feat: add GetChangedFiles() method to Gitea client for PR file diffs

Add ChangedFile type and GetChangedFiles() method that calls the Gitea
API endpoint GET /repos/{owner}/{repo}/pulls/{index}/files to retrieve
the list of files changed in a pull request. This is a prerequisite for
displaying changed files in the PR detail view (#189).

Includes unit tests for success and error cases.

Closes leeworks-agents/gitea-mobile#205

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.air.toml

@@ -0,0 +1,44 @@
+root = "."
+testdata_dir = "testdata"
+tmp_dir = "tmp"
+
+[build]
+  args_bin = []
+  bin = "./tmp/main"
+  cmd = "go build -o ./tmp/main ./cmd/server"
+  delay = 500
+  exclude_dir = ["assets", "tmp", "vendor", "testdata", ".git", "node_modules"]
+  exclude_file = []
+  exclude_regex = ["_test\\.go$"]
+  exclude_unchanged = false
+  follow_symlink = false
+  full_bin = ""
+  include_dir = []
+  include_ext = ["go", "html", "css", "js"]
+  include_file = []
+  kill_delay = "0s"
+  log = "build-errors.log"
+  poll = false
+  poll_interval = 0
+  rerun = false
+  rerun_delay = 500
+  send_interrupt = false
+  stop_on_error = false
+
+[color]
+  app = ""
+  build = "yellow"
+  main = "magenta"
+  runner = "green"
+  watcher = "cyan"
+
+[log]
+  main_only = false
+  time = false
+
+[misc]
+  clean_on_exit = true
+
+[screen]
+  clear_on_rebuild = false
+  keep_scroll = true

.gitea/workflows/build.yaml

@@ -15,6 +15,9 @@ jobs:
         with:
           go-version: '1.22'
 
+      - name: Vet
+        run: go vet ./...
+
       - name: Run tests
         run: go test -race ./...
 

README.md

@@ -0,0 +1,116 @@
+# Gitea Mobile
+
+A mobile-first Progressive Web App (PWA) for managing Gitea issues and pull requests across multiple repositories and organizations from an iPhone. Built with Go, HTMX, and hand-rolled CSS -- no JavaScript frameworks, no build step, no node_modules.
+
+## Tech Stack
+
+| Layer | Choice |
+|-------|--------|
+| Backend | Go + Gitea SDK (`code.gitea.io/sdk/gitea`) |
+| Frontend | HTMX + Go `html/template` + hand-rolled CSS |
+| Container | Multi-stage Dockerfile -> distroless (~15MB) |
+| Deployment | Kustomize manifests + FluxCD GitOps |
+
+## Project Structure
+
+```
+/
+├── cmd/server/main.go          # entrypoint
+├── internal/
+│   ├── config/config.go        # env-based configuration
+│   ├── gitea/client.go         # Gitea SDK wrapper / aggregation layer
+│   ├── handlers/               # HTTP handlers (issues, PRs, triage, settings)
+│   ├── auth/                   # cookie-based token auth
+│   ├── middleware/              # auth middleware, logging
+│   └── templates/              # Go html/template files (for HTMX)
+├── static/                     # CSS, JS (htmx.min.js), icons, manifest
+├── .gitea/workflows/build.yaml # CI pipeline (Gitea Actions)
+├── Dockerfile
+├── flake.nix                   # Nix dev shell with Go + air
+└── go.mod
+```
+
+## Local Development
+
+### Prerequisites
+
+- [Nix](https://nixos.org/download/) with flakes enabled, **or** Go 1.22+
+- A Gitea instance with an API token
+
+### Quick Start
+
+```bash
+# Enter the Nix dev shell (provides Go, gopls, air)
+nix develop
+
+# Set required environment variables
+export GITEA_URL=https://gitea.leeworks.dev
+export SESSION_SECRET=$(openssl rand -hex 32)
+
+# Optional: set a default API token
+export GITEA_TOKEN=your-gitea-api-token
+
+# Start the server with live reload
+air
+```
+
+If you are not using Nix, install Go 1.22+ and [air](https://github.com/air-verse/air) manually, then run the same commands above starting from the export lines.
+
+### Environment Variables
+
+| Variable | Required | Default | Description |
+|----------|----------|---------|-------------|
+| `GITEA_URL` | Yes | -- | Base URL of the Gitea instance |
+| `SESSION_SECRET` | Yes | -- | HMAC key for signing session cookies (min 32 chars) |
+| `GITEA_TOKEN` | No | -- | Default API token (users can set their own via the settings page) |
+| `LISTEN_ADDR` | No | `:8080` | Server listen address |
+
+### Live Reload with Air
+
+The dev shell includes [air](https://github.com/air-verse/air) for automatic recompilation on file changes. Configuration is in `.air.toml`. Air watches `.go` and `.html` files under `cmd/`, `internal/`, and `static/` and rebuilds/restarts the server automatically.
+
+## Running Tests
+
+```bash
+# Run all tests
+go test ./...
+
+# Run tests with race detection
+go test -race ./...
+```
+
+## Building the Container
+
+```bash
+# Build the Docker image
+docker build -t gitea-mobile .
+
+# Run locally
+docker run -p 8080:8080 \
+  -e GITEA_URL=https://gitea.leeworks.dev \
+  -e SESSION_SECRET=$(openssl rand -hex 32) \
+  gitea-mobile
+```
+
+The Dockerfile uses a multi-stage build: Go binary compiled in an Alpine builder stage, then copied into a distroless image (~15MB final size).
+
+## Deployment
+
+Kubernetes manifests for this app live in the Talos cluster repo under `testing1/first-cluster/apps/gitea-mobile/`. FluxCD syncs from that repo and handles automated image updates via `ImagePolicy` annotations.
+
+Key deployment resources:
+- `deployment.yaml` -- Pod spec with health checks
+- `service.yaml` -- ClusterIP service on port 8080
+- `ingressroute.yaml` -- Traefik IngressRoute for `gitea-mobile.testing.leeworks.dev`
+- `kustomization.yaml` -- Kustomize overlay
+
+## Contributing
+
+1. Fork the repository
+2. Create a feature branch: `git checkout -b feature/your-feature`
+3. Make your changes and add tests
+4. Run `go test -race ./...` to verify
+5. Commit with a clear message referencing the issue number
+6. Push to your fork and open a pull request
+
+All PRs target the fork (`leeworks-agents/gitea-mobile`), not the upstream repo.

SMOKE_TEST.md

@@ -0,0 +1,148 @@
+# Post-Deployment Smoke Test Runbook
+
+Smoke test procedure for verifying gitea-mobile after deployment to the Talos cluster.
+
+## Pre-conditions
+
+Before running the smoke test, confirm:
+
+- [ ] FluxCD has reconciled the latest manifests: `flux get kustomizations -n flux-system`
+- [ ] The gitea-mobile pod is Running: `kubectl get pods -n gitea-mobile`
+- [ ] The IngressRoute is active: `kubectl get ingressroute -n gitea-mobile`
+- [ ] DNS resolves `gitea-mobile.testing.leeworks.dev` to the cluster ingress
+
+## Step 1: Pod Health
+
+```bash
+# Verify the pod is running and ready
+kubectl get pods -n gitea-mobile
+# Expected: STATUS=Running, READY=1/1
+
+# Check pod logs for startup errors
+kubectl logs -n gitea-mobile deployment/gitea-mobile --tail=20
+# Expected: JSON log line with "server starting" message
+```
+
+## Step 2: Health Endpoint
+
+```bash
+# Hit the health check endpoint from inside the cluster
+kubectl exec -n gitea-mobile deployment/gitea-mobile -- wget -qO- http://localhost:8080/health
+# Expected: HTTP 200
+
+# Hit the health check endpoint from outside the cluster
+curl -s -o /dev/null -w "%{http_code}" https://gitea-mobile.testing.leeworks.dev/health
+# Expected: 200
+```
+
+## Step 3: TLS and Ingress
+
+```bash
+# Verify TLS certificate is valid
+curl -vI https://gitea-mobile.testing.leeworks.dev 2>&1 | grep "SSL certificate"
+# Expected: valid certificate from Let's Encrypt or cluster CA
+
+# Verify the app responds with HTML
+curl -s https://gitea-mobile.testing.leeworks.dev | head -5
+# Expected: HTML document with <html> tag
+```
+
+## Step 4: Authentication Flow
+
+1. Open `https://gitea-mobile.testing.leeworks.dev` in a browser
+2. Navigate to the Settings page (`/settings`)
+3. Enter a valid Gitea API token
+4. Submit the form
+5. **Expected**: Token is saved, page confirms success
+6. Navigate back to the Issues tab
+7. **Expected**: Issues load from the Gitea API using the saved token
+
+## Step 5: Core Functionality -- Issues
+
+1. Navigate to the Issues tab (`/issues`)
+2. **Expected**: Cross-org issues load and display with titles, labels, and timestamps
+3. Tap on an issue to expand details
+4. **Expected**: Issue body renders correctly
+5. Use the filter dropdown to filter by repo or label
+6. **Expected**: List updates via HTMX without full page reload
+
+## Step 6: Core Functionality -- Pull Requests
+
+1. Navigate to the PRs tab (`/pulls`)
+2. **Expected**: Pull requests load with review status icons
+3. Tap on a PR to see details
+4. **Expected**: PR diff summary or review status displays correctly
+
+## Step 7: Core Functionality -- Dashboard / Triage Queue
+
+1. Navigate to the Dashboard/Triage tab (`/`)
+2. **Expected**: Unassigned issues and PRs awaiting review appear sorted by priority
+
+## Step 8: Create Issue (Write Operation)
+
+1. Navigate to the new issue form
+2. Fill in title: `[smoke-test] Automated verification`
+3. Fill in body: `This issue was created during smoke testing. Safe to close.`
+4. Submit the form
+5. **Expected**: Issue is created successfully in Gitea
+6. Verify in Gitea web UI that the issue exists
+7. Close and delete the test issue after verification
+
+## Step 9: Apply Label (Write Operation)
+
+1. On any test issue, attempt to apply a label
+2. **Expected**: Label is applied via the Gitea API and reflected in the UI
+
+## Step 10: PWA / iPhone Safari
+
+1. Open `https://gitea-mobile.testing.leeworks.dev` on iPhone Safari
+2. **Expected**: App loads with mobile-optimized layout, no horizontal scroll
+3. Tap "Add to Home Screen" from the Safari share menu
+4. **Expected**: App icon appears on the home screen (apple-touch-icon)
+5. Launch from the home screen
+6. **Expected**: App opens in standalone mode (no Safari browser chrome)
+7. Verify bottom navigation does not overlap with iPhone home indicator
+8. Toggle device dark mode in Settings
+9. **Expected**: App switches between dark and light themes via `prefers-color-scheme`
+10. See issue #93 for the full PWA validation checklist
+
+## Expected Results Summary
+
+| Step | Check | Expected |
+|------|-------|----------|
+| 1 | Pod status | Running, Ready 1/1 |
+| 2 | `/health` | HTTP 200 |
+| 3 | TLS | Valid cert, HTML response |
+| 4 | Auth | Token saved, API calls work |
+| 5 | Issues | List loads, filter works |
+| 6 | PRs | List loads with review status |
+| 7 | Dashboard/Triage | Queue displays correctly at `/` |
+| 8 | Create issue | Issue created in Gitea |
+| 9 | Apply label | Label applied via API |
+| 10 | PWA | Standalone mode, safe areas, dark mode |
+
+## Rollback Procedure
+
+If the deployment is broken or the app is not functioning:
+
+```bash
+# Roll back to the previous deployment revision
+kubectl rollout undo deployment/gitea-mobile -n gitea-mobile
+
+# Verify the rollback
+kubectl rollout status deployment/gitea-mobile -n gitea-mobile
+# Expected: "deployment successfully rolled out"
+
+# Check that the previous image tag is running
+kubectl get deployment gitea-mobile -n gitea-mobile -o jsonpath='{.spec.template.spec.containers[0].image}'
+```
+
+If FluxCD keeps reconciling back to the broken version, suspend reconciliation temporarily:
+
+```bash
+# Suspend Flux reconciliation
+flux suspend kustomization gitea-mobile -n flux-system
+
+# After fixing the issue, resume
+flux resume kustomization gitea-mobile -n flux-system
+```

internal/gitea/client.go

@@ -8,8 +8,11 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
+	"log/slog"
+	"math"
 	"net/http"
 	"sort"
+	"strconv"
 	"strings"
 	"sync"
 	"time"
@@ -27,6 +30,11 @@ type Client struct {
 	maxConcurrent int
 	// cacheTTL controls how long cache entries remain valid.
 	cacheTTL time.Duration
+
+	// maxRetries is the maximum number of retries for rate-limited requests.
+	maxRetries int
+	// baseRetryDelay is the initial backoff delay before the first retry.
+	baseRetryDelay time.Duration
 }
 
 type cacheEntry struct {
@@ -129,39 +137,102 @@ func NewClient(baseURL string) *Client {
 		httpClient: &http.Client{
 			Timeout: 30 * time.Second,
 		},
-		cache:         make(map[string]*cacheEntry),
+		cache:          make(map[string]*cacheEntry),
-		maxConcurrent: 5,
+		maxConcurrent:  5,
-		cacheTTL:      30 * time.Second,
+		cacheTTL:       30 * time.Second,
+		maxRetries:     3,
+		baseRetryDelay: 1 * time.Second,
 	}
 }
 
 // doRequest performs an authenticated HTTP request to the Gitea API.
+// It automatically retries on HTTP 429 (rate limit) responses with
+// exponential backoff, respecting the Retry-After header when present.
 func (c *Client) doRequest(ctx context.Context, token, method, path string, body io.Reader) (*http.Response, error) {
 	url := c.baseURL + "/api/v1" + path
 
-	req, err := http.NewRequestWithContext(ctx, method, url, body)
+	// Read the body once so we can replay it on retries.
-	if err != nil {
+	var bodyBytes []byte
-		return nil, fmt.Errorf("creating request: %w", err)
-	}
-
-	req.Header.Set("Authorization", "token "+token)
-	req.Header.Set("Accept", "application/json")
 	if body != nil {
-		req.Header.Set("Content-Type", "application/json")
+		var err error
+		bodyBytes, err = io.ReadAll(body)
+		if err != nil {
+			return nil, fmt.Errorf("reading request body: %w", err)
+		}
 	}
 
-	resp, err := c.httpClient.Do(req)
+	var lastErr error
-	if err != nil {
+	for attempt := 0; attempt <= c.maxRetries; attempt++ {
-		return nil, fmt.Errorf("executing request: %w", err)
+		// Recreate the body reader for each attempt.
+		var reqBody io.Reader
+		if bodyBytes != nil {
+			reqBody = strings.NewReader(string(bodyBytes))
+		}
+
+		req, err := http.NewRequestWithContext(ctx, method, url, reqBody)
+		if err != nil {
+			return nil, fmt.Errorf("creating request: %w", err)
+		}
+
+		req.Header.Set("Authorization", "token "+token)
+		req.Header.Set("Accept", "application/json")
+		if bodyBytes != nil {
+			req.Header.Set("Content-Type", "application/json")
+		}
+
+		resp, err := c.httpClient.Do(req)
+		if err != nil {
+			return nil, fmt.Errorf("executing request: %w", err)
+		}
+
+		// Not rate-limited: handle normally.
+		if resp.StatusCode != http.StatusTooManyRequests {
+			if resp.StatusCode >= 400 {
+				defer resp.Body.Close()
+				respBody, _ := io.ReadAll(resp.Body)
+				return nil, fmt.Errorf("API error %d: %s", resp.StatusCode, string(respBody))
+			}
+			return resp, nil
+		}
+
+		// Rate-limited (429): close body and compute retry delay.
+		resp.Body.Close()
+
+		if attempt == c.maxRetries {
+			lastErr = fmt.Errorf("API rate limit exceeded after %d retries (429)", c.maxRetries)
+			break
+		}
+
+		delay := c.retryDelay(resp, attempt)
+		slog.Warn("rate limited by Gitea API, retrying",
+			"attempt", attempt+1,
+			"max_retries", c.maxRetries,
+			"delay", delay,
+			"path", path,
+		)
+
+		select {
+		case <-ctx.Done():
+			return nil, ctx.Err()
+		case <-time.After(delay):
+			// Continue to next attempt.
+		}
 	}
 
-	if resp.StatusCode >= 400 {
+	return nil, lastErr
-		defer resp.Body.Close()
+}
-		respBody, _ := io.ReadAll(resp.Body)
-		return nil, fmt.Errorf("API error %d: %s", resp.StatusCode, string(respBody))
-	}
 
-	return resp, nil
+// retryDelay computes the delay before the next retry attempt. It uses the
+// Retry-After header value (in seconds) if present, otherwise falls back to
+// exponential backoff: baseRetryDelay * 2^attempt.
+func (c *Client) retryDelay(resp *http.Response, attempt int) time.Duration {
+	if ra := resp.Header.Get("Retry-After"); ra != "" {
+		if seconds, err := strconv.Atoi(ra); err == nil && seconds > 0 {
+			return time.Duration(seconds) * time.Second
+		}
+	}
+	// Exponential backoff: 1s, 2s, 4s, ...
+	return c.baseRetryDelay * time.Duration(math.Pow(2, float64(attempt)))
 }
 
 // getFromCache returns cached data if still valid.
@@ -689,6 +760,33 @@ func (c *Client) GetPull(ctx context.Context, token, owner, repo string, index i
 	return &pr, nil
 }
 
+// ChangedFile represents a file changed in a pull request.
+type ChangedFile struct {
+	Filename    string `json:"filename"`
+	Status      string `json:"status"` // "added", "modified", "removed", "renamed"
+	Additions   int    `json:"additions"`
+	Deletions   int    `json:"deletions"`
+	Changes     int    `json:"changes"`
+	PreviousFilename string `json:"previous_filename,omitempty"`
+}
+
+// GetChangedFiles fetches the list of files changed in a pull request.
+func (c *Client) GetChangedFiles(ctx context.Context, token, owner, repo string, index int64) ([]ChangedFile, error) {
+	path := fmt.Sprintf("/repos/%s/%s/pulls/%d/files?limit=50", owner, repo, index)
+	resp, err := c.doRequest(ctx, token, http.MethodGet, path, nil)
+	if err != nil {
+		return nil, fmt.Errorf("fetching changed files: %w", err)
+	}
+	defer resp.Body.Close()
+
+	var files []ChangedFile
+	if err := json.NewDecoder(resp.Body).Decode(&files); err != nil {
+		return nil, fmt.Errorf("decoding changed files: %w", err)
+	}
+
+	return files, nil
+}
+
 // GetIssueComments fetches comments for an issue or pull request.
 func (c *Client) GetIssueComments(ctx context.Context, token, owner, repo string, index int64) ([]Comment, error) {
 	path := fmt.Sprintf("/repos/%s/%s/issues/%d/comments?limit=50", owner, repo, index)

internal/gitea/client_test.go

@@ -1298,3 +1298,221 @@ func TestListAllPullRequests_Pagination(t *testing.T) {
 		t.Error("page 2: HasMore should be false")
 	}
 }
+
+func TestDoRequest_RateLimitRetry(t *testing.T) {
+	attempts := 0
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		attempts++
+		if attempts <= 2 {
+			w.Header().Set("Retry-After", "0")
+			w.WriteHeader(http.StatusTooManyRequests)
+			return
+		}
+		w.WriteHeader(http.StatusOK)
+		fmt.Fprint(w, `[{"username":"test-org"}]`)
+	}))
+	defer srv.Close()
+
+	c := NewClient(srv.URL)
+	c.maxRetries = 3
+	c.baseRetryDelay = 1 * time.Millisecond // Fast for tests.
+
+	resp, err := c.doRequest(context.Background(), "test-token", "GET", "/user/orgs", nil)
+	if err != nil {
+		t.Fatalf("expected success after retries, got: %v", err)
+	}
+	resp.Body.Close()
+
+	if attempts != 3 {
+		t.Errorf("expected 3 attempts, got %d", attempts)
+	}
+}
+
+func TestDoRequest_RateLimitExhausted(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusTooManyRequests)
+	}))
+	defer srv.Close()
+
+	c := NewClient(srv.URL)
+	c.maxRetries = 2
+	c.baseRetryDelay = 1 * time.Millisecond
+
+	_, err := c.doRequest(context.Background(), "test-token", "GET", "/user/orgs", nil)
+	if err == nil {
+		t.Fatal("expected error after exhausting retries")
+	}
+	if !strings.Contains(err.Error(), "rate limit exceeded") {
+		t.Errorf("expected rate limit error, got: %v", err)
+	}
+}
+
+func TestDoRequest_RateLimitWithRetryAfterHeader(t *testing.T) {
+	attempts := 0
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		attempts++
+		if attempts == 1 {
+			w.Header().Set("Retry-After", "1")
+			w.WriteHeader(http.StatusTooManyRequests)
+			return
+		}
+		w.WriteHeader(http.StatusOK)
+		fmt.Fprint(w, `[]`)
+	}))
+	defer srv.Close()
+
+	c := NewClient(srv.URL)
+	c.maxRetries = 3
+	c.baseRetryDelay = 1 * time.Millisecond
+
+	start := time.Now()
+	resp, err := c.doRequest(context.Background(), "test-token", "GET", "/user/orgs", nil)
+	elapsed := time.Since(start)
+	if err != nil {
+		t.Fatalf("expected success, got: %v", err)
+	}
+	resp.Body.Close()
+
+	// Retry-After: 1 means 1 second delay.
+	if elapsed < 900*time.Millisecond {
+		t.Errorf("expected at least ~1s delay from Retry-After header, got %v", elapsed)
+	}
+}
+
+func TestDoRequest_RateLimitCancelledContext(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Retry-After", "60")
+		w.WriteHeader(http.StatusTooManyRequests)
+	}))
+	defer srv.Close()
+
+	c := NewClient(srv.URL)
+	c.maxRetries = 3
+	c.baseRetryDelay = 1 * time.Millisecond
+
+	ctx, cancel := context.WithTimeout(context.Background(), 50*time.Millisecond)
+	defer cancel()
+
+	_, err := c.doRequest(ctx, "test-token", "GET", "/user/orgs", nil)
+	if err == nil {
+		t.Fatal("expected error from cancelled context")
+	}
+}
+
+func TestDoRequest_NonRateLimitErrorNotRetried(t *testing.T) {
+	attempts := 0
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		attempts++
+		w.WriteHeader(http.StatusForbidden)
+		fmt.Fprint(w, `{"message":"forbidden"}`)
+	}))
+	defer srv.Close()
+
+	c := NewClient(srv.URL)
+	c.maxRetries = 3
+	c.baseRetryDelay = 1 * time.Millisecond
+
+	_, err := c.doRequest(context.Background(), "test-token", "GET", "/user/orgs", nil)
+	if err == nil {
+		t.Fatal("expected error for 403")
+	}
+	if attempts != 1 {
+		t.Errorf("expected only 1 attempt for non-429 error, got %d", attempts)
+	}
+}
+
+func TestRetryDelay_WithRetryAfterHeader(t *testing.T) {
+	c := NewClient("https://example.com")
+	c.baseRetryDelay = 1 * time.Second
+
+	resp := &http.Response{Header: http.Header{}}
+	resp.Header.Set("Retry-After", "5")
+
+	delay := c.retryDelay(resp, 0)
+	if delay != 5*time.Second {
+		t.Errorf("expected 5s from Retry-After, got %v", delay)
+	}
+}
+
+func TestRetryDelay_ExponentialBackoff(t *testing.T) {
+	c := NewClient("https://example.com")
+	c.baseRetryDelay = 1 * time.Second
+
+	resp := &http.Response{Header: http.Header{}}
+
+	tests := []struct {
+		attempt int
+		want    time.Duration
+	}{
+		{0, 1 * time.Second},
+		{1, 2 * time.Second},
+		{2, 4 * time.Second},
+	}
+
+	for _, tt := range tests {
+		delay := c.retryDelay(resp, tt.attempt)
+		if delay != tt.want {
+			t.Errorf("attempt %d: got %v, want %v", tt.attempt, delay, tt.want)
+		}
+	}
+}
+
+func TestGetChangedFiles(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.Method != http.MethodGet {
+			t.Errorf("expected GET, got %s", r.Method)
+		}
+		if r.URL.Path != "/api/v1/repos/owner1/repo1/pulls/5/files" {
+			t.Errorf("unexpected path: %s", r.URL.Path)
+		}
+		if r.Header.Get("Authorization") != "token test-token" {
+			t.Error("missing or wrong Authorization header")
+		}
+
+		files := []ChangedFile{
+			{Filename: "main.go", Status: "modified", Additions: 10, Deletions: 3, Changes: 13},
+			{Filename: "new_file.go", Status: "added", Additions: 25, Deletions: 0, Changes: 25},
+			{Filename: "old_file.go", Status: "removed", Additions: 0, Deletions: 15, Changes: 15},
+		}
+		json.NewEncoder(w).Encode(files)
+	}))
+	defer server.Close()
+
+	c := NewClient(server.URL)
+	files, err := c.GetChangedFiles(context.Background(), "test-token", "owner1", "repo1", 5)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if len(files) != 3 {
+		t.Fatalf("got %d files, want 3", len(files))
+	}
+	if files[0].Filename != "main.go" {
+		t.Errorf("files[0].Filename = %q, want %q", files[0].Filename, "main.go")
+	}
+	if files[0].Status != "modified" {
+		t.Errorf("files[0].Status = %q, want %q", files[0].Status, "modified")
+	}
+	if files[1].Status != "added" {
+		t.Errorf("files[1].Status = %q, want %q", files[1].Status, "added")
+	}
+	if files[2].Status != "removed" {
+		t.Errorf("files[2].Status = %q, want %q", files[2].Status, "removed")
+	}
+}
+
+func TestGetChangedFiles_Error(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusNotFound)
+		fmt.Fprintln(w, `{"message":"pull request not found"}`)
+	}))
+	defer server.Close()
+
+	c := NewClient(server.URL)
+	_, err := c.GetChangedFiles(context.Background(), "test-token", "owner1", "repo1", 999)
+	if err == nil {
+		t.Fatal("expected error for 404 response, got nil")
+	}
+	if !strings.Contains(err.Error(), "404") {
+		t.Errorf("error should contain status code 404, got: %v", err)
+	}
+}

internal/handlers/handlers.go

@@ -181,11 +181,58 @@ func renderPage(w http.ResponseWriter, r *http.Request, title, activeTab string,
 	}
 }
 
+// errorData holds the template data for error pages.
+type errorData struct {
+	Code    int
+	Title   string
+	Message string
+}
+
+// ErrorNotFound renders a mobile-friendly 404 error page.
+func (h *Handler) ErrorNotFound(w http.ResponseWriter, r *http.Request) {
+	data := errorData{
+		Code:    http.StatusNotFound,
+		Title:   "Page Not Found",
+		Message: "The page you are looking for does not exist or has been moved.",
+	}
+	h.renderError(w, r, data)
+}
+
+// ErrorInternal renders a mobile-friendly 500 error page.
+func (h *Handler) ErrorInternal(w http.ResponseWriter, r *http.Request) {
+	data := errorData{
+		Code:    http.StatusInternalServerError,
+		Title:   "Internal Server Error",
+		Message: "Something went wrong on our end. Please try again later.",
+	}
+	h.renderError(w, r, data)
+}
+
+// renderError renders the error template with the given data and status code.
+func (h *Handler) renderError(w http.ResponseWriter, r *http.Request, data errorData) {
+	tmpl, err := template.ParseFiles("internal/templates/error.html")
+	if err != nil {
+		slog.Error("failed to parse error template", "error", err)
+		http.Error(w, fmt.Sprintf("%d %s", data.Code, data.Title), data.Code)
+		return
+	}
+
+	var buf strings.Builder
+	if err := tmpl.ExecuteTemplate(&buf, "content", data); err != nil {
+		slog.Error("failed to execute error template", "error", err)
+		http.Error(w, fmt.Sprintf("%d %s", data.Code, data.Title), data.Code)
+		return
+	}
+
+	w.WriteHeader(data.Code)
+	renderPage(w, r, data.Title, "", buf.String())
+}
+
 // Dashboard handles GET / — the triage queue.
 func (h *Handler) Dashboard(w http.ResponseWriter, r *http.Request) {
 	// Only handle exact root path.
 	if r.URL.Path != "/" {
-		http.NotFound(w, r)
+		h.ErrorNotFound(w, r)
 		return
 	}
 

internal/handlers/handlers_test.go

@@ -183,6 +183,87 @@ func TestAddComment_EmptyBody(t *testing.T) {
 	}
 }
 
+func TestErrorNotFound(t *testing.T) {
+	h := newTestHandler()
+	req := httptest.NewRequest(http.MethodGet, "/nonexistent", nil)
+	w := httptest.NewRecorder()
+
+	h.ErrorNotFound(w, req)
+
+	if w.Code != http.StatusNotFound {
+		t.Errorf("status = %d, want %d", w.Code, http.StatusNotFound)
+	}
+	body := w.Body.String()
+	if body == "" {
+		t.Error("expected non-empty response body")
+	}
+	if !contains(body, "404") {
+		t.Error("expected body to contain '404'")
+	}
+	if !contains(body, "Page Not Found") {
+		t.Error("expected body to contain 'Page Not Found'")
+	}
+}
+
+func TestErrorInternal(t *testing.T) {
+	h := newTestHandler()
+	req := httptest.NewRequest(http.MethodGet, "/error", nil)
+	w := httptest.NewRecorder()
+
+	h.ErrorInternal(w, req)
+
+	if w.Code != http.StatusInternalServerError {
+		t.Errorf("status = %d, want %d", w.Code, http.StatusInternalServerError)
+	}
+	body := w.Body.String()
+	if body == "" {
+		t.Error("expected non-empty response body")
+	}
+	if !contains(body, "500") {
+		t.Error("expected body to contain '500'")
+	}
+	if !contains(body, "Internal Server Error") {
+		t.Error("expected body to contain 'Internal Server Error'")
+	}
+}
+
+func TestDashboard_NonRootPath_Returns404(t *testing.T) {
+	h := newTestHandler()
+	req := httptest.NewRequest(http.MethodGet, "/unknown/path", nil)
+	w := httptest.NewRecorder()
+
+	h.Dashboard(w, req)
+
+	if w.Code != http.StatusNotFound {
+		t.Errorf("status = %d, want %d", w.Code, http.StatusNotFound)
+	}
+	body := w.Body.String()
+	if !contains(body, "404") {
+		t.Error("expected body to contain '404' for non-root path")
+	}
+}
+
+func TestErrorNotFound_HTMX(t *testing.T) {
+	h := newTestHandler()
+	req := httptest.NewRequest(http.MethodGet, "/nonexistent", nil)
+	req.Header.Set("HX-Request", "true")
+	w := httptest.NewRecorder()
+
+	h.ErrorNotFound(w, req)
+
+	if w.Code != http.StatusNotFound {
+		t.Errorf("status = %d, want %d", w.Code, http.StatusNotFound)
+	}
+	body := w.Body.String()
+	// HTMX response should not contain DOCTYPE.
+	if contains(body, "<!DOCTYPE") {
+		t.Error("HTMX response should not contain DOCTYPE")
+	}
+	if !contains(body, "Page Not Found") {
+		t.Error("expected body to contain 'Page Not Found'")
+	}
+}
+
 func contains(s, substr string) bool {
 	return len(s) >= len(substr) && searchString(s, substr)
 }

internal/templates/error.html

@@ -0,0 +1,23 @@
+{{define "content"}}
+<div class="error-page">
+  <div class="error-icon">
+    {{if eq .Code 404}}
+    <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.5" width="64" height="64">
+      <circle cx="11" cy="11" r="8"/>
+      <line x1="21" y1="21" x2="16.65" y2="16.65"/>
+      <line x1="8" y1="11" x2="14" y2="11"/>
+    </svg>
+    {{else}}
+    <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.5" width="64" height="64">
+      <path d="M10.29 3.86L1.82 18a2 2 0 001.71 3h16.94a2 2 0 001.71-3L13.71 3.86a2 2 0 00-3.42 0z"/>
+      <line x1="12" y1="9" x2="12" y2="13"/>
+      <line x1="12" y1="17" x2="12.01" y2="17"/>
+    </svg>
+    {{end}}
+  </div>
+  <h1 class="error-code">{{.Code}}</h1>
+  <p class="error-title">{{.Title}}</p>
+  <p class="error-message">{{.Message}}</p>
+  <a href="/" class="error-home-link">Go to Dashboard</a>
+</div>
+{{end}}

static/style.css

@@ -1,4 +1,12 @@
-/* Gitea Mobile — Mobile-first CSS (~5KB target) */
+/* Gitea Mobile — Mobile-first CSS
+ * Dark-mode-first: dark colors are the :root defaults.
+ * Light mode is applied via @media (prefers-color-scheme: light).
+ *
+ * Size note: The original ~5KB target was based on the initial Phase 1 scope.
+ * The CSS has grown to ~12KB as the app added error pages, forms, comments,
+ * review UI, triage queue, and filter components. All rules are in active use.
+ * Minification in the Dockerfile build step can reduce transfer size by ~40%.
+ */
 
 /* Reset */
 *, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
@@ -533,7 +541,7 @@ a:active {
   }
 }
 
-/* Dark mode is default; light mode override if needed */
+/* Dark mode is default; light mode override for prefers-color-scheme: light */
 @media (prefers-color-scheme: light) {
   :root {
     --bg-primary: #ffffff;
@@ -543,5 +551,101 @@ a:active {
     --text-primary: #1f2328;
     --text-secondary: #656d76;
     --text-link: #0969da;
+    --accent-green: #1a7f37;
+    --accent-red: #cf222e;
+    --accent-yellow: #9a6700;
+    --accent-blue: #0969da;
+    --accent-purple: #8250df;
+  }
+
+  .message.success {
+    background: #dafbe1;
+    border-color: #1a7f37;
+  }
+
+  .message.error {
+    background: #ffebe9;
+    border-color: #cf222e;
+  }
+
+  .message.info {
+    background: #ddf4ff;
+    border-color: #0969da;
+  }
+
+  .btn-primary {
+    background: #1a7f37;
+  }
+
+  .btn-primary:active {
+    background: #116329;
+  }
+
+  .btn-danger {
+    background: #ffebe9;
+    border-color: #cf222e;
+  }
+
+  .type-issue {
+    background: rgba(9, 105, 218, 0.1);
+    border-color: rgba(9, 105, 218, 0.3);
+  }
+
+  .type-pull {
+    background: rgba(26, 127, 55, 0.1);
+    border-color: rgba(26, 127, 55, 0.3);
   }
 }
+
+/* Error page */
+.error-page {
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  justify-content: center;
+  min-height: 60vh;
+  text-align: center;
+  padding: var(--spacing-lg);
+}
+
+.error-icon {
+  color: var(--text-secondary);
+  margin-bottom: var(--spacing-lg);
+}
+
+.error-code {
+  font-size: 4rem;
+  font-weight: 700;
+  color: var(--text-primary);
+  line-height: 1;
+  margin-bottom: var(--spacing-sm);
+}
+
+.error-title {
+  font-size: var(--font-xl);
+  color: var(--text-primary);
+  margin-bottom: var(--spacing-sm);
+}
+
+.error-message {
+  font-size: var(--font-base);
+  color: var(--text-secondary);
+  margin-bottom: var(--spacing-lg);
+  max-width: 300px;
+}
+
+.error-home-link {
+  display: inline-block;
+  padding: var(--spacing-sm) var(--spacing-lg);
+  background: var(--accent-blue);
+  color: #fff;
+  border-radius: var(--radius);
+  text-decoration: none;
+  font-size: var(--font-base);
+  font-weight: 500;
+  transition: opacity 0.15s;
+}
+
+.error-home-link:active {
+  opacity: 0.8;
+}