feat(tui): add centered session width

packages/tui/src/component/dialog-config.tsx

@@ -60,6 +60,15 @@ export const settings: Setting[] = [
     labels: ["off", "on"],
     keywords: ["scroll bar"],
   },
+  {
+    title: "Max width",
+    category: "Session",
+    path: ["session", "max_width"],
+    default: "auto",
+    values: ["auto", 80, 100, 120],
+    labels: ["auto", "80 columns", "100 columns", "120 columns"],
+    keywords: ["transcript", "composer", "centered", "reading width"],
+  },
   {
     title: "Thinking",
     category: "Session",

packages/tui/src/config/index.tsx

@@ -125,6 +125,11 @@ export const Info = Schema.Struct({
         description: "Session sidebar visibility; 'auto' shows it when space permits",
       }),
       scrollbar: Schema.optional(Schema.Boolean).annotate({ description: "Show the session transcript scrollbar" }),
+      max_width: Schema.optional(
+        Schema.Union([Schema.Int.check(Schema.isGreaterThan(4)), Schema.Literal("auto")]),
+      ).annotate({
+        description: "Session transcript and composer max width, or 'auto' to use the available width",
+      }),
       thinking: Schema.optional(Schema.Literals(["show", "hide"])).annotate({
         description: "Show or hide model reasoning by default",
       }),

packages/tui/src/routes/session/index.tsx

@@ -68,7 +68,7 @@ import { errorMessage } from "../../util/error"
 import { useToast } from "../../ui/toast"
 import stripAnsi from "strip-ansi"
 import { usePromptRef } from "../../context/prompt"
-import { sessionTabsFitVertically, SESSION_SIDEBAR_WIDTH } from "../../ui/layout"
+import { sessionContentWidth, sessionTabsFitVertically, SESSION_SIDEBAR_WIDTH } from "../../ui/layout"
 import { projectedPromptInput } from "../../prompt/codec"
 import { deduplicateVisibleImages } from "../../prompt/attachment"
 import { useEpilogue } from "../../context/epilogue"
@@ -225,6 +225,7 @@ export function Session() {
   const thinkingMode = createMemo<ThinkingMode>(() => config.session?.thinking ?? "hide")
   const showThinking = createMemo(() => true)
   const showScrollbar = createMemo(() => config.session?.scrollbar ?? false)
+  const maxWidth = createMemo(() => config.session?.max_width ?? "auto")
   const markdownMode = createMemo(() => config.session?.markdown ?? "rendered")
   const diffWrapMode = createMemo(() => config.diffs?.wrap ?? "word")
   const groupExploration = createMemo(() => config.session?.grouping !== "none")
@@ -243,7 +244,7 @@ export function Session() {
     if (sidebar() === "auto" && wide()) return true
     return false
   })
-  const contentWidth = createMemo(() => availableWidth() - (sidebarVisible() ? 42 : 0) - 4)
+  const contentWidth = createMemo(() => sessionContentWidth(availableWidth(), sidebarVisible(), maxWidth()))
   const models = createMemo(() => data.location.model.list(location()) ?? [])
 
   const scrollAcceleration = createMemo(() => getScrollAcceleration(config))
@@ -1037,103 +1038,107 @@ export function Session() {
       }}
     >
       <box flexDirection="row" flexGrow={1} minHeight={0}>
-        <box
-          flexGrow={1}
-          minHeight={0}
-          paddingBottom={1}
-          paddingLeft={dimensions().width < 44 ? 1 : 2}
-          paddingRight={dimensions().width < 44 ? 1 : 2}
-          gap={1}
-        >
-          <Show when={session()}>
-            <scrollbox
-              ref={(r) => (scroll = r)}
-              viewportOptions={{
-                paddingRight: showScrollbar() ? 1 : 0,
-              }}
-              verticalScrollbarOptions={{
-                paddingLeft: 1,
-                visible: showScrollbar(),
-                trackOptions: {
-                  backgroundColor: theme.raise(theme.background.surface.offset),
-                  foregroundColor: theme.border.default,
-                },
-              }}
-              stickyScroll={!navigationMessage()}
-              stickyStart="bottom"
-              flexGrow={1}
-              scrollAcceleration={scrollAcceleration()}
-            >
-              <For each={visibleRows()}>
-                {(row, index) => (
-                  <SessionRowView
-                    row={row}
-                    message={(messageID) => data.session.message.get(route.sessionID, messageID)}
-                    boundaryID={boundaries()[index() + hidden()]}
+        <box flexGrow={1} minHeight={0} alignItems="center">
+          <box
+            width="100%"
+            maxWidth={maxWidth() === "auto" ? undefined : maxWidth()}
+            flexGrow={1}
+            minHeight={0}
+            paddingBottom={1}
+            paddingLeft={dimensions().width < 44 ? 1 : 2}
+            paddingRight={dimensions().width < 44 ? 1 : 2}
+            gap={1}
+          >
+            <Show when={session()}>
+              <scrollbox
+                ref={(r) => (scroll = r)}
+                viewportOptions={{
+                  paddingRight: showScrollbar() ? 1 : 0,
+                }}
+                verticalScrollbarOptions={{
+                  paddingLeft: 1,
+                  visible: showScrollbar(),
+                  trackOptions: {
+                    backgroundColor: theme.raise(theme.background.surface.offset),
+                    foregroundColor: theme.border.default,
+                  },
+                }}
+                stickyScroll={!navigationMessage()}
+                stickyStart="bottom"
+                flexGrow={1}
+                scrollAcceleration={scrollAcceleration()}
+              >
+                <For each={visibleRows()}>
+                  {(row, index) => (
+                    <SessionRowView
+                      row={row}
+                      message={(messageID) => data.session.message.get(route.sessionID, messageID)}
+                      boundaryID={boundaries()[index() + hidden()]}
+                    />
+                  )}
+                </For>
+                <BackgroundToolHint messages={messages()} />
+                <Show when={session()?.revert?.messageID}>
+                  <RevertMessage
+                    count={messagesFromRevert().filter((message) => message.type === "user").length}
+                    files={session()!.revert!.files ?? []}
                   />
-                )}
-              </For>
-              <BackgroundToolHint messages={messages()} />
-              <Show when={session()?.revert?.messageID}>
-                <RevertMessage
-                  count={messagesFromRevert().filter((message) => message.type === "user").length}
-                  files={session()!.revert!.files ?? []}
+                </Show>
+                <Show when={navigationSlack()}>
+                  {(height) => <box id={NAVIGATION_SLACK_ID} height={height()} flexShrink={0} />}
+                </Show>
+              </scrollbox>
+              <box flexShrink={0}>
+                <Show when={!composer.open && !disabled() && queuedPrompts().length > 0}>
+                  <QueuedPromptDock prompts={queuedPrompts()} onOpen={openQueuedPrompts} />
+                </Show>
+                <PluginSlot name="session.composer.top" input={{ sessionID: route.sessionID }} mode="all" />
+                <Composer
+                  sessionID={route.sessionID}
+                  open={composer.open || (!!session()?.parentID && forms().length === 0)}
+                  defaultTab={composer.tab ?? (session()?.parentID ? "subagents" : undefined)}
+                  onClose={() => setComposer("open", false)}
                 />
-              </Show>
-              <Show when={navigationSlack()}>
-                {(height) => <box id={NAVIGATION_SLACK_ID} height={height()} flexShrink={0} />}
-              </Show>
-            </scrollbox>
-            <box flexShrink={0}>
-              <Show when={!composer.open && !disabled() && queuedPrompts().length > 0}>
-                <QueuedPromptDock prompts={queuedPrompts()} onOpen={openQueuedPrompts} />
-              </Show>
-              <PluginSlot name="session.composer.top" input={{ sessionID: route.sessionID }} mode="all" />
-              <Composer
-                sessionID={route.sessionID}
-                open={composer.open || (!!session()?.parentID && forms().length === 0)}
-                defaultTab={composer.tab ?? (session()?.parentID ? "subagents" : undefined)}
-                onClose={() => setComposer("open", false)}
-              />
-              <Switch>
-                <Match when={composer.open || (!!session()?.parentID && forms().length === 0)}>{null}</Match>
-                <Match when={promptedPermissions().length > 0}>
-                  <Show when={promptedPermissions()[0]?.id} keyed>
-                    {(_) => {
-                      const request = promptedPermissions()[0]
-                      return request ? (
-                        <PermissionPrompt request={request} directory={session()?.location.directory} />
-                      ) : null
-                    }}
-                  </Show>
-                </Match>
-                <Match when={forms().length > 0}>
-                  <Show when={forms()[0]?.id} keyed>
-                    {(_) => {
-                      const form = forms()[0]
-                      return form ? <FormPrompt form={form} /> : null
-                    }}
-                  </Show>
-                </Match>
-                <Match when={!disabled()}>
-                  <Prompt
-                    visible={true}
-                    ref={bind}
-                    disabled={false}
-                    onSubmit={() => {
-                      toBottom()
-                    }}
-                    onEmptySubmit={async () => {
-                      const next = queuedPrompts()[0]
-                      if (!next) return false
-                      return mutatePending("steer", next.id)
-                    }}
-                    sessionID={route.sessionID}
-                  />
-                </Match>
-              </Switch>
-            </box>
-          </Show>
+                <Switch>
+                  <Match when={composer.open || (!!session()?.parentID && forms().length === 0)}>{null}</Match>
+                  <Match when={promptedPermissions().length > 0}>
+                    <Show when={promptedPermissions()[0]?.id} keyed>
+                      {(_) => {
+                        const request = promptedPermissions()[0]
+                        return request ? (
+                          <PermissionPrompt request={request} directory={session()?.location.directory} />
+                        ) : null
+                      }}
+                    </Show>
+                  </Match>
+                  <Match when={forms().length > 0}>
+                    <Show when={forms()[0]?.id} keyed>
+                      {(_) => {
+                        const form = forms()[0]
+                        return form ? <FormPrompt form={form} /> : null
+                      }}
+                    </Show>
+                  </Match>
+                  <Match when={!disabled()}>
+                    <Prompt
+                      visible={true}
+                      ref={bind}
+                      disabled={false}
+                      onSubmit={() => {
+                        toBottom()
+                      }}
+                      onEmptySubmit={async () => {
+                        const next = queuedPrompts()[0]
+                        if (!next) return false
+                        return mutatePending("steer", next.id)
+                      }}
+                      sessionID={route.sessionID}
+                    />
+                  </Match>
+                </Switch>
+              </box>
+            </Show>
+          </box>
         </box>
         <Show when={sidebarVisible()}>
           <Switch>

packages/tui/src/ui/layout.ts

@@ -1,6 +1,13 @@
 export const SESSION_SIDEBAR_WIDTH = 42
 const SESSION_CONTENT_MIN_WIDTH = 44
+const SESSION_CONTENT_PADDING = 4
 
 export function sessionTabsFitVertically(total: number) {
   return total >= SESSION_SIDEBAR_WIDTH + SESSION_CONTENT_MIN_WIDTH
 }
+
+export function sessionContentWidth(total: number, sidebar: boolean, maxWidth: number | "auto" = "auto") {
+  const available = total - (sidebar ? SESSION_SIDEBAR_WIDTH : 0) - SESSION_CONTENT_PADDING
+  if (maxWidth === "auto") return available
+  return Math.max(1, Math.min(available, maxWidth - SESSION_CONTENT_PADDING))
+}

packages/tui/test/config-v2.test.tsx

@@ -27,6 +27,15 @@ test("validates the session tabs setting", () => {
   expect(decode({ session: { image_preview: true } })).toEqual({ session: { image_preview: true } })
 })
 
+test("validates the session max width setting", () => {
+  const decode = Schema.decodeUnknownSync(Info)
+
+  expect(decode({ session: { max_width: "auto" } })).toEqual({ session: { max_width: "auto" } })
+  expect(decode({ session: { max_width: 100 } })).toEqual({ session: { max_width: 100 } })
+  expect(() => decode({ session: { max_width: 4 } })).toThrow()
+  expect(() => decode({ session: { max_width: 100.5 } })).toThrow()
+})
+
 test("resolves nested config and keybind defaults", () => {
   const config = resolve(
     {
@@ -53,6 +62,13 @@ test("shows resolved tab defaults in settings", () => {
   expect(settings.find((setting) => setting.path.join(".") === "tabs.layout")?.default).toBe("horizontal")
 })
 
+test("shows session max width presets in settings", () => {
+  const setting = settings.find((setting) => setting.path.join(".") === "session.max_width")
+
+  expect(setting?.default).toBe("auto")
+  expect(setting?.values).toEqual(["auto", 80, 100, 120])
+})
+
 test("provides config and its host interface", async () => {
   const config = resolve({}, { terminalSuspend: true })
   let current = {}

packages/tui/test/ui/layout.test.ts

@@ -1,8 +1,18 @@
 import { expect, test } from "bun:test"
-import { sessionTabsFitVertically, SESSION_SIDEBAR_WIDTH } from "../../src/ui/layout"
+import { sessionContentWidth, sessionTabsFitVertically, SESSION_SIDEBAR_WIDTH } from "../../src/ui/layout"
 
 test("vertical tabs match the session sidebar and preserve compact content width", () => {
   expect(SESSION_SIDEBAR_WIDTH).toBe(42)
   expect(sessionTabsFitVertically(86)).toBe(true)
   expect(sessionTabsFitVertically(85)).toBe(false)
 })
+
+test("session content uses available width by default", () => {
+  expect(sessionContentWidth(160, false)).toBe(156)
+  expect(sessionContentWidth(160, true)).toBe(114)
+})
+
+test("session content caps wide sessions and preserves narrow sessions", () => {
+  expect(sessionContentWidth(160, false, 100)).toBe(96)
+  expect(sessionContentWidth(80, false, 100)).toBe(76)
+})