	}
+
+	// If still too large, truncate the diff
+	if totalTrimmable > available {
+		diffBudget := available
+		for _, e := range entries {
+			diffBudget -= EstimateTokens(*e.content)
+		}
+		if diffBudget < 0 {
+			diffBudget = 0
+		}
+		// Reserve space for truncation marker
+		markerBudget := EstimateTokens(diffTruncMarker)
+		effectiveBudget := diffBudget - markerBudget
+		if effectiveBudget < 0 {
+			effectiveBudget = 0
+		}
+		maxChars := effectiveBudget * 4
+		if maxChars < len(sections.Diff) {
+			removed := EstimateTokens(sections.Diff) - diffBudget
+			trimmed = append(trimmed, fmt.Sprintf("diff truncated (~%dK tokens removed)", removed/1000))
+			if maxChars > 0 {
+				if diffBudget >= markerBudget {
+					sections.Diff = truncateUTF8(sections.Diff, maxChars) + diffTruncMarker
+				} else {
+					sections.Diff = truncateUTF8(sections.Diff, maxChars)
+				}
+			} else {
+				sections.Diff = diffTooLargeMarker
+			}
+		}
+	}
+
+	finalTokens := baseTokens
+	for _, e := range entries {
+		finalTokens += EstimateTokens(*e.content)
+	}
+	finalTokens += EstimateTokens(sections.Diff)
+
+	return buildResult(sections, trimmed, finalTokens)
+}
+
+func buildResult(s Sections, trimmed []string, estTokens int) Result {
+	var sys strings.Builder
+	sys.WriteString(s.SystemBase)
+	if s.Patterns != "" {
+		sys.WriteString("\n\n## Language Patterns & Idioms\n\nUse the following patterns as review criteria. Code that violates these established patterns is a finding:\n\n")
+		sys.WriteString(s.Patterns)
+	}
+	if s.Conventions != "" {
+		sys.WriteString("\n\n## Repository Conventions\n\nThe repository has the following coding conventions that must be respected:\n\n")
+		sys.WriteString(s.Conventions)
+	}
+
+	var usr strings.Builder
+	usr.WriteString(s.UserMeta)
+	if s.FileContext != "" {
+		usr.WriteString("\n### Full File Context (modified files)\n\n")
+		usr.WriteString(s.FileContext)
+		usr.WriteString("\n")
+	}
+	if s.Diff != "" {
+		usr.WriteString("\n### Diff (changes to review)\n\n```diff\n")
+		usr.WriteString(s.Diff)
+		usr.WriteString("\n```\n")
+	}
+
+	if len(trimmed) > 0 {
+		usr.WriteString("\n⚠️ Note: Context was trimmed to fit model limits. Dropped: ")
+		usr.WriteString(strings.Join(trimmed, ", "))
+		usr.WriteString("\n")
+	}
+
+	return Result{
+		SystemPrompt: sys.String(),
+		UserPrompt:   usr.String(),
+		Trimmed:      trimmed,
+		EstTokens:    estTokens,
+	}
+}
+
+// truncateUTF8 truncates s to at most maxBytes without splitting multi-byte
+// UTF-8 characters. Returns a valid UTF-8 string of at most maxBytes bytes.
+func truncateUTF8(s string, maxBytes int) string {
+	if len(s) <= maxBytes {
+		return s
+	}
+	for maxBytes > 0 && !utf8.RuneStart(s[maxBytes]) {
+		maxBytes--
+	}
+	return s[:maxBytes]
+}

budget/budget_test.go

@@ -0,0 +1,203 @@
+package budget
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestEstimateTokens(t *testing.T) {
+	tests := []struct {
+		input string
+		want  int
+	}{
+		{"", 0},
+		{"abcd", 1},
+		{"12345678", 2},
+		{strings.Repeat("x", 400), 100},
+	}
+	for _, tt := range tests {
+		got := EstimateTokens(tt.input)
+		if got != tt.want {
+			t.Errorf("EstimateTokens(%d chars) = %d, want %d", len(tt.input), got, tt.want)
+		}
+	}
+}
+
+func TestLimitForModel(t *testing.T) {
+	tests := []struct {
+		model string
+		want  int
+	}{
+		{"gpt-4.1", 128_000},
+		{"gpt-5", 200_000},
+		{"gpt-5-mini", 200_000},
+		{"unknown-model", defaultLimit},
+		{"gpt-4.1-2026-01-01", 128_000}, // prefix match
+	}
+	for _, tt := range tests {
+		got := LimitForModel(tt.model)
+		if got != tt.want {
+			t.Errorf("LimitForModel(%q) = %d, want %d", tt.model, got, tt.want)
+		}
+	}
+}
+
+func TestFit_AllFits(t *testing.T) {
+	s := Sections{
+		SystemBase:  "system instructions",
+		Patterns:    "some patterns",
+		Conventions: "some conventions",
+		FileContext: "file content",
+		Diff:        "diff content",
+		UserMeta:    "PR: title\n",
+	}
+	result := Fit("gpt-5", s)
+
+	if len(result.Trimmed) != 0 {
+		t.Errorf("expected no trimming, got %v", result.Trimmed)
+	}
+	if !strings.Contains(result.SystemPrompt, "some patterns") {
+		t.Error("expected patterns in system prompt")
+	}
+	if !strings.Contains(result.SystemPrompt, "some conventions") {
+		t.Error("expected conventions in system prompt")
+	}
+	if !strings.Contains(result.UserPrompt, "file content") {
+		t.Error("expected file context in user prompt")
+	}
+}
+
+func TestFit_TrimsPatterns(t *testing.T) {
+	// Create content that exceeds 128K token budget for gpt-4.1
+	// Budget ≈ 128K - 4K reserve = 124K tokens = ~496K chars
+	// Fill patterns with enough to push over
+	bigPatterns := strings.Repeat("x", 500_000) // ~125K tokens
+	s := Sections{
+		SystemBase:  "base",
+		Patterns:    bigPatterns,
+		Conventions: "conventions",
+		FileContext: "files",
+		Diff:        "diff",
+		UserMeta:    "meta",
+	}
+	result := Fit("gpt-4.1", s)
+
+	if len(result.Trimmed) == 0 {
+		t.Fatal("expected trimming")
+	}
+	if !strings.Contains(result.Trimmed[0], "patterns") {
+		t.Errorf("expected patterns to be trimmed first, got %v", result.Trimmed)
+	}
+	if strings.Contains(result.SystemPrompt, bigPatterns[:100]) {
+		t.Error("expected patterns to be removed from output")
+	}
+	// Conventions should survive
+	if !strings.Contains(result.SystemPrompt, "conventions") {
+		t.Error("expected conventions to survive after patterns trimmed")
+	}
+}
+
+func TestFit_TrimsConventions(t *testing.T) {
+	// Patterns + conventions + diff all exceed budget even after patterns removed
+	big := strings.Repeat("y", 520_000) // ~130K tokens each (exceeds 124K budget even alone)
+	s := Sections{
+		SystemBase:  "base",
+		Patterns:    big,
+		Conventions: big,
+		FileContext: "files",
+		Diff:        "diff",
+		UserMeta:    "meta",
+	}
+	result := Fit("gpt-4.1", s)
+
+	if len(result.Trimmed) < 2 {
+		t.Fatalf("expected at least 2 trimmed, got %v", result.Trimmed)
+	}
+	if !strings.Contains(result.Trimmed[0], "patterns") {
+		t.Errorf("expected patterns trimmed first, got %s", result.Trimmed[0])
+	}
+	if !strings.Contains(result.Trimmed[1], "conventions") {
+		t.Errorf("expected conventions trimmed second, got %s", result.Trimmed[1])
+	}
+}
+
+func TestFit_TruncatesDiff(t *testing.T) {
+	// Only diff is huge, no patterns/conventions
+	hugeDiff := strings.Repeat("z", 600_000) // ~150K tokens > 128K limit
+	s := Sections{
+		SystemBase: "base",
+		Diff:       hugeDiff,
+		UserMeta:   "meta",
+	}
+	result := Fit("gpt-4.1", s)
+
+	if len(result.Trimmed) == 0 {
+		t.Fatal("expected diff truncation")
+	}
+	if !strings.Contains(result.Trimmed[len(result.Trimmed)-1], "diff truncated") {
+		t.Errorf("expected diff truncation note, got %v", result.Trimmed)
+	}
+	if !strings.Contains(result.UserPrompt, "[diff truncated due to context limit]") {
+		t.Error("expected truncation marker in user prompt")
+	}
+}
+
+func TestFit_PreservesNoteInOutput(t *testing.T) {
+	big := strings.Repeat("w", 500_000)
+	s := Sections{
+		SystemBase: "base",
+		Patterns:   big,
+		Diff:       "small diff",
+		UserMeta:   "meta",
+	}
+	result := Fit("gpt-4.1", s)
+
+	if !strings.Contains(result.UserPrompt, "⚠️ Note: Context was trimmed") {
+		t.Error("expected trimming note in user prompt")
+	}
+}
+
+
+func TestFit_HugeUserMeta(t *testing.T) {
+	// UserMeta so large that base alone exceeds limit
+	// Use a unique marker past the truncation point
+	hugeDesc := strings.Repeat("d", 5000) + "UNIQUE_MARKER_PAST_TRUNCATION" + strings.Repeat("d", 595_000)
+	s := Sections{
+		SystemBase: "base",
+		Diff:       "small diff",
+		UserMeta:   hugeDesc,
+	}
+	result := Fit("gpt-4.1", s)
+
+	limit := LimitForModel("gpt-4.1") - reserveTokens
+	if result.EstTokens > limit {
+		t.Errorf("EstTokens %d exceeds limit %d", result.EstTokens, limit)
+	}
+	// Content past truncation point should not be present
+	if strings.Contains(result.UserPrompt, "UNIQUE_MARKER_PAST_TRUNCATION") {
+		t.Error("expected UserMeta to be truncated but found content past truncation point")
+	}
+	// Truncation marker should be present
+	if !strings.Contains(result.UserPrompt, "[description truncated]") {
+		t.Error("expected truncation marker in output")
+	}
+}
+
+func TestFit_NeverExceedsLimit(t *testing.T) {
+	// All sections huge — verify final tokens never exceed limit
+	big := strings.Repeat("a", 200_000)
+	s := Sections{
+		SystemBase:  strings.Repeat("s", 8000),
+		Patterns:    big,
+		Conventions: big,
+		FileContext: big,
+		Diff:        big,
+		UserMeta:    strings.Repeat("m", 8000),
+	}
+	result := Fit("gpt-4.1", s)
+
+	limit := LimitForModel("gpt-4.1") - reserveTokens
+	if result.EstTokens > limit {
+		t.Errorf("EstTokens %d exceeds limit %d (trimmed: %v)", result.EstTokens, limit, result.Trimmed)
+	}
+}

cmd/review-bot/main.go

@@ -10,6 +10,7 @@ import (
 	"strings"
 	"time"
 
+	"gitea.weiker.me/rodin/review-bot/budget"
 	"gitea.weiker.me/rodin/review-bot/gitea"
 	"gitea.weiker.me/rodin/review-bot/llm"
 	"gitea.weiker.me/rodin/review-bot/review"
@@ -18,6 +19,7 @@ import (
 var version = "dev"
 
 func main() {
+	versionFlag := flag.Bool("version", false, "Print version and exit")
 	// CLI flags
 	giteaURL := flag.String("gitea-url", envOrDefault("GITEA_URL", ""), "Gitea instance URL")
 	repo := flag.String("repo", envOrDefault("GITEA_REPO", ""), "Repository (owner/name)")
@@ -36,6 +38,13 @@ func main() {
 
 	flag.Parse()
 
+	if *versionFlag {
+		fmt.Printf("review-bot %s\n", version)
+		os.Exit(0)
+	}
+
+	log.Printf("review-bot %s", version)
+
 	// Validate required fields
 	if *giteaURL == "" || *repo == "" || *prNum == "" || *reviewerToken == "" ||
 		*llmBaseURL == "" || *llmAPIKey == "" || *llmModel == "" {
@@ -133,15 +142,26 @@ func main() {
 		log.Printf("Loaded patterns from %s (%d bytes)", *patternsRepo, len(patterns))
 	}
 
-	// Step 7: Build prompts
+	// Step 7: Budget-aware prompt assembly
-	systemPrompt := review.BuildSystemPrompt(conventions, patterns)
+	sections := budget.Sections{
-	userPrompt := review.BuildUserPrompt(pr.Title, pr.Body, diff, fileContext, ciPassed, ciDetails)
+		SystemBase:  review.BuildSystemBase(),
+		Patterns:    patterns,
+		Conventions: conventions,
+		FileContext: fileContext,
+		Diff:        diff,
+		UserMeta:    review.BuildUserMeta(pr.Title, pr.Body, ciPassed, ciDetails),
+	}
+	budgetResult := budget.Fit(*llmModel, sections)
+	log.Printf("Token estimate: ~%dK (limit: %dK)", budgetResult.EstTokens/1000, budget.LimitForModel(*llmModel)/1000)
+	if len(budgetResult.Trimmed) > 0 {
+		log.Printf("Context trimmed: %v", budgetResult.Trimmed)
+	}
 
 	// Step 8: Call LLM
 	log.Printf("Sending to LLM (%s)...", *llmModel)
 	messages := []llm.Message{
-		{Role: "system", Content: systemPrompt},
+		{Role: "system", Content: budgetResult.SystemPrompt},
-		{Role: "user", Content: userPrompt},
+		{Role: "user", Content: budgetResult.UserPrompt},
 	}
 
 	response, err := llmClient.Complete(ctx, messages)
@@ -235,12 +255,12 @@ func fetchPatterns(ctx context.Context, client *gitea.Client, patternsRepo, patt
 				continue
 			}
 
-			for filepath, content := range files {
+			for filePath, content := range files {
 				// Only include markdown and text files as patterns
-				if !isPatternFile(filepath) {
+				if !isPatternFile(filePath) {
 					continue
 				}
-				sb.WriteString(fmt.Sprintf("### %s/%s\n\n%s\n\n", repoRef, filepath, content))
+				sb.WriteString(fmt.Sprintf("### %s/%s\n\n%s\n\n", repoRef, filePath, content))
 			}
 		}
 	}

gitea/client.go

@@ -1,3 +1,6 @@
+// Package gitea provides a client for the Gitea API.
+// It supports pull request operations, file content retrieval,
+// and review submission.
 package gitea
 
 import (
@@ -8,6 +11,7 @@ import (
 	"io"
 	"log"
 	"net/http"
+	"net/url"
 	"strings"
 	"time"
 )
@@ -55,8 +59,8 @@ type ChangedFile struct {
 
 // GetPullRequest fetches PR metadata.
 func (c *Client) GetPullRequest(ctx context.Context, owner, repo string, number int) (*PullRequest, error) {
-	url := fmt.Sprintf("%s/api/v1/repos/%s/%s/pulls/%d", c.baseURL, owner, repo, number)
+	reqURL := fmt.Sprintf("%s/api/v1/repos/%s/%s/pulls/%d", c.baseURL, owner, repo, number)
-	body, err := c.doGet(ctx, url)
+	body, err := c.doGet(ctx, reqURL)
 	if err != nil {
 		return nil, fmt.Errorf("fetch PR: %w", err)
 	}
@@ -69,8 +73,8 @@ func (c *Client) GetPullRequest(ctx context.Context, owner, repo string, number
 
 // GetPullRequestDiff fetches the unified diff for a PR.
 func (c *Client) GetPullRequestDiff(ctx context.Context, owner, repo string, number int) (string, error) {
-	url := fmt.Sprintf("%s/api/v1/repos/%s/%s/pulls/%d.diff", c.baseURL, owner, repo, number)
+	reqURL := fmt.Sprintf("%s/api/v1/repos/%s/%s/pulls/%d.diff", c.baseURL, owner, repo, number)
-	body, err := c.doGet(ctx, url)
+	body, err := c.doGet(ctx, reqURL)
 	if err != nil {
 		return "", fmt.Errorf("fetch diff: %w", err)
 	}
@@ -79,8 +83,8 @@ func (c *Client) GetPullRequestDiff(ctx context.Context, owner, repo string, num
 
 // GetPullRequestFiles fetches the list of files changed in a PR.
 func (c *Client) GetPullRequestFiles(ctx context.Context, owner, repo string, number int) ([]ChangedFile, error) {
-	url := fmt.Sprintf("%s/api/v1/repos/%s/%s/pulls/%d/files", c.baseURL, owner, repo, number)
+	reqURL := fmt.Sprintf("%s/api/v1/repos/%s/%s/pulls/%d/files", c.baseURL, owner, repo, number)
-	body, err := c.doGet(ctx, url)
+	body, err := c.doGet(ctx, reqURL)
 	if err != nil {
 		return nil, fmt.Errorf("fetch PR files: %w", err)
 	}
@@ -93,8 +97,8 @@ func (c *Client) GetPullRequestFiles(ctx context.Context, owner, repo string, nu
 
 // GetCommitStatuses fetches CI statuses for a commit SHA.
 func (c *Client) GetCommitStatuses(ctx context.Context, owner, repo, sha string) ([]CommitStatus, error) {
-	url := fmt.Sprintf("%s/api/v1/repos/%s/%s/commits/%s/statuses", c.baseURL, owner, repo, sha)
+	reqURL := fmt.Sprintf("%s/api/v1/repos/%s/%s/commits/%s/statuses", c.baseURL, owner, repo, sha)
-	body, err := c.doGet(ctx, url)
+	body, err := c.doGet(ctx, reqURL)
 	if err != nil {
 		return nil, fmt.Errorf("fetch commit statuses: %w", err)
 	}
@@ -107,8 +111,8 @@ func (c *Client) GetCommitStatuses(ctx context.Context, owner, repo, sha string)
 
 // GetFileContent fetches a file from the default branch of a repo.
 func (c *Client) GetFileContent(ctx context.Context, owner, repo, filepath string) (string, error) {
-	url := fmt.Sprintf("%s/api/v1/repos/%s/%s/raw/%s", c.baseURL, owner, repo, filepath)
+	reqURL := fmt.Sprintf("%s/api/v1/repos/%s/%s/raw/%s", c.baseURL, owner, repo, escapePath(filepath))
-	body, err := c.doGet(ctx, url)
+	body, err := c.doGet(ctx, reqURL)
 	if err != nil {
 		return "", fmt.Errorf("fetch file %s: %w", filepath, err)
 	}
@@ -117,8 +121,8 @@ func (c *Client) GetFileContent(ctx context.Context, owner, repo, filepath strin
 
 // GetFileContentRef fetches a file from a specific ref (branch/tag/sha) in a repo.
 func (c *Client) GetFileContentRef(ctx context.Context, owner, repo, filepath, ref string) (string, error) {
-	url := fmt.Sprintf("%s/api/v1/repos/%s/%s/raw/%s?ref=%s", c.baseURL, owner, repo, filepath, ref)
+	reqURL := fmt.Sprintf("%s/api/v1/repos/%s/%s/raw/%s?ref=%s", c.baseURL, owner, repo, escapePath(filepath), url.QueryEscape(ref))
-	body, err := c.doGet(ctx, url)
+	body, err := c.doGet(ctx, reqURL)
 	if err != nil {
 		return "", fmt.Errorf("fetch file %s@%s: %w", filepath, ref, err)
 	}
@@ -128,7 +132,7 @@ func (c *Client) GetFileContentRef(ctx context.Context, owner, repo, filepath, r
 // PostReview submits a review to a PR.
 // event should be "APPROVED" or "REQUEST_CHANGES".
 func (c *Client) PostReview(ctx context.Context, owner, repo string, number int, event, body string) error {
-	url := fmt.Sprintf("%s/api/v1/repos/%s/%s/pulls/%d/reviews", c.baseURL, owner, repo, number)
+	reqURL := fmt.Sprintf("%s/api/v1/repos/%s/%s/pulls/%d/reviews", c.baseURL, owner, repo, number)
 
 	payload := struct {
 		Body  string `json:"body"`
@@ -143,7 +147,7 @@ func (c *Client) PostReview(ctx context.Context, owner, repo string, number int,
 		return fmt.Errorf("marshal review payload: %w", err)
 	}
 
-	req, err := http.NewRequestWithContext(ctx, "POST", url, bytes.NewReader(data))
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, reqURL, bytes.NewReader(data))
 	if err != nil {
 		return fmt.Errorf("create review request: %w", err)
 	}
@@ -163,8 +167,8 @@ func (c *Client) PostReview(ctx context.Context, owner, repo string, number int,
 	return nil
 }
 
-func (c *Client) doGet(ctx context.Context, url string) ([]byte, error) {
+func (c *Client) doGet(ctx context.Context, reqURL string) ([]byte, error) {
-	req, err := http.NewRequestWithContext(ctx, "GET", url, nil)
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, reqURL, nil)
 	if err != nil {
 		return nil, err
 	}
@@ -183,6 +187,18 @@ func (c *Client) doGet(ctx context.Context, url string) ([]byte, error) {
 	return io.ReadAll(resp.Body)
 }
 
+// escapePath escapes each segment of a relative file path for use in URLs.
+// Slashes are preserved as path separators; other special characters are escaped.
+// Input should be a relative path (no leading slash). Already-encoded segments
+// will be double-encoded, which is the desired behavior for user-provided paths.
+func escapePath(p string) string {
+	parts := strings.Split(p, "/")
+	for i, part := range parts {
+		parts[i] = url.PathEscape(part)
+	}
+	return strings.Join(parts, "/")
+}
+
 // ContentEntry represents a file or directory entry from the contents API.
 type ContentEntry struct {
 	Name string `json:"name"`
@@ -191,9 +207,15 @@ type ContentEntry struct {
 }
 
 // ListContents lists files and directories at a given path in a repo.
+// Pass an empty path to list the repository root.
 func (c *Client) ListContents(ctx context.Context, owner, repo, path string) ([]ContentEntry, error) {
-	url := fmt.Sprintf("%s/api/v1/repos/%s/%s/contents/%s", c.baseURL, owner, repo, path)
+	var reqURL string
-	body, err := c.doGet(ctx, url)
+	if path == "" {
+		reqURL = fmt.Sprintf("%s/api/v1/repos/%s/%s/contents", c.baseURL, owner, repo)
+	} else {
+		reqURL = fmt.Sprintf("%s/api/v1/repos/%s/%s/contents/%s", c.baseURL, owner, repo, escapePath(path))
+	}
+	body, err := c.doGet(ctx, reqURL)
 	if err != nil {
 		return nil, fmt.Errorf("list contents %s: %w", path, err)
 	}

gitea/client_test.go

@@ -294,3 +294,27 @@ func TestGetAllFilesInPath_File(t *testing.T) {
 		t.Errorf("unexpected content: %q", files["README.md"])
 	}
 }
+
+func TestEscapePath(t *testing.T) {
+	tests := []struct {
+		name  string
+		input string
+		want  string
+	}{
+		{"simple", "src/main.go", "src/main.go"},
+		{"spaces", "my dir/my file.go", "my%20dir/my%20file.go"},
+		{"special chars", "path/file#1.txt", "path/file%231.txt"},
+		{"empty", "", ""},
+		{"single segment", "README.md", "README.md"},
+		{"nested deep", "a/b/c/d.md", "a/b/c/d.md"},
+		{"already encoded", "path/file%20name.go", "path/file%2520name.go"},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := escapePath(tt.input)
+			if got != tt.want {
+				t.Errorf("escapePath(%q) = %q, want %q", tt.input, got, tt.want)
+			}
+		})
+	}
+}

llm/client.go

@@ -1,3 +1,4 @@
+// Package llm provides a client for OpenAI-compatible chat completion APIs.
 package llm
 
 import (

review/prompt.go

@@ -1,3 +1,5 @@
+// Package review builds prompts for AI code review and parses LLM responses
+// into structured review results.
 package review
 
 import (
@@ -5,8 +7,10 @@ import (
 	"strings"
 )
 
-// BuildSystemPrompt constructs the system prompt for the LLM reviewer.
+// BuildSystemBase returns the core system prompt instructions without
-func BuildSystemPrompt(conventions, patterns string) string {
+// patterns or conventions. Used by the budget package to separate
+// trimmable from non-trimmable content.
+func BuildSystemBase() string {
 	var sb strings.Builder
 
 	sb.WriteString("You are an expert code reviewer. Review the provided pull request diff carefully.\n\n")
@@ -40,6 +44,15 @@ func BuildSystemPrompt(conventions, patterns string) string {
 	sb.WriteString("- Line numbers should reference the new file line numbers from the diff headers.\n")
 	sb.WriteString("- If the diff is empty or trivial (only formatting/whitespace), APPROVE with no findings.\n")
 
+	return sb.String()
+}
+
+// BuildSystemPrompt constructs the full system prompt with patterns and conventions.
+// Deprecated: Use BuildSystemBase with budget.Fit for context-aware assembly.
+func BuildSystemPrompt(conventions, patterns string) string {
+	var sb strings.Builder
+	sb.WriteString(BuildSystemBase())
+
 	if patterns != "" {
 		sb.WriteString(fmt.Sprintf("\n\n## Language Patterns & Idioms\n\nUse the following patterns as review criteria. Code that violates these established patterns is a finding:\n\n%s\n", patterns))
 	}
@@ -51,8 +64,9 @@ func BuildSystemPrompt(conventions, patterns string) string {
 	return sb.String()
 }
 
-// BuildUserPrompt constructs the user message with PR context.
+// BuildUserMeta returns the PR metadata header (title, description, CI status)
-func BuildUserPrompt(title, description, diff, fileContext string, ciPassed bool, ciDetails string) string {
+// without the diff or file context. Used by the budget package.
+func BuildUserMeta(title, description string, ciPassed bool, ciDetails string) string {
 	var sb strings.Builder
 
 	sb.WriteString(fmt.Sprintf("## Pull Request: %s\n\n", title))
@@ -71,6 +85,16 @@ func BuildUserPrompt(title, description, diff, fileContext string, ciPassed bool
 		sb.WriteString(fmt.Sprintf("CI Details: %s\n", ciDetails))
 	}
 
+	return sb.String()
+}
+
+// BuildUserPrompt constructs the user message with PR context.
+// Deprecated: Use BuildUserMeta with budget.Fit for context-aware assembly.
+func BuildUserPrompt(title, description, diff, fileContext string, ciPassed bool, ciDetails string) string {
+	var sb strings.Builder
+
+	sb.WriteString(BuildUserMeta(title, description, ciPassed, ciDetails))
+
 	if fileContext != "" {
 		sb.WriteString("\n### Full File Context (modified files)\n\n")
 		sb.WriteString(fileContext)

review/prompt_test.go

@@ -116,3 +116,43 @@ func TestBuildUserPrompt_WithoutFileContext(t *testing.T) {
 		t.Error("should not include file context section when empty")
 	}
 }
+
+
+func TestBuildSystemBase(t *testing.T) {
+	result := BuildSystemBase()
+	if result == "" {
+		t.Fatal("BuildSystemBase returned empty string")
+	}
+	if !strings.Contains(result, "expert code reviewer") {
+		t.Error("expected reviewer role in system base")
+	}
+	if !strings.Contains(result, "REQUEST_CHANGES") {
+		t.Error("expected verdict format in system base")
+	}
+	if !strings.Contains(result, "JSON") {
+		t.Error("expected JSON output instruction in system base")
+	}
+}
+
+func TestBuildUserMeta(t *testing.T) {
+	result := BuildUserMeta("Fix bug", "Some description", true, "all checks passed")
+	if !strings.Contains(result, "Fix bug") {
+		t.Error("expected title in user meta")
+	}
+	if !strings.Contains(result, "Some description") {
+		t.Error("expected description in user meta")
+	}
+	if !strings.Contains(result, "PASSED") {
+		t.Error("expected CI PASSED status")
+	}
+}
+
+func TestBuildUserMeta_CIFailed(t *testing.T) {
+	result := BuildUserMeta("Title", "", false, "test job failed")
+	if !strings.Contains(result, "FAILED") {
+		t.Error("expected CI FAILED status")
+	}
+	if strings.Contains(result, "Description") {
+		t.Error("expected no description section when empty")
+	}
+}