feat(HAI-034): use humanized worktree names instead of task-ID-based directories

- Add worktree-names module with adjective-animal name generator (generateWorktreeName)
- Update executor to assign humanized random worktree names and support dependency worktree reuse
- Remove task-ID fallback paths from merger and store; add shared worktree cleanup via findWorktreeUser
- Remove worktree pool module and related scheduler/integration tests
- Update dashboard worktree label tests and add JSDoc documentation for worktree naming

packages/engine/src/worktree-names.ts

@@ -0,0 +1,76 @@
+import { readdirSync } from "node:fs";
+import { join } from "node:path";
+import { existsSync } from "node:fs";
+
+const ADJECTIVES = [
+  "amber", "azure", "bold", "brave", "bright",
+  "calm", "clear", "cool", "coral", "crisp",
+  "deft", "dusky", "eager", "early", "faint",
+  "fast", "fleet", "fresh", "gentle", "gilt",
+  "glad", "grand", "green", "happy", "hazy",
+  "ivory", "jade", "keen", "lemon", "light",
+  "lunar", "maple", "merry", "misty", "noble",
+  "opal", "pale", "pearl", "plush", "proud",
+  "quiet", "rapid", "rosy", "rusty", "sandy",
+  "sharp", "sleek", "solar", "swift", "vivid",
+];
+
+const NOUNS = [
+  "badger", "breeze", "brook", "cedar", "cliff",
+  "crane", "daisy", "delta", "dune", "eagle",
+  "ember", "falcon", "fern", "finch", "flame",
+  "frost", "grove", "hawk", "heron", "iris",
+  "lark", "lotus", "maple", "marsh", "mesa",
+  "moss", "oak", "olive", "orbit", "otter",
+  "panda", "peach", "petal", "pine", "plume",
+  "quail", "raven", "reef", "ridge", "robin",
+  "sage", "shore", "spark", "stone", "swift",
+  "thorn", "tiger", "trail", "trout", "wren",
+];
+
+/**
+ * Generate a random, human-friendly worktree directory name.
+ *
+ * Names follow an `adjective-noun` pattern (e.g., `swirly-monkey`,
+ * `quiet-falcon`, `bright-orchid`) drawn from embedded word lists of
+ * ~50 adjectives × ~50 nouns, producing ~2,500 unique combinations.
+ *
+ * **Collision avoidance:** The function checks existing subdirectories
+ * under `<rootDir>/.worktrees/`. If the randomly chosen name already
+ * exists, a numeric suffix is appended (e.g., `swift-falcon-2`,
+ * `swift-falcon-3`) until a unique name is found.
+ *
+ * @param rootDir - The project root directory (parent of `.worktrees/`)
+ * @returns A unique worktree directory name (not a full path)
+ */
+export function generateWorktreeName(rootDir: string): string {
+  const adjective = ADJECTIVES[Math.floor(Math.random() * ADJECTIVES.length)];
+  const noun = NOUNS[Math.floor(Math.random() * NOUNS.length)];
+  const baseName = `${adjective}-${noun}`;
+
+  const worktreesDir = join(rootDir, ".worktrees");
+  const existing = getExistingWorktreeNames(worktreesDir);
+
+  if (!existing.has(baseName)) {
+    return baseName;
+  }
+
+  // Collision — append numeric suffix
+  let suffix = 2;
+  while (existing.has(`${baseName}-${suffix}`)) {
+    suffix++;
+  }
+  return `${baseName}-${suffix}`;
+}
+
+function getExistingWorktreeNames(worktreesDir: string): Set<string> {
+  if (!existsSync(worktreesDir)) {
+    return new Set();
+  }
+  try {
+    const entries = readdirSync(worktreesDir, { withFileTypes: true });
+    return new Set(entries.filter((e) => e.isDirectory()).map((e) => e.name));
+  } catch {
+    return new Set();
+  }
+}