test: structural regression tests for session memory/CPU leak fixes

Verifies that defensive guards (render-skip, chat cap, dispose, signal
handler cleanup, alert cap, orphan kill) are present in source. These
are structural tests because the leaks manifest over hours of real
usage, not in unit test timescales.

src/tests/session-memory-leaks.test.ts

@@ -0,0 +1,144 @@
+/**
+ * Regression tests for CPU/memory leak fixes in long-running sessions.
+ *
+ * Structural tests that verify the fix patterns are present in source —
+ * NOT runtime integration tests. This approach is chosen because:
+ * - The leaks manifest over hours of real usage, not in unit test timescales
+ * - The fixes are defensive guards (caps, disposal, handler cleanup)
+ * - Structural verification catches regressions when code is refactored
+ */
+import test from "node:test";
+import assert from "node:assert/strict";
+import { readFileSync } from "node:fs";
+import { join } from "node:path";
+
+// ── Helpers ──────────────────────────────────────────────────────────
+
+function readSource(relativePath: string): string {
+  return readFileSync(join(import.meta.dirname, "..", "..", relativePath), "utf-8");
+}
+
+function extractFunctionBody(src: string, name: string): string {
+  const fnStart = src.indexOf(name);
+  assert.ok(fnStart > -1, `${name} must exist in source`);
+  let depth = 0;
+  let fnEnd = -1;
+  for (let i = src.indexOf("{", fnStart); i < src.length; i++) {
+    if (src[i] === "{") depth++;
+    if (src[i] === "}") depth--;
+    if (depth === 0) { fnEnd = i; break; }
+  }
+  return src.slice(fnStart, fnEnd + 1);
+}
+
+// ── TUI render-skip ─────────────────────────────────────────────────
+
+test("Container caches render output for stable-reference comparison", () => {
+  const src = readSource("packages/pi-tui/src/tui.ts");
+  assert.ok(
+    src.includes("_prevRender"),
+    "Container must have _prevRender cache for render-skip optimization",
+  );
+});
+
+test("TUI skips post-processing when component output is unchanged", () => {
+  const src = readSource("packages/pi-tui/src/tui.ts");
+  assert.ok(
+    src.includes("_lastRenderedComponents"),
+    "TUI must track _lastRenderedComponents for reference-equality skip",
+  );
+});
+
+// ── Loader frame isolation ──────────────────────────────────────────
+
+test("Loader does not call setText on every spinner tick", () => {
+  const src = readSource("packages/pi-tui/src/components/loader.ts");
+  // The old pattern was: setText(`${frame} ${message}`) inside the interval
+  // The new pattern: only update Text when message changes, prepend frame in render()
+  assert.ok(
+    src.includes("_lastMessage"),
+    "Loader must track _lastMessage to avoid setText on every tick",
+  );
+  // Verify the interval does NOT call setText or updateDisplay
+  const intervalMatch = src.match(/setInterval\s*\(\s*\(\)\s*=>\s*\{([^}]+)\}/s);
+  assert.ok(intervalMatch, "Loader must have a setInterval callback");
+  const intervalBody = intervalMatch[1];
+  assert.ok(
+    !intervalBody.includes("setText") && !intervalBody.includes("updateDisplay"),
+    "Loader interval must NOT call setText or updateDisplay — " +
+    "frame rotation should only trigger requestRender()",
+  );
+});
+
+// ── Text cache guard ────────────────────────────────────────────────
+
+test("Text.setText returns early when text is unchanged", () => {
+  const src = readSource("packages/pi-tui/src/components/text.ts");
+  const setTextBody = extractFunctionBody(src, "setText(");
+  assert.ok(
+    setTextBody.includes("if (this.text === text) return"),
+    "setText must early-return when text is identical to prevent cache invalidation",
+  );
+});
+
+// ── Chat component cap ──────────────────────────────────────────────
+
+test("InteractiveMode caps rendered chat components", () => {
+  const src = readSource("packages/pi-coding-agent/src/modes/interactive/interactive-mode.ts");
+  assert.ok(
+    src.includes("MAX_CHAT_COMPONENTS"),
+    "InteractiveMode must define MAX_CHAT_COMPONENTS to prevent unbounded growth",
+  );
+  assert.ok(
+    src.includes("trimChatHistory"),
+    "InteractiveMode must call trimChatHistory to enforce the cap",
+  );
+});
+
+// ── ToolExecution dispose ───────────────────────────────────────────
+
+test("ToolExecutionComponent has dispose() to clear heavy references", () => {
+  const src = readSource("packages/pi-coding-agent/src/modes/interactive/components/tool-execution.ts");
+  assert.ok(
+    src.includes("dispose()"),
+    "ToolExecutionComponent must have dispose() for GC of image maps, diff previews, etc.",
+  );
+});
+
+// ── Orphan process prevention ───────────────────────────────────────
+
+test("InteractiveMode kills descendant processes on shutdown", () => {
+  const src = readSource("packages/pi-coding-agent/src/modes/interactive/interactive-mode.ts");
+  assert.ok(
+    src.includes("listDescendants"),
+    "Shutdown must use listDescendants to find orphan child processes",
+  );
+  assert.ok(
+    src.includes("SIGTERM") && src.includes("SIGKILL"),
+    "Shutdown must send SIGTERM then SIGKILL to descendants",
+  );
+});
+
+// ── Signal handler accumulation ─────────────────────────────────────
+
+test("bg-shell removes signal handlers on session_shutdown", () => {
+  const src = readSource("src/resources/extensions/bg-shell/bg-shell-lifecycle.ts");
+  assert.ok(
+    src.includes('process.off("SIGTERM"') || src.includes("process.off('SIGTERM'"),
+    "session_shutdown must remove SIGTERM handler to prevent accumulation",
+  );
+  assert.ok(
+    src.includes('process.off("SIGINT"') || src.includes("process.off('SIGINT'"),
+    "session_shutdown must remove SIGINT handler to prevent accumulation",
+  );
+});
+
+// ── Alert queue cap ─────────────────────────────────────────────────
+
+test("pendingAlerts has a maximum size cap", () => {
+  const src = readSource("src/resources/extensions/bg-shell/process-manager.ts");
+  assert.ok(
+    src.includes("MAX_PENDING_ALERTS"),
+    "process-manager must cap pendingAlerts to prevent unbounded growth",
+  );
+});