feat(terminal): bound command block output

src/lib/components/CommandBlockSettings.svelte

@@ -4,13 +4,23 @@
   import { errMsg, t } from "../i18n/index.svelte.ts";
   import { toast } from "../stores/toast.svelte.ts";
   import type { CommandBlockRedactRule } from "../stores/app.svelte.ts";
+  import {
+    COMMAND_BLOCK_MAX_LINES_DEFAULT,
+    COMMAND_BLOCK_MAX_LINES_MAX,
+    COMMAND_BLOCK_MAX_LINES_MIN,
+    TERMINAL_SCROLLBACK_LINES,
+  } from "../terminal/limits.ts";
 
   let commandBlockBar = $state(true);
   let autoColorBlocks = $state(false);
   let splitMode = $state<app.CommandBlockSplitMode>("enter");
   let splitModeReady = $state(false);
   let splitModeSaving = $state(false);
   let splitModeNote = $state<string | null>(null);
+  let maxLines = $state(COMMAND_BLOCK_MAX_LINES_DEFAULT);
+  let maxLinesReady = $state(false);
+  let maxLinesSaving = $state(false);
+  let maxLinesNote = $state<string | null>(null);
   let promptEnabled = $state(true);
   let promptReplacement = $state("anonymous@rssh");
   let redactRules = $state<CommandBlockRedactRule[]>([]);
@@ -25,15 +35,18 @@
   let confirmRuleDeleteTimer: number | null = null;
 
   onMount(async () => {
-    const [bar, autoColor, loadedSplitMode] = await Promise.all([
+    const [bar, autoColor, loadedSplitMode, loadedMaxLines] = await Promise.all([
       app.loadCommandBlockBar(),
       app.loadAutoColorBlocks(),
       app.loadCommandBlockSplitMode(),
+      app.loadCommandBlockMaxLines(),
     ]);
     commandBlockBar = bar;
     autoColorBlocks = autoColor;
     splitMode = loadedSplitMode;
     splitModeReady = true;
+    maxLines = loadedMaxLines;
+    maxLinesReady = true;
     try {
       applyRedaction(await app.loadCommandBlockRedaction(true));
       redactionReady = true;
@@ -79,6 +92,23 @@
     }
   }
 
+  async function saveMaxLines() {
+    if (!maxLinesReady || maxLinesSaving) return;
+    const previous = app.commandBlockMaxLines();
+    maxLinesSaving = true;
+    maxLinesNote = null;
+    try {
+      await app.setCommandBlockMaxLines(maxLines);
+      maxLines = app.commandBlockMaxLines();
+    } catch (error) {
+      maxLines = previous;
+      maxLinesNote = t("settings.shell.command_block_max_lines_error", { error: errMsg(error) });
+      toast.error(errMsg(error));
+    } finally {
+      maxLinesSaving = false;
+    }
+  }
+
   async function savePromptEnabled() {
     const previous = !promptEnabled;
     savingPrompt = true;
@@ -242,6 +272,40 @@
         {/if}
       </fieldset>
 
+      <div class="card-divider"></div>
+      <div class="cmd-block-head">
+        <div class="cmd-block-head-body">
+          <label class="cmd-block-title" for="command-block-max-lines">
+            {t("settings.shell.command_block_max_lines")}
+          </label>
+          <div id="command-block-max-lines-desc" class="cmd-block-desc">
+            {t("settings.shell.command_block_max_lines_desc", {
+              min: COMMAND_BLOCK_MAX_LINES_MIN,
+              max: COMMAND_BLOCK_MAX_LINES_MAX,
+              scrollback: TERMINAL_SCROLLBACK_LINES,
+            })}
+          </div>
+          <div class="cmd-block-desc">{t("settings.shell.command_block_max_lines_new_sessions")}</div>
+          {#if maxLinesNote}
+            <div class="inline-error" role="alert">{maxLinesNote}</div>
+          {/if}
+        </div>
+        <input
+          id="command-block-max-lines"
+          class="max-lines-input"
+          type="number"
+          bind:value={maxLines}
+          min={COMMAND_BLOCK_MAX_LINES_MIN}
+          max={COMMAND_BLOCK_MAX_LINES_MAX}
+          disabled={!maxLinesReady || maxLinesSaving}
+          aria-describedby="command-block-max-lines-desc"
+          onblur={saveMaxLines}
+          onkeydown={(event) => {
+            if (event.key === "Enter") (event.currentTarget as HTMLInputElement).blur();
+          }}
+        />
+      </div>
+
       <div class="card-divider"></div>
       <div class="cmd-block-head">
         <div class="cmd-block-head-body">
@@ -496,6 +560,11 @@
     white-space: nowrap;
   }
   .inline-error { margin-top: 8px; color: var(--error); font-size: 11px; line-height: 1.5; }
+  .max-lines-input {
+    width: 88px;
+    flex: 0 0 auto;
+    font-variant-numeric: tabular-nums;
+  }
 
   /* 卡片内分隔线：负边距贯穿到卡片左右边缘。 */
   .card-divider {

src/lib/components/TerminalPane.svelte

@@ -19,6 +19,7 @@
     import {createCommandBlockTracker, type CommandBlock, type CommandBlockTracker} from "../terminal/command-blocks.ts";
     import {readViewportSnapshot, readViewportText} from "../terminal/viewport-snapshot.ts";
     import {createFoldStore, type FoldStore} from "../terminal/folds.ts";
+    import {TERMINAL_SCROLLBACK_LINES, commandBlockFoldCacheLines} from "../terminal/limits.ts";
     import {createPaintScheduler, type PaintScheduler} from "../terminal/paint-scheduler.ts";
 
     import {extractBlockTexts, extractBlocksText} from "../terminal/block-content.ts";
@@ -230,14 +231,16 @@
     function fitTerminal() {
         if (destroyed || !terminal) return;
         // saved fold lines have the current column geometry. Expand them before
-        // FitAddon calls terminal.resize(), including while the alt buffer is
-        // active; FoldStore itself is bound to the normal history buffer.
+        // FitAddon calls terminal.resize(), then reapply the automatic limit to
+        // the reflowed rows. This also runs while the alt buffer is active;
+        // FoldStore itself is bound to the normal history buffer and defers the
+        // re-fold until the normal buffer becomes active again.
         const proposed = fitAddon?.proposeDimensions();
-        if (proposed && terminal
-            && (proposed.cols !== terminal.cols || proposed.rows !== terminal.rows)) {
-            foldStore?.unfoldAll();
-        }
+        const dimensionsChanged = !!proposed
+            && (proposed.cols !== terminal.cols || proposed.rows !== terminal.rows);
+        if (dimensionsChanged) foldStore?.unfoldAll();
         fitAddon?.fit();
+        if (dimensionsChanged) foldStore?.enforceAutoFold();
     }
 
     function writeRawOutput(raw: Uint8Array) {
@@ -278,17 +281,17 @@
         const out: BlockRect[] = [];
         for (const b of blockTracker.blocks) {
             if (b.start.isDisposed) continue;
-            const folded = foldStore?.isFolded(b.id) ?? false;
-            // Folded：竖线只标 prompt 行，body 已不在 buffer。
-            // Unfolded：常规 [start..end] 跨度。
+            const fold = foldStore?.getFold(b.id);
+            const folded = fold !== undefined;
+            // Full fold leaves only the command row. An automatic prefix fold
+            // keeps the newest output rows visible, so its bar still spans them.
             const startLine = b.start.line;
-            const endLine = folded
+            const endLine = fold?.kind === "full"
                 ? b.start.line
                 : b.end && !b.end.isDisposed ? b.end.line : cursorAbs;
             const top = Math.max(startLine, viewportY);
             const bot = Math.min(endLine, viewportY + rows - 1);
             if (top > bot) continue;
-            const fold = folded ? foldStore?.getFold(b.id) : undefined;
             out.push({
                 id: b.id,
                 y: (top - viewportY) * rowHeight,
@@ -1466,6 +1469,7 @@
     onMount(async () => {
         terminal = new Terminal({
             cursorBlink: true,
+            scrollback: TERMINAL_SCROLLBACK_LINES,
             fontSize: theme.termFontSize(),
             fontFamily: theme.currentTermFontStack(),
             allowProposedApi: true,
@@ -1606,7 +1610,10 @@
         // A tracker keeps one split strategy for its complete lifetime. Changing
         // the preference therefore affects new terminal panes without rewriting
         // existing markers, folds, selections, or colored blocks.
-        const commandBlockSplitMode = await app.loadCommandBlockSplitMode();
+        const [commandBlockSplitMode, commandBlockMaxLines] = await Promise.all([
+            app.loadCommandBlockSplitMode(),
+            app.loadCommandBlockMaxLines(),
+        ]);
         if (destroyed) return;
         blockTracker = createCommandBlockTracker(terminal, commandBlockSplitMode);
         blockTracker.onChange(() => {
@@ -1629,7 +1636,11 @@
 
         // Fold store — splice-based fold/unfold with auto-cleanup on resize and
         // scrollback trim. See folds.ts for the invariant analysis.
-        foldStore = createFoldStore(terminal, blockTracker);
+        foldStore = createFoldStore(terminal, blockTracker, {
+            maxVisibleLines: commandBlockMaxLines,
+            maxCachedLines: commandBlockFoldCacheLines(commandBlockMaxLines),
+            shouldAutoFold: () => app.commandBlockBar(),
+        });
         paintScheduler = createPaintScheduler({
             shouldPaint: () => app.commandBlockBar() && !isAltBuffer,
             paint: () => { paintTick++; },
@@ -1639,6 +1650,7 @@
         terminal.onRender(schedulePaintTick);
         terminal.buffer.onBufferChange((buf) => {
             isAltBuffer = buf.type === "alternate";
+            if (!isAltBuffer) foldStore?.enforceAutoFold();
             paintTick++;
         });
 
@@ -1709,8 +1721,10 @@
     // without us writing paintTick here (writing it here would make this
     // effect self-dependent via `++`, causing an update loop).
     $effect(() => {
-        app.commandBlockBar(); // subscribe
+        const visible = app.commandBlockBar();
+        if (!visible) foldStore?.unfoldAll();
         fitTerminal();
+        if (visible) foldStore?.enforceAutoFold();
     });
 
     // Focus terminal + register writer when this tab becomes active.

src/lib/i18n/locales/en.ts

@@ -189,6 +189,10 @@ const en = {
   "settings.shell.command_block_split_prompt_desc": "Split when a command finishes and a shell prompt is recognized. Custom prompts may be missed; prompt-like output may be mistaken for one.",
   "settings.shell.command_block_split_new_sessions": "Changes apply to newly opened terminals; existing command blocks are not rewritten.",
   "settings.shell.command_block_split_error": "Failed to save the command-block boundary: {error}",
+  "settings.shell.command_block_max_lines": "MAXIMUM OUTPUT LINES",
+  "settings.shell.command_block_max_lines_desc": "Keep the newest output rows visible ({min}–{max}). Older rows fold automatically; visible and cached rows stay below xterm's {scrollback}-row history limit.",
+  "settings.shell.command_block_max_lines_new_sessions": "Changes apply to newly opened terminals.",
+  "settings.shell.command_block_max_lines_error": "Failed to save the command-block line limit: {error}",
   "settings.shell.command_block_auto_color": "Auto-color blocks",
   "settings.shell.command_block_auto_color_desc": "Automatically color every new command block — no right-click needed. You can still right-click to uncolor a specific block.",
   "settings.shell.command_block_tips_title": "Tips",

src/lib/i18n/locales/zh.ts

@@ -191,6 +191,10 @@ const zh: Messages = {
   "settings.shell.command_block_split_prompt_desc": "命令结束并识别到 shell Prompt 时切分。自定义 Prompt 可能漏识别，形似 Prompt 的输出可能误识别。",
   "settings.shell.command_block_split_new_sessions": "更改仅对新打开的终端生效，现有命令块不会被重写。",
   "settings.shell.command_block_split_error": "保存命令块切分方式失败：{error}",
+  "settings.shell.command_block_max_lines": "最大输出行数",
+  "settings.shell.command_block_max_lines_desc": "保留最新的输出行（{min}–{max}）。超限后自动折叠最早的行；可见行与缓存行之和严格小于 xterm 的 {scrollback} 行历史上限。",
+  "settings.shell.command_block_max_lines_new_sessions": "更改仅对新打开的终端生效。",
+  "settings.shell.command_block_max_lines_error": "保存命令块最大行数失败：{error}",
   "settings.shell.command_block_auto_color": "自动染色",
   "settings.shell.command_block_auto_color_desc": "每个新命令块自动染色，无需右键。右键仍可取消单个命令块的染色。",
   "settings.shell.command_block_tips_title": "操作提示",

src/lib/stores/app.svelte.test.ts

@@ -526,3 +526,33 @@ describe("command block split mode", () => {
     });
   });
 });
+
+describe("command block line limit", () => {
+  it("uses the safe default when unset and persists a user value", async () => {
+    invokeMock.mockResolvedValueOnce(null);
+    const app = await loadAppModule();
+
+    await expect(app.loadCommandBlockMaxLines()).resolves.toBe(50);
+    await app.setCommandBlockMaxLines(320);
+
+    expect(app.commandBlockMaxLines()).toBe(320);
+    expect(invokeMock).toHaveBeenCalledWith("set_setting", {
+      key: "command_block_max_lines",
+      value: "320",
+    });
+  });
+
+  it("clamps imported and user-entered values to the supported range", async () => {
+    invokeMock.mockResolvedValueOnce("50000");
+    const app = await loadAppModule();
+
+    await expect(app.loadCommandBlockMaxLines()).resolves.toBe(900);
+    await app.setCommandBlockMaxLines(1);
+
+    expect(app.commandBlockMaxLines()).toBe(10);
+    expect(invokeMock).toHaveBeenCalledWith("set_setting", {
+      key: "command_block_max_lines",
+      value: "10",
+    });
+  });
+});

src/lib/stores/app.svelte.ts

@@ -7,6 +7,10 @@ import type {
   CommandBlockRedactionSettings as RedactionSettings,
 } from "../terminal/command-block-redaction.ts";
 import type { CommandBlockSplitMode } from "../terminal/command-blocks.ts";
+import {
+  COMMAND_BLOCK_MAX_LINES_DEFAULT,
+  normalizeCommandBlockMaxLines,
+} from "../terminal/limits.ts";
 import type { ViewportSnapshot } from "../terminal/viewport-snapshot.ts";
 import { toast } from "./toast.svelte.ts";
 
@@ -753,6 +757,39 @@ export async function setCommandBlockSplitMode(value: CommandBlockSplitMode) {
   _cbsmLoaded = true;
 }
 
+let _commandBlockMaxLines = $state(COMMAND_BLOCK_MAX_LINES_DEFAULT);
+let _cbmlLoaded = false;
+let _cbmlLoad: Promise<number> | null = null;
+export function commandBlockMaxLines() { return _commandBlockMaxLines; }
+export async function loadCommandBlockMaxLines(): Promise<number> {
+  if (_cbmlLoaded) return _commandBlockMaxLines;
+  if (!_cbmlLoad) {
+    _cbmlLoad = (async () => {
+      try {
+        const value = await invoke<string | null>("get_setting", { key: "command_block_max_lines" });
+        _commandBlockMaxLines = value === null
+          ? COMMAND_BLOCK_MAX_LINES_DEFAULT
+          : normalizeCommandBlockMaxLines(value);
+      } catch (error) {
+        console.warn("[settings] command-block line limit load failed:", error);
+        toast.error(errMsg(error));
+      }
+      _cbmlLoaded = true;
+      return _commandBlockMaxLines;
+    })();
+  }
+  return _cbmlLoad;
+}
+export async function setCommandBlockMaxLines(value: number) {
+  const normalized = normalizeCommandBlockMaxLines(value);
+  await invoke("set_setting", {
+    key: "command_block_max_lines",
+    value: String(normalized),
+  });
+  _commandBlockMaxLines = normalized;
+  _cbmlLoaded = true;
+}
+
 let _commandBlockBar = $state(true);
 let _cbbLoaded = false;
 export function commandBlockBar() { return _commandBlockBar; }

src/lib/terminal/block-content.test.ts

@@ -307,6 +307,24 @@ describe("resolveBlockLines (folded blocks)", () => {
     const lines = resolveBlockLines(term as any, fakeBlock(1, 0, 1), foldStore);
     expect(lines).toHaveLength(2);
   });
+
+  it("prefix fold returns cached oldest rows followed by the visible newest rows", () => {
+    const promptLine = lineFromSpec("$ build");
+    const cached1 = lineFromSpec("step 1");
+    const cached2 = lineFromSpec("step 2");
+    const visible3 = lineFromSpec("step 3");
+    const visible4 = lineFromSpec("step 4");
+    const term = fakeTerm([promptLine, visible3, visible4]);
+    const foldStore = {
+      getFold: (id: number) => id === 9
+        ? { kind: "prefix" as const, savedLines: [cached1, cached2] }
+        : undefined,
+    };
+
+    const lines = resolveBlockLines(term as any, fakeBlock(9, 0, null), foldStore);
+
+    expect(lines).toEqual([promptLine, cached1, cached2, visible3, visible4]);
+  });
 });
 
 describe("extractBlocksText with foldStore", () => {

src/lib/terminal/block-content.ts

@@ -19,7 +19,10 @@ import type { CommandBlock } from "./command-blocks";
 /** 折叠仓库的最小接口，只用 getFold 查 saved body。
  *  避免直接 import FoldStore，让本模块对 folds.ts 的依赖只剩"读"语义。 */
 export interface FoldLookup {
-  getFold(blockId: number): { savedLines: unknown[] } | undefined;
+  getFold(blockId: number): {
+    kind?: "full" | "prefix";
+    savedLines: unknown[];
+  } | undefined;
 }
 
 /** 一个块的可视行号范围。end 缺失时 fallback 到 cursor 绝对行（块还在写）。 */
@@ -69,7 +72,16 @@ export function resolveBlockLines(
   if (fold) {
     const prompt = buf.getLine(block.start.line);
     const body = fold.savedLines as unknown as IBufferLine[];
-    return prompt ? [prompt, ...body] : [...body];
+    const out = prompt ? [prompt, ...body] : [...body];
+    if (fold.kind !== "prefix") return out;
+
+    const cursorAbs = buf.baseY + buf.cursorY;
+    const endLine = block.end && !block.end.isDisposed ? block.end.line : cursorAbs;
+    for (let y = block.start.line + 1; y <= endLine; y++) {
+      const line = buf.getLine(y);
+      if (line) out.push(line);
+    }
+    return out;
   }
   const cursorAbs = buf.baseY + buf.cursorY;
   const endLine = block.end && !block.end.isDisposed ? block.end.line : cursorAbs;