Add configurable PR comment upsert and fix UTF-8 truncation (#411)

## Summary

CI review comments are always created as new comments. This adds an
opt-in `ci.upsert_comments` setting that finds the existing roborev
marker comment and patches it in-place instead.

- Add `ci.upsert_comments` config (global and per-repo, default false)
- Add `FindExistingComment`, `UpsertPRComment`, and `CreatePRComment` in
`internal/github`
- Fall back to creating a new comment when PATCH returns 403/404 (token
mismatch)
- Target the newest marker comment to reduce fallback churn
- Fix UTF-8 truncation: replace `utf8.ValidString` full-string scan with
boundary-only `TrimPartialRune`
- Propagate caller context through `postCIComment` for Ctrl+C
cancellation

### Config

```toml
# Global (~/.roborev/config.toml)
[ci]
upsert_comments = true

# Per-repo (.roborev.toml) — overrides global
[ci]
upsert_comments = false
```

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Wes McKinney <wesmckinn+git@gmail.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: 3 people

cmd/roborev/ci.go

@@ -7,12 +7,12 @@ import (
 	"fmt"
 	"log"
 	"os"
-	"os/exec"
 	"strconv"
 	"strings"
 
 	"github.com/roborev-dev/roborev/internal/config"
 	"github.com/roborev-dev/roborev/internal/git"
+	ghpkg "github.com/roborev-dev/roborev/internal/github"
 	"github.com/roborev-dev/roborev/internal/review"
 	"github.com/spf13/cobra"
 )
@@ -264,8 +264,10 @@ func runCIReview(ctx context.Context, opts ciReviewOpts) error {
 			prNumber = detected
 		}
 
+		upsert := resolveCIUpsertComments(
+			repoCfg, globalCfg)
 		if err := postCIComment(
-			ghRepo, prNumber, comment,
+			ctx, ghRepo, prNumber, comment, upsert,
 		); err != nil {
 			return fmt.Errorf(
 				"post PR comment: %w", err)
@@ -380,6 +382,21 @@ func resolveCISynthesisAgent(
 	return ""
 }
 
+// resolveCIUpsertComments determines whether to upsert PR comments.
+// Priority: repo config > global config > false.
+func resolveCIUpsertComments(
+	repoCfg *config.RepoConfig,
+	globalCfg *config.Config,
+) bool {
+	if repoCfg != nil && repoCfg.CI.UpsertComments != nil {
+		return *repoCfg.CI.UpsertComments
+	}
+	if globalCfg != nil {
+		return globalCfg.CI.UpsertComments
+	}
+	return false
+}
+
 func splitTrimmed(s string) []string {
 	parts := strings.Split(s, ",")
 	out := make([]string, 0, len(parts))
@@ -477,30 +494,18 @@ func extractHeadSHA(gitRef string) string {
 	return gitRef
 }
 
-// postCIComment posts a comment on a GitHub PR using gh CLI.
-// Truncates the body to stay within GitHub's comment limit.
+// postCIComment posts a roborev comment on a GitHub PR.
+// When upsert is true, it finds and patches an existing marker comment;
+// otherwise it always creates a new comment.
 func postCIComment(
+	ctx context.Context,
 	ghRepo string,
 	prNumber int,
 	body string,
+	upsert bool,
 ) error {
-	if len(body) > review.MaxCommentLen {
-		body = body[:review.MaxCommentLen] +
-			"\n\n...(truncated — comment exceeded " +
-			"size limit)"
+	if upsert {
+		return ghpkg.UpsertPRComment(ctx, ghRepo, prNumber, body, nil)
 	}
-
-	ghCmd := exec.Command("gh", "pr", "comment",
-		"--repo", ghRepo,
-		strconv.Itoa(prNumber),
-		"--body-file", "-")
-	ghCmd.Stdin = strings.NewReader(body)
-	ghCmd.Stderr = os.Stderr
-
-	if out, err := ghCmd.Output(); err != nil {
-		return fmt.Errorf(
-			"gh pr comment: %v (output: %s)",
-			err, string(out))
-	}
-	return nil
+	return ghpkg.CreatePRComment(ctx, ghRepo, prNumber, body, nil)
 }

cmd/roborev/ci_test.go

@@ -7,6 +7,8 @@ import (
 	"runtime"
 	"strings"
 	"testing"
+
+	"github.com/roborev-dev/roborev/internal/config"
 )
 
 func TestCIReviewCmd_Help(t *testing.T) {
@@ -235,6 +237,66 @@ func TestResolveReviewTypes_EmptyFlag(t *testing.T) {
 	}
 }
 
+func boolPtr(v bool) *bool { return &v }
+
+func TestResolveCIUpsertComments(t *testing.T) {
+	tests := []struct {
+		name   string
+		repo   *config.RepoConfig
+		global *config.Config
+		want   bool
+	}{
+		{
+			name: "nil/nil defaults to false",
+			repo: nil, global: nil, want: false,
+		},
+		{
+			name:   "global true",
+			repo:   nil,
+			global: &config.Config{CI: config.CIConfig{UpsertComments: true}},
+			want:   true,
+		},
+		{
+			name:   "global false",
+			repo:   nil,
+			global: &config.Config{CI: config.CIConfig{UpsertComments: false}},
+			want:   false,
+		},
+		{
+			name: "repo true overrides global false",
+			repo: &config.RepoConfig{
+				CI: config.RepoCIConfig{UpsertComments: boolPtr(true)},
+			},
+			global: &config.Config{CI: config.CIConfig{UpsertComments: false}},
+			want:   true,
+		},
+		{
+			name: "repo false overrides global true",
+			repo: &config.RepoConfig{
+				CI: config.RepoCIConfig{UpsertComments: boolPtr(false)},
+			},
+			global: &config.Config{CI: config.CIConfig{UpsertComments: true}},
+			want:   false,
+		},
+		{
+			name: "repo nil falls through to global",
+			repo: &config.RepoConfig{
+				CI: config.RepoCIConfig{UpsertComments: nil},
+			},
+			global: &config.Config{CI: config.CIConfig{UpsertComments: true}},
+			want:   true,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := resolveCIUpsertComments(tt.repo, tt.global)
+			if got != tt.want {
+				t.Errorf("resolveCIUpsertComments() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
 func TestSplitTrimmed(t *testing.T) {
 	tests := []struct {
 		in   string

internal/config/config.go

@@ -299,6 +299,11 @@ type CIConfig struct {
 	// Valid values: critical, high, medium, low. Empty means no filter (include all).
 	MinSeverity string `toml:"min_severity"`
 
+	// UpsertComments enables updating existing PR comments instead of
+	// creating new ones. When true, roborev searches for its marker
+	// comment and patches it. Default: false (create a new comment each run).
+	UpsertComments bool `toml:"upsert_comments"`
+
 	// GitHub App authentication (optional — comments appear as bot instead of personal account)
 	GitHubAppConfig
 }
@@ -515,6 +520,10 @@ type RepoCIConfig struct {
 
 	// MinSeverity overrides the minimum severity filter for CI synthesis.
 	MinSeverity string `toml:"min_severity"`
+
+	// UpsertComments overrides the global ci.upsert_comments setting.
+	// Use a pointer so we can distinguish "not set" from "explicitly false".
+	UpsertComments *bool `toml:"upsert_comments"`
 }
 
 // RepoConfig holds per-repo overrides

internal/daemon/ci_poller.go

@@ -20,6 +20,7 @@ import (
 	"github.com/roborev-dev/roborev/internal/agent"
 	"github.com/roborev-dev/roborev/internal/config"
 	gitpkg "github.com/roborev-dev/roborev/internal/git"
+	ghpkg "github.com/roborev-dev/roborev/internal/github"
 	reviewpkg "github.com/roborev-dev/roborev/internal/review"
 	"github.com/roborev-dev/roborev/internal/storage"
 )
@@ -1648,28 +1649,30 @@ func formatPRComment(review *storage.Review, verdict string) string {
 	return b.String()
 }
 
-// postPRComment posts a comment on a GitHub PR using the gh CLI.
-// Truncates the body to stay within GitHub's ~65536 character limit.
+// postPRComment posts a roborev comment on a GitHub PR.
+// When upsert_comments is enabled (per-repo > global > false),
+// it finds and patches an existing marker comment; otherwise it
+// always creates a new comment.
 func (p *CIPoller) postPRComment(ghRepo string, prNumber int, body string) error {
-	if len(body) > reviewpkg.MaxCommentLen {
-		body = body[:reviewpkg.MaxCommentLen] +
-			"\n\n...(truncated — comment exceeded " +
-			"size limit)"
-	}
-
 	ctx, cancel := context.WithTimeout(context.Background(), 60*time.Second)
 	defer cancel()
-	cmd := exec.CommandContext(ctx, "gh", "pr", "comment",
-		"--repo", ghRepo,
-		fmt.Sprintf("%d", prNumber),
-		"--body-file", "-",
-	)
-	cmd.Stdin = strings.NewReader(body)
-	if env := p.ghEnvForRepo(ghRepo); env != nil {
-		cmd.Env = env
+	env := p.ghEnvForRepo(ghRepo)
+	if p.resolveUpsertComments(ghRepo) {
+		return ghpkg.UpsertPRComment(ctx, ghRepo, prNumber, body, env)
 	}
-	if out, err := cmd.CombinedOutput(); err != nil {
-		return fmt.Errorf("gh pr comment: %s: %s", err, string(out))
+	return ghpkg.CreatePRComment(ctx, ghRepo, prNumber, body, env)
+}
+
+// resolveUpsertComments determines whether to upsert PR comments
+// for the given repo. Per-repo config takes priority over global.
+func (p *CIPoller) resolveUpsertComments(ghRepo string) bool {
+	repo, err := p.findLocalRepo(ghRepo)
+	if err == nil && repo != nil {
+		repoCfg, err := loadCIRepoConfig(repo.RootPath)
+		if err == nil && repoCfg != nil &&
+			repoCfg.CI.UpsertComments != nil {
+			return *repoCfg.CI.UpsertComments
+		}
 	}
-	return nil
+	return p.cfgGetter.Config().CI.UpsertComments
 }

internal/daemon/ci_poller_test.go

@@ -3087,3 +3087,54 @@ func TestCIPollerProcessPR_AgentFailureSetsErrorStatus(t *testing.T) {
 		)
 	}
 }
+
+func TestResolveUpsertComments_DefaultFalse(t *testing.T) {
+	h := newCIPollerHarness(t, "https://github.com/acme/api.git")
+	if h.Poller.resolveUpsertComments("acme/api") {
+		t.Fatal("expected false by default")
+	}
+}
+
+func TestResolveUpsertComments_GlobalTrue(t *testing.T) {
+	h := newCIPollerHarness(t, "https://github.com/acme/api.git")
+	h.Cfg.CI.UpsertComments = true
+	if !h.Poller.resolveUpsertComments("acme/api") {
+		t.Fatal("expected true from global config")
+	}
+}
+
+func TestResolveUpsertComments_RepoOverridesGlobal(t *testing.T) {
+	h := newCIPollerHarness(t, "https://github.com/acme/api.git")
+	h.Cfg.CI.UpsertComments = true
+
+	// Write a .roborev.toml in the repo that disables upsert.
+	tomlPath := filepath.Join(h.RepoPath, ".roborev.toml")
+	err := os.WriteFile(tomlPath, []byte(
+		"[ci]\nupsert_comments = false\n",
+	), 0o644)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if h.Poller.resolveUpsertComments("acme/api") {
+		t.Fatal("expected repo config (false) to override global (true)")
+	}
+}
+
+func TestResolveUpsertComments_RepoEnablesOverGlobal(t *testing.T) {
+	h := newCIPollerHarness(t, "https://github.com/acme/api.git")
+	// Global default is false.
+
+	// Write a .roborev.toml in the repo that enables upsert.
+	tomlPath := filepath.Join(h.RepoPath, ".roborev.toml")
+	err := os.WriteFile(tomlPath, []byte(
+		"[ci]\nupsert_comments = true\n",
+	), 0o644)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if !h.Poller.resolveUpsertComments("acme/api") {
+		t.Fatal("expected repo config (true) to override global (false)")
+	}
+}