Refine the merge TUI and simplify the async-merge client

Follow-up polish for `gh stack merge` (the command itself landed in the
previous commit). These changes refine the interactive wizard, enrich the
PR picker, and replace the merge client's bespoke HTTP handling with the
standard go-gh REST client.

Wizard and stepper:
- Redesign the top stepper as a segmented bar: completed steps are green,
  the active step is the brightest, and upcoming steps are dimmed. Steps
  are separated by a Powerline arrow that blends into the shading, with a
  graceful fallback to abutting segments on terminals that lack the glyph
  (e.g. Apple Terminal). Set GH_STACK_POWERLINE=1/0 to override detection.
- Show the stack number in the header ("Merge stack #123").
- Hide the header and stepper once the merge is submitted so the live
  progress view stands on its own.

PR picker:
- Render each pull request on two lines: the title (white/black, a touch
  bolder when selected) above its "#number • branch" (gray, fainter when
  deselected). Titles are fetched in one batched GraphQL query (PRTitles)
  and fall back to the branch name.
- Scroll long stacks in a fixed 10-item window with persistent "N more"
  indicators, so the list no longer jumps as those hints appear and
  disappear. Add shift+up / shift+down to jump to the top or bottom.

Progress and outcome:
- Always render a status line ("Submitting merge request...") so it does
  not pop in later and shift the view, and normalize messages to end in an
  ellipsis.
- Print the final result from the command layer rather than the TUI: a
  success line that includes the merge commit SHA
  ("Merged #1, #2 into main (abc1234)"), an atomic-rollback note on
  failure, a distinct message when the user stops watching an in-flight
  merge, and "Cancelled operation, nothing merged" on cancel.
- Clamp every rendered line to the terminal width so resizing no longer
  leaves duplicated header lines behind, and make truncation ANSI-aware.

Async-merge client:
- Use the go-gh REST client (c.rest.Put / c.rest.Get) for both the submit
  and poll endpoints, removing the bespoke http.Client, base-URL helper,
  and manual response decoding. The REST client discards non-2xx bodies,
  but that only costs the rare 400 message and 409 UUID: real merge
  failures still surface through the 200 poll body, and the in-range PRs
  are validated open, non-draft, and non-merged before submitting.
- Add classifyAsyncMergeError to map status codes to clear errors (404
  unavailable, 409 already exists, 400 no longer mergeable) and drop the
  now-unused AsyncMergeResult.StatusCode field. Rework the client tests to
  drive the REST client through a stub http.RoundTripper.

Author: skarim

cmd/merge.go

@@ -141,7 +141,7 @@ func runMerge(cfg *config.Config, opts *mergeOptions, args []string) error {
 	base := remoteStack.Base.Ref
 
 	if cfg.IsInteractive() && !opts.yes {
-		return runMergeInteractive(cfg, client, base, candidates, allowed, mergeCfg.DefaultMethod, method, preselectIndex, opts)
+		return runMergeInteractive(cfg, client, remoteStack.Number, base, candidates, allowed, mergeCfg.DefaultMethod, method, preselectIndex, opts)
 	}
 
 	// Non-interactive (or --yes): merge the whole stack (or up to the given PR)
@@ -260,16 +260,30 @@ func resolveActiveRemoteStack(cfg *config.Config, client github.ClientOps) (*git
 	return rs, nil
 }
 
-func runMergeInteractive(cfg *config.Config, client github.ClientOps, base string, candidates []mergeview.PRItem, allowed []string, viewerDefault, methodFlag string, preselectIndex int, opts *mergeOptions) error {
+func runMergeInteractive(cfg *config.Config, client github.ClientOps, stackNumber int, base string, candidates []mergeview.PRItem, allowed []string, viewerDefault, methodFlag string, preselectIndex int, opts *mergeOptions) error {
 	defaultMethod := viewerDefault
 	if methodFlag != "" {
 		defaultMethod = methodFlag
 	}
 
+	// Enrich the picker with PR titles (best-effort; the branch is shown either way).
+	nums := make([]int, len(candidates))
+	for i, c := range candidates {
+		nums[i] = c.Number
+	}
+	if titles, err := client.PRTitles(nums); err == nil {
+		for i := range candidates {
+			if t := titles[candidates[i].Number]; t != "" {
+				candidates[i].Title = t
+			}
+		}
+	}
+
 	submit, poll := mergeFuncs(client)
 
 	model := mergeview.New(mergeview.Options{
 		PRs:               candidates,
+		StackNumber:       stackNumber,
 		BaseRef:           base,
 		AllowedMethods:    allowed,
 		DefaultMethod:     defaultMethod,
@@ -292,13 +306,21 @@ func runMergeInteractive(cfg *config.Config, client github.ClientOps, base strin
 			warnAsyncMergeUnavailable(cfg)
 			return ErrStacksUnavailable
 		}
+		cfg.Errorf("merge failed: %s", out.Err)
 		return ErrAPIFailure
 	case out.Merged:
+		mergedSuccess(cfg, prNumberList(out.MergedPRs), base, out.SHA)
 		return nil
 	case out.Failed:
+		cfg.Errorf("merge failed: %s", out.Message)
+		cfg.Printf("The stack is atomic, so nothing was merged.")
 		return mergeFailureExit(out.Message)
+	case out.WatchStopped:
+		cfg.Infof("Stopped watching. Merge is still in progress. Check the pull requests on GitHub.")
+		return ErrSilent
 	default:
-		// Cancelled, or watching was stopped while the merge continued.
+		// Cancelled via esc/ctrl+c before submitting.
+		cfg.Infof("Cancelled operation, nothing merged")
 		return ErrSilent
 	}
 }
@@ -320,18 +342,15 @@ func runMergeHeadless(cfg *config.Config, client github.ClientOps, base string,
 	}
 
 	if res.Merged {
-		cfg.Successf("Merged %s into %s", list, base)
+		mergedSuccess(cfg, list, base, res.Details.SHA)
 		return nil
 	}
-	if !res.Queued {
-		cfg.Errorf("cannot merge: %s", res.Details.Message)
-		return ErrAPIFailure
-	}
-	if res.StatusCode == http.StatusConflict {
-		cfg.Infof("A merge request already exists for this stack; tracking it.")
-	}
 
 	uuid := res.Details.UUID
+	if uuid == "" {
+		cfg.Errorf("merge did not start as expected")
+		return ErrAPIFailure
+	}
 	interval := opts.pollInterval
 	if interval <= 0 {
 		interval = time.Second
@@ -350,10 +369,7 @@ func runMergeHeadless(cfg *config.Config, client github.ClientOps, base string,
 			return ErrAPIFailure
 		}
 		if status.Merged {
-			cfg.Successf("Merged %s into %s", list, base)
-			if sha := status.Details.SHA; sha != "" {
-				cfg.Printf("  Merge commit %s", shortMergeSHA(sha))
-			}
+			mergedSuccess(cfg, list, base, status.Details.SHA)
 			return nil
 		}
 		if !status.Queued {
@@ -414,7 +430,7 @@ func mergeCandidates(rs *github.RemoteStack) (items []mergeview.PRItem, blocker
 			b := pr
 			return items, &b
 		}
-		items = append(items, mergeview.PRItem{Number: pr.Number, Title: pr.Head.Ref})
+		items = append(items, mergeview.PRItem{Number: pr.Number, Branch: pr.Head.Ref})
 	}
 	return items, nil
 }
@@ -572,6 +588,16 @@ func shortMergeSHA(sha string) string {
 	return sha
 }
 
+// mergedSuccess prints the merge success line, appending the merge commit SHA in
+// parentheses when known: "Merged #1, #2 into main (abc1234)".
+func mergedSuccess(cfg *config.Config, list, base, sha string) {
+	if sha != "" {
+		cfg.Successf("Merged %s into %s (%s)", list, base, shortMergeSHA(sha))
+		return
+	}
+	cfg.Successf("Merged %s into %s", list, base)
+}
+
 func isNotFound(err error) bool {
 	var httpErr *api.HTTPError
 	return errors.As(err, &httpErr) && httpErr.StatusCode == http.StatusNotFound

cmd/merge_test.go

@@ -1,6 +1,7 @@
 package cmd
 
 import (
+	"errors"
 	"net/http"
 	"testing"
 	"time"
@@ -92,10 +93,10 @@ func TestRunMerge_NoArg_MergesWholeStack(t *testing.T) {
 		},
 		MergeStackAsyncFn: func(pr int, method string) (*github.AsyncMergeResult, error) {
 			gotPR, gotMethod = pr, method
-			return &github.AsyncMergeResult{Queued: true, Details: github.AsyncMergeDetails{UUID: "u"}, StatusCode: 202}, nil
+			return &github.AsyncMergeResult{Queued: true, Details: github.AsyncMergeDetails{UUID: "u"}}, nil
 		},
 		GetAsyncMergeResultFn: func(pr int, uuid string) (*github.AsyncMergeResult, error) {
-			return &github.AsyncMergeResult{Merged: true, Details: github.AsyncMergeDetails{SHA: "abc1234"}, StatusCode: 200}, nil
+			return &github.AsyncMergeResult{Merged: true, Details: github.AsyncMergeDetails{SHA: "abc1234"}}, nil
 		},
 	}
 
@@ -294,15 +295,16 @@ func TestRunMerge_SubmitNotMergeable(t *testing.T) {
 			return remoteStack(7, "main", openStackPR(1, "b1"), openStackPR(2, "b2")), nil
 		},
 		MergeStackAsyncFn: func(pr int, method string) (*github.AsyncMergeResult, error) {
-			return &github.AsyncMergeResult{Queued: false, Merged: false, Details: github.AsyncMergeDetails{Message: "Pull request is closed."}, StatusCode: 400}, nil
+			return nil, errors.New("the stack can no longer be merged as requested; refresh and try again")
 		},
 	}
 
 	err := runMerge(cfg, fastOptions(), []string{"7"})
 	output := collectOutput(cfg, outR, errR)
 
 	assert.ErrorIs(t, err, ErrAPIFailure)
-	assert.Contains(t, output, "cannot merge: Pull request is closed.")
+	assert.Contains(t, output, "failed to start merge")
+	assert.Contains(t, output, "can no longer be merged")
 }
 
 func TestRunMerge_PollFailedConflict(t *testing.T) {
@@ -312,7 +314,7 @@ func TestRunMerge_PollFailedConflict(t *testing.T) {
 			return remoteStack(7, "main", openStackPR(1, "b1"), openStackPR(2, "b2")), nil
 		},
 		MergeStackAsyncFn: func(pr int, method string) (*github.AsyncMergeResult, error) {
-			return &github.AsyncMergeResult{Queued: true, Details: github.AsyncMergeDetails{UUID: "u"}, StatusCode: 202}, nil
+			return &github.AsyncMergeResult{Queued: true, Details: github.AsyncMergeDetails{UUID: "u"}}, nil
 		},
 		GetAsyncMergeResultFn: func(pr int, uuid string) (*github.AsyncMergeResult, error) {
 			return &github.AsyncMergeResult{Queued: false, Merged: false, Details: github.AsyncMergeDetails{Message: "Merge conflict: could not merge."}}, nil
@@ -334,7 +336,7 @@ func TestRunMerge_AlreadyMergedOnSubmit(t *testing.T) {
 			return remoteStack(7, "main", openStackPR(1, "b1"), openStackPR(2, "b2")), nil
 		},
 		MergeStackAsyncFn: func(pr int, method string) (*github.AsyncMergeResult, error) {
-			return &github.AsyncMergeResult{Merged: true, Details: github.AsyncMergeDetails{SHA: "abc"}, StatusCode: 200}, nil
+			return &github.AsyncMergeResult{Merged: true, Details: github.AsyncMergeDetails{SHA: "abc"}}, nil
 		},
 	}
 
@@ -453,13 +455,13 @@ func TestMergeCandidates(t *testing.T) {
 	t.Run("leading merged skipped", func(t *testing.T) {
 		items, blocker := mergeCandidates(remoteStack(1, "main", mergedStackPR(1, "a"), openStackPR(2, "b"), openStackPR(3, "c")))
 		assert.Nil(t, blocker)
-		assert.Equal(t, []mergeview.PRItem{{Number: 2, Title: "b"}, {Number: 3, Title: "c"}}, items)
+		assert.Equal(t, []mergeview.PRItem{{Number: 2, Branch: "b"}, {Number: 3, Branch: "c"}}, items)
 	})
 	t.Run("draft blocks above", func(t *testing.T) {
 		items, blocker := mergeCandidates(remoteStack(1, "main", openStackPR(1, "a"), draftStackPR(2, "b"), openStackPR(3, "c")))
 		require.NotNil(t, blocker)
 		assert.Equal(t, 2, blocker.Number)
-		assert.Equal(t, []mergeview.PRItem{{Number: 1, Title: "a"}}, items)
+		assert.Equal(t, []mergeview.PRItem{{Number: 1, Branch: "a"}}, items)
 	})
 	t.Run("closed blocks", func(t *testing.T) {
 		items, blocker := mergeCandidates(remoteStack(1, "main", closedStackPR(1, "a"), openStackPR(2, "b")))

internal/github/client_interface.go

@@ -20,6 +20,7 @@ type ClientOps interface {
 	RepoMergeConfig() (*RepoMergeConfig, error)
 	MergeStackAsync(prNumber int, method string) (*AsyncMergeResult, error)
 	GetAsyncMergeResult(prNumber int, uuid string) (*AsyncMergeResult, error)
+	PRTitles(numbers []int) (map[int]string, error)
 }
 
 // Compile-time check that Client satisfies ClientOps.