diff --git a/README.md b/README.md
index fdf6b7b..e827337 100644
--- a/README.md
+++ b/README.md
@@ -1,6 +1,6 @@
 # gh-threads
 
-A read-only terminal UI for people receiving GitHub pull-request reviews. It
+A terminal UI for people receiving GitHub pull-request reviews. It
 shows open PRs and a scrollable PR dashboard with the description, branches,
 review state, checks, people, labels, milestone, activity, change statistics,
 thread totals, submitted reviews, and the PR conversation. Review threads and
@@ -140,6 +140,8 @@ history and metadata.
 | `/` | Fuzzy-search paths and filter with `status:`, `author:`, `updated:true` |
 | `F` | Clear active thread filters |
 | `n` / `N` | Next / previous thread with a new update |
+| `c` | Compose a reply to the selected thread |
+| `R` | Resolve or unresolve the selected thread |
 | `↑` / `↓` | Choose a fuzzy-search match |
 | `g` / `G` | First / last item |
 | `enter` / `l` | Open the selected PR dashboard or its review threads |
@@ -151,13 +153,20 @@ history and metadata.
 | `r` | Refresh now |
 | `q` | Quit |
 
+The reply composer appears inline beneath the selected thread so its code and
+comments remain visible while writing. It supports multiple lines: `enter`
+inserts a newline, `ctrl-s` opens the rendered confirmation preview, and `esc`
+cancels. Replies and resolution changes require an explicit `y` confirmation.
+Write keys remain disabled for cached snapshots, during refreshes, and whenever
+GitHub does not grant the corresponding per-thread capability.
+
 ## Current scope
 
-The application is intentionally read-only. The dashboard and contextual help
-show the write capability gate, including why each future write action is
-unavailable. Read state persists beside the configuration, and recent PR data
-is cached for offline fallback. Check contexts and annotations are paginated.
-GitHub features which depend
+The application can reply to review threads and resolve or unresolve them.
+Other write operations remain disabled. The dashboard shows the capability
+gate, including why each action is unavailable. Read state
+persists beside the configuration, and recent PR data is cached for offline
+fallback. Check contexts and annotations are paginated. GitHub features which depend
 on server-side context, such as unfurling issue references or displaying
 uploaded images, are represented textually in the terminal. See
 [`TODO.md`](TODO.md) for remaining read-only work and write-support preparation.
diff --git a/TODO.md b/TODO.md
index 54f362c..e0b0eb6 100644
--- a/TODO.md
+++ b/TODO.md
@@ -31,8 +31,9 @@ The following read-only improvements remain before or alongside write support.
 
 ## Preparation for write support
 
-- Fetch per-comment update/delete permissions and the exact reply target IDs.
+- Fetch per-comment update/delete permissions.
 - Define head-SHA conflict handling for comments and suggestions composed
   against an older revision.
-- Design confirmation and optimistic-update behavior for resolving threads,
-  submitting reviews, and applying suggestions.
+- Design confirmation and optimistic-update behavior for submitting reviews
+  and applying suggestions. Thread replies and resolution changes now use
+  confirmed server responses.
diff --git a/cache.go b/cache.go
index 7dd7a14..1e0c266 100644
--- a/cache.go
+++ b/cache.go
@@ -118,6 +118,26 @@ func (c *CachedGitHubService) LivePullRequest(
 	return details, nil
 }
 
+func (c *CachedGitHubService) SetThreadResolved(
+	ctx context.Context, threadID string, resolved bool,
+) (ReviewThread, error) {
+	writer, ok := c.remote.(GitHubWriteService)
+	if !ok {
+		return ReviewThread{}, errors.New("GitHub service does not support write actions")
+	}
+	return writer.SetThreadResolved(ctx, threadID, resolved)
+}
+
+func (c *CachedGitHubService) ReplyToThread(
+	ctx context.Context, threadID, body string,
+) (ReviewComment, error) {
+	writer, ok := c.remote.(GitHubWriteService)
+	if !ok {
+		return ReviewComment{}, errors.New("GitHub service does not support write actions")
+	}
+	return writer.ReplyToThread(ctx, threadID, body)
+}
+
 func (c *CachedGitHubService) pullRequestsKey(owner, repo string, limit int, showAll bool) string {
 	return fmt.Sprintf("prs:%s/%s:%d:%t", owner, repo, limit, showAll)
 }
diff --git a/github.go b/github.go
index 08cddf5..a1dd75d 100644
--- a/github.go
+++ b/github.go
@@ -20,6 +20,11 @@ type GitHubService interface {
 	GetPullRequest(context.Context, string, string, int) (PRDetails, error)
 }
 
+type GitHubWriteService interface {
+	SetThreadResolved(context.Context, string, bool) (ReviewThread, error)
+	ReplyToThread(context.Context, string, string) (ReviewComment, error)
+}
+
 type GitHubClient struct {
 	endpoint string
 	token    string
@@ -422,6 +427,38 @@ query CheckAnnotationsPage($id: ID!, $after: String) {
   }
 }`
 
+const resolveThreadMutation = `
+mutation ResolveReviewThread($input: ResolveReviewThreadInput!) {
+  resolveReviewThread(input: $input) {
+    thread {
+      id isResolved isOutdated viewerCanResolve viewerCanUnresolve viewerCanReply path
+      line originalLine diffSide startLine originalStartLine startDiffSide
+    }
+  }
+}`
+
+const unresolveThreadMutation = `
+mutation UnresolveReviewThread($input: UnresolveReviewThreadInput!) {
+  unresolveReviewThread(input: $input) {
+    thread {
+      id isResolved isOutdated viewerCanResolve viewerCanUnresolve viewerCanReply path
+      line originalLine diffSide startLine originalStartLine startDiffSide
+    }
+  }
+}`
+
+const replyToThreadMutation = `
+mutation ReplyToReviewThread($input: AddPullRequestReviewThreadReplyInput!) {
+  addPullRequestReviewThreadReply(input: $input) {
+    comment {
+      id body diffHunk createdAt url outdated
+      line startLine originalLine originalStartLine
+      originalCommit { oid }
+      author { login }
+    }
+  }
+}`
+
 type githubActor struct {
 	Login string `json:"login"`
 	Name  string `json:"name"`
@@ -1047,6 +1084,63 @@ func (c *GitHubClient) GetPullRequest(ctx context.Context, owner, name string, n
 	return details, nil
 }
 
+func (c *GitHubClient) SetThreadResolved(
+	ctx context.Context, threadID string, resolved bool,
+) (ReviewThread, error) {
+	query := resolveThreadMutation
+	variables := map[string]any{"input": map[string]any{"threadId": threadID}}
+	if resolved {
+		var data struct {
+			ResolveReviewThread *struct {
+				Thread *githubReviewThread
+			}
+		}
+		if err := c.query(ctx, query, variables, &data); err != nil {
+			return ReviewThread{}, err
+		}
+		if data.ResolveReviewThread == nil || data.ResolveReviewThread.Thread == nil {
+			return ReviewThread{}, errors.New("GitHub returned no resolved review thread")
+		}
+		return convertReviewThread(*data.ResolveReviewThread.Thread), nil
+	}
+
+	var data struct {
+		UnresolveReviewThread *struct {
+			Thread *githubReviewThread
+		}
+	}
+	if err := c.query(ctx, unresolveThreadMutation, variables, &data); err != nil {
+		return ReviewThread{}, err
+	}
+	if data.UnresolveReviewThread == nil || data.UnresolveReviewThread.Thread == nil {
+		return ReviewThread{}, errors.New("GitHub returned no unresolved review thread")
+	}
+	return convertReviewThread(*data.UnresolveReviewThread.Thread), nil
+}
+
+func (c *GitHubClient) ReplyToThread(
+	ctx context.Context, threadID, body string,
+) (ReviewComment, error) {
+	var data struct {
+		AddPullRequestReviewThreadReply *struct {
+			Comment *githubReviewComment
+		}
+	}
+	if err := c.query(ctx, replyToThreadMutation, map[string]any{
+		"input": map[string]any{
+			"pullRequestReviewThreadId": threadID,
+			"body":                      body,
+		},
+	}, &data); err != nil {
+		return ReviewComment{}, err
+	}
+	if data.AddPullRequestReviewThreadReply == nil ||
+		data.AddPullRequestReviewThreadReply.Comment == nil {
+		return ReviewComment{}, errors.New("GitHub returned no review reply")
+	}
+	return convertReviewComment(*data.AddPullRequestReviewThreadReply.Comment), nil
+}
+
 func convertReviewThread(thread githubReviewThread) ReviewThread {
 	item := ReviewThread{
 		ID: thread.ID, Path: thread.Path, DiffSide: thread.DiffSide,
@@ -1068,17 +1162,21 @@ func convertReviewThread(thread githubReviewThread) ReviewThread {
 		item.DiffSide = thread.StartDiffSide
 	}
 	for _, comment := range thread.Comments.Nodes {
-		item.Comments = append(item.Comments, ReviewComment{
-			ID: comment.ID, Author: actorLogin(comment.Author), Body: comment.Body,
-			DiffHunk: comment.DiffHunk, CreatedAt: comment.CreatedAt, URL: comment.URL,
-			Line: intValue(comment.Line), StartLine: intValue(comment.StartLine),
-			OriginalLine: intValue(comment.OriginalLine), OriginalStartLine: intValue(comment.OriginalStartLine),
-			OriginalCommitOID: commitOID(comment.OriginalCommit), Outdated: comment.Outdated,
-		})
+		item.Comments = append(item.Comments, convertReviewComment(comment))
 	}
 	return item
 }
 
+func convertReviewComment(comment githubReviewComment) ReviewComment {
+	return ReviewComment{
+		ID: comment.ID, Author: actorLogin(comment.Author), Body: comment.Body,
+		DiffHunk: comment.DiffHunk, CreatedAt: comment.CreatedAt, URL: comment.URL,
+		Line: intValue(comment.Line), StartLine: intValue(comment.StartLine),
+		OriginalLine: intValue(comment.OriginalLine), OriginalStartLine: intValue(comment.OriginalStartLine),
+		OriginalCommitOID: commitOID(comment.OriginalCommit), Outdated: comment.Outdated,
+	}
+}
+
 func actorLogin(actor *githubActor) string {
 	if actor == nil || actor.Login == "" {
 		return "[ghost]"
diff --git a/github_test.go b/github_test.go
index d5b3856..15f1d9f 100644
--- a/github_test.go
+++ b/github_test.go
@@ -119,6 +119,62 @@ func TestGraphQLErrorsAreReturned(t *testing.T) {
 	}
 }
 
+func TestThreadWriteMutationsUseThreadIDs(t *testing.T) {
+	requests := 0
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		requests++
+		var request graphQLRequest
+		if err := json.NewDecoder(r.Body).Decode(&request); err != nil {
+			t.Fatal(err)
+		}
+		input, _ := request.Variables["input"].(map[string]any)
+		switch {
+		case strings.Contains(request.Query, "unresolveReviewThread"):
+			if input["threadId"] != "thread" {
+				t.Fatalf("unresolve input = %#v", input)
+			}
+			_, _ = w.Write([]byte(`{"data":{"unresolveReviewThread":{"thread":{
+				"id":"thread","path":"a.go","isResolved":false,"viewerCanResolve":true
+			}}}}`))
+		case strings.Contains(request.Query, "resolveReviewThread"):
+			if input["threadId"] != "thread" {
+				t.Fatalf("resolve input = %#v", input)
+			}
+			_, _ = w.Write([]byte(`{"data":{"resolveReviewThread":{"thread":{
+				"id":"thread","path":"a.go","isResolved":true,"viewerCanUnresolve":true
+			}}}}`))
+		case strings.Contains(request.Query, "addPullRequestReviewThreadReply"):
+			if input["pullRequestReviewThreadId"] != "thread" || input["body"] != "reply body" {
+				t.Fatalf("reply input = %#v", input)
+			}
+			_, _ = w.Write([]byte(`{"data":{"addPullRequestReviewThreadReply":{"comment":{
+				"id":"comment","body":"reply body","createdAt":"2026-01-01T00:00:00Z",
+				"url":"https://example/comment","author":{"login":"me"}
+			}}}}`))
+		default:
+			t.Fatalf("unexpected mutation: %s", request.Query)
+		}
+	}))
+	defer server.Close()
+
+	client := NewGitHubClient(server.URL, "secret")
+	resolved, err := client.SetThreadResolved(context.Background(), "thread", true)
+	if err != nil || !resolved.IsResolved || !resolved.ViewerCanUnresolve {
+		t.Fatalf("resolve result = %#v, error = %v", resolved, err)
+	}
+	unresolved, err := client.SetThreadResolved(context.Background(), "thread", false)
+	if err != nil || unresolved.IsResolved || !unresolved.ViewerCanResolve {
+		t.Fatalf("unresolve result = %#v, error = %v", unresolved, err)
+	}
+	comment, err := client.ReplyToThread(context.Background(), "thread", "reply body")
+	if err != nil || comment.ID != "comment" || comment.Author != "me" || comment.Body != "reply body" {
+		t.Fatalf("reply result = %#v, error = %v", comment, err)
+	}
+	if requests != 3 {
+		t.Fatalf("mutation requests = %d, want 3", requests)
+	}
+}
+
 func TestCheckContextsAndAnnotationsArePaginated(t *testing.T) {
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		var request graphQLRequest
diff --git a/main.go b/main.go
index 5c2d7a1..e544bbe 100644
--- a/main.go
+++ b/main.go
@@ -157,3 +157,5 @@ func exitf(format string, args ...any) {
 
 // Keep interface drift visible at compile time.
 var _ GitHubService = (*GitHubClient)(nil)
+var _ GitHubWriteService = (*GitHubClient)(nil)
+var _ GitHubWriteService = (*CachedGitHubService)(nil)
diff --git a/tui.go b/tui.go
index 5d251ba..be79f4a 100644
--- a/tui.go
+++ b/tui.go
@@ -2,6 +2,7 @@ package main
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"hash/fnv"
 	"slices"
@@ -31,6 +32,30 @@ const (
 
 type tickMsg time.Time
 type pathTickMsg time.Time
+
+type writeMode int
+
+const (
+	writeNone writeMode = iota
+	writeReply
+	writeReplyConfirm
+	writeReplyBusy
+	writeResolveConfirm
+	writeResolveBusy
+)
+
+type threadResolvedMsg struct {
+	threadID string
+	thread   ReviewThread
+	err      error
+}
+
+type threadRepliedMsg struct {
+	threadID string
+	comment  ReviewComment
+	err      error
+}
+
 type prsLoadedMsg struct {
 	prs    []PullRequest
 	err    error
@@ -71,6 +96,10 @@ type App struct {
 	searchOrigin  int
 	helpVisible   bool
 	helpScroll    int
+	writeMode     writeMode
+	writeThreadID string
+	replyDraft    string
+	resolveTarget bool
 
 	foldResolved           bool
 	threadListWidthPercent int
@@ -220,6 +249,134 @@ func (m App) loadLiveDetails(pr PullRequest) tea.Cmd {
 	}
 }
 
+func (m *App) startReply() {
+	thread := m.selectedThread()
+	if reason := m.writeActionUnavailable("reply", thread); reason != "" {
+		m.err = errors.New(reason)
+		return
+	}
+	m.writeMode, m.writeThreadID, m.replyDraft, m.err = writeReply, thread.ID, "", nil
+	m.folded[thread.ID] = false
+	m.focus = threadDetailPane
+	m.scroll = m.detailMaxScroll()
+}
+
+func (m *App) startResolveToggle() {
+	thread := m.selectedThread()
+	if reason := m.writeActionUnavailable("resolve", thread); reason != "" {
+		m.err = errors.New(reason)
+		return
+	}
+	m.writeMode, m.writeThreadID, m.resolveTarget, m.err =
+		writeResolveConfirm, thread.ID, !thread.IsResolved, nil
+}
+
+func (m App) writeActionUnavailable(action string, thread *ReviewThread) string {
+	if m.loading {
+		return "write action unavailable while PR data is refreshing"
+	}
+	if m.details.FromCache {
+		return "write action unavailable from an offline cached snapshot"
+	}
+	if _, ok := m.service.(GitHubWriteService); !ok {
+		return "configured GitHub service does not support write actions"
+	}
+	if thread == nil {
+		return "select a review thread first"
+	}
+	switch action {
+	case "reply":
+		if !thread.ViewerCanReply {
+			return "GitHub did not grant reply permission for this thread"
+		}
+	case "resolve":
+		if thread.IsResolved && !thread.ViewerCanUnresolve {
+			return "GitHub did not grant unresolve permission for this thread"
+		}
+		if !thread.IsResolved && !thread.ViewerCanResolve {
+			return "GitHub did not grant resolve permission for this thread"
+		}
+	}
+	return ""
+}
+
+func (m App) updateWriteInput(key tea.KeyMsg) (tea.Model, tea.Cmd) {
+	k := key.String()
+	if k == "ctrl+c" {
+		return m, tea.Quit
+	}
+	switch m.writeMode {
+	case writeReply:
+		switch k {
+		case "esc":
+			m.writeMode, m.replyDraft, m.writeThreadID = writeNone, "", ""
+			m.scroll = min(m.scroll, m.detailMaxScroll())
+		case "ctrl+s":
+			if strings.TrimSpace(m.replyDraft) == "" {
+				m.err = errors.New("reply cannot be empty")
+			} else {
+				m.writeMode, m.err = writeReplyConfirm, nil
+			}
+		case "enter":
+			m.replyDraft += "\n"
+		case "backspace":
+			runes := []rune(m.replyDraft)
+			if len(runes) > 0 {
+				m.replyDraft = string(runes[:len(runes)-1])
+			}
+			m.err = nil
+		default:
+			if key.Type == tea.KeyRunes || key.Type == tea.KeySpace {
+				m.replyDraft += string(key.Runes)
+				m.err = nil
+			}
+		}
+		if m.writeMode == writeReply {
+			m.scroll = m.detailMaxScroll()
+		}
+	case writeReplyConfirm:
+		switch k {
+		case "y":
+			m.writeMode = writeReplyBusy
+			return m, m.submitReply()
+		case "n", "esc":
+			m.writeMode = writeReply
+			m.scroll = m.detailMaxScroll()
+		}
+	case writeResolveConfirm:
+		switch k {
+		case "y":
+			m.writeMode = writeResolveBusy
+			return m, m.submitResolution()
+		case "n", "esc":
+			m.writeMode, m.writeThreadID = writeNone, ""
+		}
+	}
+	return m, nil
+}
+
+func (m App) submitReply() tea.Cmd {
+	writer := m.service.(GitHubWriteService)
+	threadID, body := m.writeThreadID, strings.TrimRight(m.replyDraft, "\n")
+	return func() tea.Msg {
+		ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
+		defer cancel()
+		comment, err := writer.ReplyToThread(ctx, threadID, body)
+		return threadRepliedMsg{threadID: threadID, comment: comment, err: err}
+	}
+}
+
+func (m App) submitResolution() tea.Cmd {
+	writer := m.service.(GitHubWriteService)
+	threadID, resolved := m.writeThreadID, m.resolveTarget
+	return func() tea.Msg {
+		ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
+		defer cancel()
+		thread, err := writer.SetThreadResolved(ctx, threadID, resolved)
+		return threadResolvedMsg{threadID: threadID, thread: thread, err: err}
+	}
+}
+
 func (m App) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 	switch msg := msg.(type) {
 	case tea.WindowSizeMsg:
@@ -328,6 +485,53 @@ func (m App) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 		} else {
 			m.lastRefresh = time.Now()
 		}
+	case threadResolvedMsg:
+		m.writeMode = writeNone
+		if msg.err != nil {
+			m.err = fmt.Errorf("change thread resolution: %w", msg.err)
+			return m, nil
+		}
+		selected := ""
+		if m.threadIndex >= 0 && m.threadIndex < len(m.details.Threads) {
+			selected = m.details.Threads[m.threadIndex].ID
+		}
+		for index := range m.details.Threads {
+			if m.details.Threads[index].ID != msg.threadID {
+				continue
+			}
+			thread := &m.details.Threads[index]
+			thread.IsResolved = msg.thread.IsResolved
+			thread.IsOutdated = msg.thread.IsOutdated
+			thread.ViewerCanResolve = msg.thread.ViewerCanResolve
+			thread.ViewerCanUnresolve = msg.thread.ViewerCanUnresolve
+			thread.ViewerCanReply = msg.thread.ViewerCanReply
+			m.folded[thread.ID] = thread.IsResolved && m.foldResolved
+			break
+		}
+		sortReviewThreads(m.details.Threads, m.threadStatusOrder, m.threadWithinStatus)
+		m.threadIndex = indexThread(m.details.Threads, selected)
+		m.writeThreadID = ""
+		m.err = nil
+		m.lastRefresh = time.Now()
+	case threadRepliedMsg:
+		if msg.err != nil {
+			m.writeMode = writeReply
+			m.err = fmt.Errorf("reply to review thread: %w", msg.err)
+			m.scroll = m.detailMaxScroll()
+			return m, nil
+		}
+		m.writeMode = writeNone
+		for index := range m.details.Threads {
+			if m.details.Threads[index].ID == msg.threadID {
+				m.details.Threads[index].Comments = append(m.details.Threads[index].Comments, msg.comment)
+				m.threadIndex = index
+				m.markCurrentThreadRead()
+				break
+			}
+		}
+		m.replyDraft, m.writeThreadID = "", ""
+		m.err = nil
+		m.lastRefresh = time.Now()
 	}
 
 	key, ok := msg.(tea.KeyMsg)
@@ -335,6 +539,9 @@ func (m App) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 		return m, nil
 	}
 	k := key.String()
+	if m.writeMode != writeNone {
+		return m.updateWriteInput(key)
+	}
 	if m.helpVisible {
 		switch k {
 		case "ctrl+c":
@@ -409,6 +616,14 @@ func (m App) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 		return m, nil
 	}
 	switch k {
+	case "c":
+		if m.screen == threadScreen {
+			m.startReply()
+		}
+	case "R":
+		if m.screen == threadScreen {
+			m.startResolveToggle()
+		}
 	case "F":
 		if m.screen == threadScreen {
 			m.searchQuery = ""
@@ -933,6 +1148,9 @@ func (m App) View() string {
 	if m.width == 0 {
 		return "Loading…"
 	}
+	if m.writeMode != writeNone && m.writeMode != writeReply {
+		return m.viewWritePopup()
+	}
 	if m.helpVisible {
 		return m.viewHelp()
 	}
@@ -945,6 +1163,73 @@ func (m App) View() string {
 	return m.viewThreads()
 }
 
+func (m App) viewWritePopup() string {
+	width := max(20, min(76, m.width-4))
+	thread := m.threadByID(m.writeThreadID)
+	location := "selected thread"
+	if thread != nil {
+		location = fmt.Sprintf("%s:%d", thread.Path, thread.Line)
+	}
+	var lines []string
+	switch m.writeMode {
+	case writeReply:
+		lines = []string{
+			titleStyle.Render("Reply to " + location),
+			"",
+		}
+		draft := m.replyDraft + "█"
+		for _, sourceLine := range strings.Split(draft, "\n") {
+			wrapped := ansi.Hardwrap(ansi.Wordwrap(sourceLine, width-2, ""), width-2, false)
+			lines = append(lines, strings.Split(wrapped, "\n")...)
+		}
+		if m.err != nil {
+			lines = append(lines, "", badStyle.Render(m.err.Error()))
+		}
+		lines = append(lines, "", dimStyle.Render("enter newline  •  ctrl-s review  •  esc cancel"))
+	case writeReplyConfirm:
+		lines = []string{titleStyle.Render("Submit this reply to " + location + "?"), ""}
+		lines = append(lines, renderCommentMarkdown(m.replyDraft, width-2)...)
+		lines = append(lines, "", warnStyle.Render("y submit  •  n/esc continue editing"))
+	case writeReplyBusy:
+		lines = []string{titleStyle.Render("Submitting reply…"), "", dimStyle.Render(location)}
+	case writeResolveConfirm:
+		action := "resolve"
+		if !m.resolveTarget {
+			action = "unresolve"
+		}
+		lines = []string{
+			titleStyle.Render(strings.ToUpper(action[:1]) + action[1:] + " " + location + "?"),
+			"",
+			warnStyle.Render("y confirm  •  n/esc cancel"),
+		}
+	case writeResolveBusy:
+		action := "Resolving"
+		if !m.resolveTarget {
+			action = "Unresolving"
+		}
+		lines = []string{titleStyle.Render(action + " thread…"), "", dimStyle.Render(location)}
+	}
+	maxLines := max(3, m.height-4)
+	if len(lines) > maxLines {
+		lines = lines[len(lines)-maxLines:]
+	}
+	for index := range lines {
+		lines[index] = ansi.Truncate(lines[index], width, "")
+	}
+	popup := paneStyle(true).Width(width).Render(strings.Join(lines, "\n"))
+	return lipgloss.Place(m.width, m.height, lipgloss.Center, lipgloss.Center, popup)
+}
+
+func (m App) threadByID(id string) *ReviewThread {
+	for index := range m.details.Threads {
+		if m.details.Threads[index].ID == id {
+			thread := m.details.Threads[index]
+			return &thread
+		}
+	}
+	return nil
+}
+
 type helpBinding struct {
 	key    string
 	action string
@@ -999,18 +1284,13 @@ func (m App) helpBindings() []helpBinding {
 		{"/", "Fuzzy-search file paths and combine status:, author:, and updated:true filters"},
 		{"F", "Clear the active thread filter and show every thread"},
 		{"n / N", "Next / previous new update"},
+		{"c", "Compose a reply to the selected thread"},
+		{"R", "Resolve or unresolve the selected thread"},
 		{"d", "Open pull request dashboard"},
 		{"enter / za", "Fold / expand thread"},
 		{"b / esc", backAction},
 		{"r", "Refresh now"},
 	}
-	for _, item := range writeCapabilities(m.details, m.selectedThread()) {
-		state := item.reason
-		if item.authorized {
-			state = "ready; " + item.reason
-		}
-		bindings = append(bindings, helpBinding{"write", item.name + ": " + state})
-	}
 	bindings = append(bindings,
 		helpBinding{"?", "Close this help"},
 		helpBinding{"q / ctrl-c", "Quit"},
@@ -1477,7 +1757,7 @@ func applicableRulesetCount(rulesets []Ruleset) int {
 
 type writeCapability struct {
 	name, reason string
-	authorized   bool
+	enabled      bool
 }
 
 func writeCapabilities(pr PRDetails, thread *ReviewThread) []writeCapability {
@@ -1491,32 +1771,41 @@ func writeCapabilities(pr PRDetails, thread *ReviewThread) []writeCapability {
 	}
 	threadReason := "select a review thread"
 	canReply, canResolve := false, false
+	resolveName := "resolve thread"
 	if thread != nil {
 		canReply = thread.ViewerCanReply
-		canResolve = thread.ViewerCanResolve || thread.ViewerCanUnresolve
+		if thread.IsResolved {
+			resolveName = "unresolve thread"
+			canResolve = thread.ViewerCanUnresolve
+		} else {
+			canResolve = thread.ViewerCanResolve
+		}
 		threadReason = "GitHub did not grant permission for this thread"
 	}
 	return []writeCapability{
-		capability("reply", canReply, threadReason),
-		capability("resolve / unresolve", canResolve, threadReason),
-		capability("react", pr.Permissions.CanReact, "GitHub did not grant reaction permission"),
-		capability("update branch", pr.Permissions.CanUpdatePR, "GitHub did not grant update permission"),
-		capability("auto-merge", pr.Permissions.CanEnableMerge, "auto-merge is unavailable for this PR"),
+		capability("reply", canReply, threadReason, true),
+		capability(resolveName, canResolve, threadReason, true),
+		capability("react", pr.Permissions.CanReact, "GitHub did not grant reaction permission", false),
+		capability("update branch", pr.Permissions.CanUpdatePR, "GitHub did not grant update permission", false),
+		capability("auto-merge", pr.Permissions.CanEnableMerge, "auto-merge is unavailable for this PR", false),
 	}
 }
 
-func capability(name string, allowed bool, denied string) writeCapability {
-	if allowed {
-		return writeCapability{name: name, authorized: true, reason: "authorized; write UI not implemented"}
+func capability(name string, allowed bool, denied string, implemented bool) writeCapability {
+	if !allowed {
+		return writeCapability{name: name, reason: denied}
 	}
-	return writeCapability{name: name, reason: denied}
+	if !implemented {
+		return writeCapability{name: name, reason: "write action not implemented yet"}
+	}
+	return writeCapability{name: name, enabled: true, reason: "available"}
 }
 
 func writeCapabilityLines(pr PRDetails, thread *ReviewThread) []string {
 	var lines []string
 	for _, item := range writeCapabilities(pr, thread) {
 		marker := badStyle.Render("disabled")
-		if item.authorized {
+		if item.enabled {
 			marker = okStyle.Render("ready")
 		}
 		lines = append(lines, pad(item.name, 21)+" "+marker+"  "+dimStyle.Render(item.reason))
@@ -1585,9 +1874,11 @@ func (m App) viewThreads() string {
 		right := m.threadDetail(rightWidth, contentHeight)
 		body = lipgloss.JoinHorizontal(lipgloss.Top, left, " ", right)
 	}
-	help := "? keys • h/l focus • j/k move/scroll • n/N new • d dashboard • b back • q quit"
+	help := "? keys • h/l focus • j/k move/scroll • c reply • R resolve • d dashboard • b back • q quit"
 	if m.searching {
 		help = "path words • status:open • author:name • updated:true • enter apply • esc cancel"
+	} else if m.writeMode == writeReply {
+		help = "reply inline • enter newline • ctrl-s review • esc cancel"
 	}
 	return m.frame(append(top, body), help)
 }
@@ -1769,6 +2060,37 @@ func (m App) detailLines(width int) []detailLine {
 			lines = append(lines, detailLine{}, detailLine{text: warnStyle.Render("Showing the first 100 comments in this thread.")})
 		}
 	}
+	if m.writeMode == writeReply && m.writeThreadID == thread.ID {
+		lines = append(lines, m.inlineReplyLines(width)...)
+	}
+	return lines
+}
+
+func (m App) inlineReplyLines(width int) []detailLine {
+	rail := warnStyle.Render("│ ")
+	lines := []detailLine{
+		{},
+		{rail: rail, anchor: "reply:header", text: titleStyle.Render("Reply draft")},
+	}
+	draft := m.replyDraft + "█"
+	textWidth := max(1, width-4)
+	lineIndex := 0
+	for _, sourceLine := range strings.Split(draft, "\n") {
+		wrapped := ansi.Hardwrap(ansi.Wordwrap(sourceLine, textWidth, ""), textWidth, false)
+		for _, part := range strings.Split(wrapped, "\n") {
+			lines = append(lines, detailLine{
+				rail: rail, anchor: fmt.Sprintf("reply:body:%d", lineIndex), text: part,
+			})
+			lineIndex++
+		}
+	}
+	if m.err != nil {
+		lines = append(lines, detailLine{rail: rail, text: badStyle.Render(m.err.Error())})
+	}
+	lines = append(lines, detailLine{
+		rail: rail,
+		text: dimStyle.Render("enter newline  •  ctrl-s review  •  esc cancel"),
+	})
 	return lines
 }
 
diff --git a/tui_test.go b/tui_test.go
index a272ed6..ba07a03 100644
--- a/tui_test.go
+++ b/tui_test.go
@@ -13,9 +13,29 @@ import (
 )
 
 type recordingService struct {
-	owner  string
-	repo   string
-	number int
+	owner         string
+	repo          string
+	number        int
+	writeThreadID string
+	writeBody     string
+	writeResolved bool
+}
+
+func (s *recordingService) SetThreadResolved(
+	_ context.Context, threadID string, resolved bool,
+) (ReviewThread, error) {
+	s.writeThreadID, s.writeResolved = threadID, resolved
+	return ReviewThread{
+		ID: threadID, IsResolved: resolved,
+		ViewerCanResolve: !resolved, ViewerCanUnresolve: resolved, ViewerCanReply: true,
+	}, nil
+}
+
+func (s *recordingService) ReplyToThread(
+	_ context.Context, threadID, body string,
+) (ReviewComment, error) {
+	s.writeThreadID, s.writeBody = threadID, body
+	return ReviewComment{ID: "new-comment", Author: "me", Body: body}, nil
 }
 
 func (s *recordingService) ListPullRequests(context.Context, string, string, int, bool) ([]PullRequest, error) {
@@ -437,16 +457,106 @@ func TestDetailRefreshKeepsLogicalCommentAnchored(t *testing.T) {
 
 func TestWriteCapabilityGateExplainsCachedAndPermissionStates(t *testing.T) {
 	cached := writeCapabilities(PRDetails{FromCache: true}, nil)
-	if cached[0].reason != "offline cached snapshot" || cached[0].authorized {
+	if cached[0].reason != "offline cached snapshot" || cached[0].enabled {
 		t.Fatalf("cached capability = %#v", cached[0])
 	}
 	thread := &ReviewThread{ViewerCanReply: true}
 	live := writeCapabilities(PRDetails{Permissions: ViewerPermissions{CanReact: true}}, thread)
-	if !live[0].authorized || live[1].authorized || !live[2].authorized {
+	if !live[0].enabled || live[1].enabled || live[2].enabled {
 		t.Fatalf("live capabilities = %#v", live)
 	}
 }
 
+func TestReplyComposerConfirmsAndAddsReturnedComment(t *testing.T) {
+	service := &recordingService{}
+	m := NewApp(service, "o", "r", false, 50, time.Second)
+	m.screen, m.loading = threadScreen, false
+	m.details = PRDetails{
+		PullRequest: PullRequest{ID: "pr", Owner: "o", Repository: "r", Number: 1},
+		Threads: []ReviewThread{{
+			ID: "thread", ViewerCanReply: true, Comments: []ReviewComment{{ID: "old"}},
+		}},
+	}
+
+	updated, _ := m.Update(tea.KeyMsg{Type: tea.KeyRunes, Runes: []rune("c")})
+	m = updated.(App)
+	if m.writeMode != writeReply {
+		t.Fatalf("reply key opened mode %d", m.writeMode)
+	}
+	updated, _ = m.Update(tea.KeyMsg{Type: tea.KeyRunes, Runes: []rune("hello")})
+	m = updated.(App)
+	updated, _ = m.Update(tea.KeyMsg{Type: tea.KeyCtrlS})
+	m = updated.(App)
+	if m.writeMode != writeReplyConfirm {
+		t.Fatalf("ctrl-s opened mode %d", m.writeMode)
+	}
+	updated, command := m.Update(tea.KeyMsg{Type: tea.KeyRunes, Runes: []rune("y")})
+	m = updated.(App)
+	if command == nil || m.writeMode != writeReplyBusy {
+		t.Fatalf("reply confirmation produced mode=%d command=%v", m.writeMode, command)
+	}
+	updated, _ = m.Update(command())
+	m = updated.(App)
+	if service.writeThreadID != "thread" || service.writeBody != "hello" ||
+		len(m.details.Threads[0].Comments) != 2 ||
+		m.details.Threads[0].Comments[1].ID != "new-comment" {
+		t.Fatalf("reply was not applied: service=%#v model=%#v", service, m.details.Threads[0])
+	}
+}
+
+func TestReplyComposerRendersInlineWithCurrentThread(t *testing.T) {
+	service := &recordingService{}
+	m := NewApp(service, "o", "r", false, 50, time.Second)
+	m.screen, m.loading, m.width, m.height = threadScreen, false, 100, 24
+	m.details = PRDetails{
+		PullRequest: PullRequest{ID: "pr", Owner: "o", Repository: "r", Number: 1},
+		Threads: []ReviewThread{{
+			ID: "thread", Path: "main.go", Line: 12, ViewerCanReply: true,
+			Comments: []ReviewComment{{
+				ID: "existing", Author: "reviewer", Body: "Existing review context",
+			}},
+		}},
+	}
+
+	updated, _ := m.Update(tea.KeyMsg{Type: tea.KeyRunes, Runes: []rune("c")})
+	m = updated.(App)
+	plain := ansi.Strip(m.View())
+	for _, wanted := range []string{"Existing review context", "Reply draft", "ctrl-s review"} {
+		if !strings.Contains(plain, wanted) {
+			t.Fatalf("inline reply view is missing %q:\n%s", wanted, plain)
+		}
+	}
+	if m.focus != threadDetailPane {
+		t.Fatal("inline reply did not focus the thread detail pane")
+	}
+}
+
+func TestResolveToggleConfirmsAndUsesCurrentThreadState(t *testing.T) {
+	service := &recordingService{}
+	m := NewApp(service, "o", "r", false, 50, time.Second)
+	m.screen, m.loading = threadScreen, false
+	m.details = PRDetails{
+		PullRequest: PullRequest{ID: "pr", Owner: "o", Repository: "r", Number: 1},
+		Threads: []ReviewThread{{
+			ID: "thread", ViewerCanResolve: true,
+		}},
+	}
+
+	updated, _ := m.Update(tea.KeyMsg{Type: tea.KeyRunes, Runes: []rune("R")})
+	m = updated.(App)
+	if m.writeMode != writeResolveConfirm || !m.resolveTarget {
+		t.Fatalf("resolve key produced mode=%d target=%t", m.writeMode, m.resolveTarget)
+	}
+	updated, command := m.Update(tea.KeyMsg{Type: tea.KeyRunes, Runes: []rune("y")})
+	m = updated.(App)
+	updated, _ = m.Update(command())
+	m = updated.(App)
+	if !service.writeResolved || !m.details.Threads[0].IsResolved ||
+		!m.details.Threads[0].ViewerCanUnresolve {
+		t.Fatalf("thread was not resolved: service=%#v thread=%#v", service, m.details.Threads[0])
+	}
+}
+
 func TestPollingMarksNewThreadCommentsUnread(t *testing.T) {
 	m := NewApp(nil, "o", "r", false, 50, 10*time.Second)
 	m.screen = threadScreen
@@ -546,7 +656,7 @@ func TestHelpCanScrollInShortTerminal(t *testing.T) {
 	}
 }
 
-func TestHelpWrapsLongActionsAndExplainsFilterClear(t *testing.T) {
+func TestHelpWrapsLongActionsWithoutCapabilityStatus(t *testing.T) {
 	m := NewApp(nil, "o", "r", false, 50, 10*time.Second)
 	m.screen, m.width, m.height = threadScreen, 46, 20
 	rows := m.helpRows(m.helpContentWidth())
@@ -554,8 +664,10 @@ func TestHelpWrapsLongActionsAndExplainsFilterClear(t *testing.T) {
 	if !strings.Contains(plain, "Clear the active thread filter and show every thread") {
 		t.Fatalf("F binding is not explained clearly:\n%s", plain)
 	}
-	if !strings.Contains(plain, "GitHub did not grant update permission") {
-		t.Fatalf("long capability explanation was cut off:\n%s", plain)
+	if strings.Contains(plain, "write action") ||
+		strings.Contains(plain, "GitHub did not grant") ||
+		strings.Contains(plain, "available") {
+		t.Fatalf("write capability status leaked into keybinding help:\n%s", plain)
 	}
 	for index, row := range rows {
 		if width := ansi.StringWidth(row); width > m.helpContentWidth() {