fix: report unavailable LSP servers explicitly

Evicting the entire entry on derived watcher events was overly aggressive.
Instead, clear cached diagnostics and send a reloadProjects command to the
TypeScript language server so it picks up workspace changes without losing
state.

AGENTS.md

@@ -41,6 +41,40 @@ The daemon tracks opened files per-entry in a `Map<uri, mtimeMs>`. On each reque
 
 A per-entry `serializer` promise chain prevents concurrent syncs from racing.
 
+### Workspace File Watching
+
+Each `ClientEntry` lazily owns a `WorkspaceWatcher` (`src/watcher.ts`,
+chokidar + picomatch) that translates filesystem events into
+`workspace/didChangeWatchedFiles` notifications. This keeps the server's
+workspace index fresh when files are created/changed/deleted **outside** of
+LSP tool calls (build scripts, codegen, `git checkout`, the agent's own
+file writes).
+
+Non-obvious bits:
+
+- **Patterns come from the server.** We honor `client/registerCapability`
+  for `workspace/didChangeWatchedFiles` and store the registrations on the
+  `LspClient`. **Don't re-stub those handlers**; they look harmless but
+  break the entire feature. If a server doesn't register, we don't watch.
+- **Servers send mixed pattern forms.** Gopls registers absolute-path
+  globs (`/abs/root/**/*.go`); others send relative (`**/*.ts`) or
+  `RelativePattern` objects. `compileWatchers()` tries both relative and
+  absolute matching against each event so we accept all forms.
+- **Ignore layering.** Always-ignore baseline (`.git/`, `.DS_Store`) +
+  root `.gitignore` parsed via the `ignore` package + a small fallback
+  for non-git workspaces. Nested gitignores aren't supported yet.
+- **Startup readiness.** The daemon waits for chokidar's initial scan, capped
+  at 5s, so first requests don't hang indefinitely on huge workspaces.
+- **Debounce.** 50ms quiet period, capped at 500ms max wait so sustained
+  event streams (branch switches) still flush in bounded time.
+- **Watcher and mtime-sync coexist.** When the agent edits a file we'll
+  emit `didChangeWatchedFiles` *and* the next request's `syncFile` will
+  send a `didChange`. Servers treat the two as orthogonal (workspace
+  index vs. editor buffer) and dedupe internally. This matches VS Code.
+- **Rollback.** `PI_LSP_DISABLE_WATCHERS=1` short-circuits all watcher
+  creation — if something goes wrong in a real workspace, this restores
+  the prior "only the queried file is synced" behavior.
+
 ### Extension vs Daemon Responsibilities
 
 | Concern | Where |
@@ -55,22 +89,43 @@ A per-entry `serializer` promise chain prevents concurrent syncs from racing.
 
 ```
 index.ts            — Extension entry point (tools, commands, auto-check flag)
-server.ts           — LSP server registry (gopls, typescript-language-server, pyright)
+server.ts           — Built-in LSP server registry (gopls, typescript-language-server, pyright, ...)
 cli.ts              — CLI for testing/debugging (daemon-aware or --no-daemon)
 daemon.ts           — Entrypoint that starts the daemon process
 
 src/
-  client.ts         — LspClient: spawns a language server, JSON-RPC handshake, file sync
+  client.ts         — LspClient: spawns a language server, JSON-RPC handshake, file sync, file-watcher registrations
+  watcher.ts        — WorkspaceWatcher: chokidar + picomatch → workspace/didChangeWatchedFiles batches
   commands.ts       — CLI command dispatcher (maps command names → LSP methods)
+  config.ts         — Per-repo `.pi-lsp.json` loader: walk-up + merge with built-ins, mtime cache
   daemonClient.ts   — High-level helpers (daemonRequest, daemonDiagnostics, etc.)
   daemonProtocol.ts — Shared types, socket path, NDJSON send/receive, autospawn logic
-  root.ts           — pickServer(), findRoot(), URI/path conversion
+  root.ts           — pickServer(), findServerById(), getServersForPath(), findRoot(), URI/path conversion
   types.ts          — ServerConfig interface, LspCommand union
 ```
 
-## Adding a Server
+### Per-Repo Config (`.pi-lsp.json`)
 
-Edit `server.ts`. Add an entry to the `servers` array:
+Users can add/override/disable servers without editing `server.ts`. `src/config.ts`
+walks upward from a given path to find `.pi-lsp.json`, parses it, and merges
+with the built-in `servers` list:
+
+- New `id` → appended (must supply `match`, `command`, `args`, `rootMarkers`).
+- Existing `id` → shallow-merged over the built-in (user fields win).
+- `disable: []` → filtered out at the end.
+
+Results are cached per config path, invalidated by mtime. `getServersForPath(p)`
+is the **single entry point** — don't import the raw `servers` array from
+`server.ts` outside `src/config.ts`. The daemon resolves servers at
+`getOrCreateEntry()` time via `findServerById(filePath, id)`, so spawned
+servers reflect the config of the file being acted on. **Already-running**
+entries don't see config changes; users must `/lsp-destroy` to respawn.
+
+## Adding a Server (Built-In)
+
+For servers shipped with pi-lsp, edit `server.ts`. (For per-repo additions,
+users should drop a `.pi-lsp.json` at the repo root — see README.) Add an entry
+to the `servers` array:
 
 ```typescript
 {

README.md

@@ -123,6 +123,44 @@ Edit `server.ts`:
 }
 ```
 
+## Per-Repo Config (`.pi-lsp.json`)
+
+Drop a `.pi-lsp.json` at any ancestor of your working files to add or override
+servers for that repo. The nearest config (walking upward) wins.
+
+```json
+{
+  "servers": [
+    {
+      "id": "rust-analyzer",
+      "match": ["rs"],
+      "command": "rust-analyzer",
+      "args": [],
+      "rootMarkers": ["Cargo.toml"],
+      "languageId": "rust"
+    },
+    { "id": "gopls", "args": ["-remote=auto", "-vv"] }
+  ],
+  "disable": ["oxlint"]
+}
+```
+
+**Merge rules:**
+
+- Entry with a built-in `id` → fields shallow-merge over the built-in (user wins).
+- Entry with a new `id` → appended; must include `match`, `command`, `args`, `rootMarkers`.
+- `disable` → filters out matching ids (built-in or user-defined).
+
+**Reloading after edits:** Config is re-read on mtime change, so new lookups
+pick up changes automatically. However, **already-running** language servers in
+the daemon keep their original spawn args. If you change `command`, `args`, or
+`rootMarkers`, run `/lsp-destroy` (or `pi-lsp daemon stop`) so they respawn
+with the new config.
+
+**Security note:** `.pi-lsp.json` controls what binary pi-lsp spawns. Treat it
+like `.vscode/settings.json` — don't accept untrusted configs from arbitrary
+repos.
+
 ## Adding A Command
 
 1. Add to the `LspCommand` union in `src/types.ts`.

cli.ts

@@ -2,7 +2,7 @@
 import * as path from "node:path";
 import { startClientForFile } from "./src/client.ts";
 import { isLspCommand, listCommands, runCommand } from "./src/commands.ts";
-import { pickServer } from "./src/root.ts";
+import { pickServer, isServerAvailable, getServersForPath } from "./src/root.ts";
 import {
   daemonDiagnostics,
   daemonRequest,
@@ -104,14 +104,21 @@ async function runViaDaemon(
   const filePath = path.resolve(fileArg);
   let result: unknown;
   if (cmdArg === "diagnostics") {
-    result = await daemonDiagnostics(filePath);
+    // Pick All Available Servers For Diagnostics - Resolves against any
+    // `.pi-lsp.json` reachable from the file so per-repo overrides apply.
+    const ext = path.extname(filePath).replace(/^\./, "");
+    const serverIds = getServersForPath(filePath)
+      .filter((s) => s.match.includes(ext) && isServerAvailable(s))
+      .map((s) => s.id);
+    result = await daemonDiagnostics(filePath, serverIds);
   } else if (cmdArg in methodMap) {
+    const server = pickServer(filePath);
     // References Default - Match commands.ts: include declaration unless
     // caller explicitly overrode `context`.
     if (cmdArg === "references" && !("context" in params)) {
       params.context = { includeDeclaration: true };
     }
-    result = await daemonRequest(filePath, methodMap[cmdArg], params);
+    result = await daemonRequest(filePath, server.id, methodMap[cmdArg], params);
   } else {
     process.stderr.write(
       `Unknown command "${cmdArg}". Known: ${listCommands().join(", ")}\n`,

flake.nix

@@ -20,8 +20,14 @@
       {
         devShells.default = pkgs.mkShell {
           packages = with pkgs; [
+            oxlint
             nodejs_22
             typescript-language-server
+
+            # Tests
+            go
+            gopls
+            pyright
           ];
         };
       }

index.ts

@@ -12,15 +12,34 @@ import {
   daemonRequest,
   daemonStatus,
 } from "./src/daemonClient.ts";
-import { pickServer } from "./src/root.ts";
-import { servers } from "./server.ts";
+import { pickServer, isServerAvailable, getServersForPath } from "./src/root.ts";
 import {
   ServerNotFoundError,
   UnsupportedExtensionError,
 } from "./src/types.ts";
 
+type LspUnavailable = { piLspUnavailable: true; message: string };
+
+function lspUnavailable(message: string): LspUnavailable {
+  return { piLspUnavailable: true, message };
+}
+
+function isLspUnavailable(result: unknown): result is LspUnavailable {
+  return Boolean(
+    result &&
+      typeof result === "object" &&
+      "piLspUnavailable" in result &&
+      (result as { piLspUnavailable?: unknown }).piLspUnavailable === true,
+  );
+}
+
+function formatUnavailable(result: LspUnavailable): string {
+  return `(LSP unavailable: ${result.message})`;
+}
+
 // Format Hover - Turn an LSP hover response into readable text.
 function formatHover(result: unknown): string {
+  if (isLspUnavailable(result)) return formatUnavailable(result);
   if (!result || typeof result !== "object") return "(no hover info)";
   const hover = result as { contents?: unknown };
   if (!hover.contents) return "(empty)";
@@ -50,6 +69,7 @@ function formatHover(result: unknown): string {
 
 // Format Definition - Turn definition locations into readable text.
 function formatDefinition(result: unknown): string {
+  if (isLspUnavailable(result)) return formatUnavailable(result);
   if (!result) return "(no definition found)";
   const locations = Array.isArray(result) ? result : [result];
   if (locations.length === 0) return "(no definition found)";
@@ -65,6 +85,7 @@ function formatDefinition(result: unknown): string {
 
 // Format References - Turn reference locations into readable text.
 function formatReferences(result: unknown): string {
+  if (isLspUnavailable(result)) return formatUnavailable(result);
   if (!result || !Array.isArray(result)) return "(no references found)";
   if (result.length === 0) return "(no references found)";
 
@@ -86,6 +107,7 @@ function formatReferences(result: unknown): string {
 
 // Format Completions - Turn completion items into readable text.
 function formatCompletions(result: unknown): string {
+  if (isLspUnavailable(result)) return formatUnavailable(result);
   if (!result) return "(no completions)";
 
   // Resolve to CompletionItem[] if it's a CompletionList
@@ -151,6 +173,7 @@ function formatCompletions(result: unknown): string {
 
 // Format Document Symbols - Turn symbols into a tree outline.
 function formatDocumentSymbols(result: unknown): string {
+  if (isLspUnavailable(result)) return formatUnavailable(result);
   if (!result || !Array.isArray(result)) return "(no symbols)";
   const symbols = result as any[];
   if (symbols.length === 0) return "(no symbols)";
@@ -201,17 +224,8 @@ function formatDocumentSymbols(result: unknown): string {
 }
 
 // Format Diagnostics - Turn diagnostic messages into readable text.
-function formatDiagnostics(result: unknown, limit = 20): string {
-  if (
-    !result ||
-    typeof result !== "object" ||
-    !("diagnostics" in result)
-  ) {
-    return "(no diagnostics)";
-  }
-  const diags = (result as any).diagnostics;
-  if (!Array.isArray(diags) || diags.length === 0) return "(no diagnostics)";
-
+// Format Single Server Diagnostics - Renders one server's diagnostics list.
+function formatServerDiagnostics(diags: any[], limit: number): string {
   const severityNames: Record<number, string> = {
     1: "Error",
     2: "Warning",
@@ -236,11 +250,46 @@ function formatDiagnostics(result: unknown, limit = 20): string {
     .join("\n");
 
   if (diags.length > limit) {
-    return `${formatted}\n\n... and ${diags.length - limit} more diagnostics (showing first ${limit})`;
+    return `${formatted}\n\n... and ${diags.length - limit} more (showing first ${limit})`;
   }
   return formatted;
 }
 
+// Format Diagnostics - Handles the grouped result map from the daemon:
+// { [serverId]: { uri, diagnostics[] } }. Single-server results omit the
+// header to avoid noise.
+function formatDiagnostics(result: unknown, limit = 20): string {
+  if (isLspUnavailable(result)) return formatUnavailable(result);
+  if (!result || typeof result !== "object") return "(no diagnostics)";
+
+  const grouped = result as Record<string, any>;
+  const serverIds = Object.keys(grouped);
+  if (serverIds.length === 0) return "(no diagnostics)";
+
+  // Collect Servers With Diagnostics
+  const sections: { id: string; diags: any[] }[] = [];
+  for (const id of serverIds) {
+    const entry = grouped[id];
+    const diags = entry?.diagnostics;
+    if (Array.isArray(diags) && diags.length > 0) {
+      sections.push({ id, diags });
+    }
+  }
+
+  if (sections.length === 0) return "(no diagnostics)";
+
+  // Single Server - Skip header for brevity.
+  if (sections.length === 1) {
+    return formatServerDiagnostics(sections[0].diags, limit);
+  }
+
+  // Multiple Servers - Group with headers.
+  const perServer = Math.max(5, Math.floor(limit / sections.length));
+  return sections
+    .map((s) => `## ${s.id}\n${formatServerDiagnostics(s.diags, perServer)}`)
+    .join("\n\n");
+}
+
 // Is Expected Error - Returns true if the error is an expected condition
 // (unsupported file type or missing server binary) that should be
 // suppressed rather than surfaced to the user.
@@ -251,6 +300,34 @@ function isExpectedError(error: unknown): boolean {
   );
 }
 
+function unavailableForFile(filePath: string, includeDiagnosticsOnly = false): LspUnavailable {
+  const ext = path.extname(filePath).replace(/^\./, "");
+  const label = ext ? `.${ext}` : "files without an extension";
+  const matches = getServersForPath(filePath).filter((server) =>
+    server.match.includes(ext) && (includeDiagnosticsOnly || !server.diagnosticsOnly)
+  );
+
+  if (matches.length === 0) {
+    return lspUnavailable(`no LSP server is registered for ${label}`);
+  }
+
+  const disabled = matches.filter((server) => disabledServers.has(server.id));
+  if (disabled.length === matches.length) {
+    return lspUnavailable(
+      `matching LSP server(s) are disabled: ${disabled.map((s) => s.id).join(", ")}`,
+    );
+  }
+
+  const unavailable = matches.filter((server) => !isServerAvailable(server));
+  if (unavailable.length > 0) {
+    return lspUnavailable(
+      `matching LSP server(s) are not on PATH: ${unavailable.map((s) => s.command).join(", ")}`,
+    );
+  }
+
+  return lspUnavailable(`no applicable LSP server is available for ${label}`);
+}
+
 // Disabled Servers - In-memory set of disabled server IDs. Scoped to this
 // extension process; the shared daemon is never mutated by disable/enable.
 const lspToolNames = [
@@ -277,14 +354,12 @@ async function runLsp(
     // touching the daemon so other pi instances sharing it are unaffected.
     const server = pickServer(filePath);
     if (disabledServers.has(server.id)) {
-      throw new Error(
-        `LSP server "${server.id}" is disabled. Use /lsp-enable ${server.id} to re-enable.`,
-      );
+      return unavailableForFile(filePath);
     }
-    return await daemonRequest(filePath, method, params);
+    return await daemonRequest(filePath, server.id, method, params);
   } catch (error) {
     if (isExpectedError(error)) {
-      return undefined;
+      return unavailableForFile(filePath);
     }
     // Daemon-wrapped errors (plain Error with expected message) are also
     // expected — the daemon catches pickServer() throws and returns them
@@ -294,31 +369,51 @@ async function runLsp(
       (error.message.includes("No LSP server registered") ||
         error.message.includes("not found on PATH"))
     ) {
-      return undefined;
+      return unavailableForFile(filePath);
     }
     throw error;
   }
 }
 
-// Run LSP Diagnostics - Diagnostics arrive as a notification, so the
-// daemon has a dedicated op that waits for the next publish. Expected
-// errors (unsupported file type, missing binary) are suppressed.
+// Pick Diagnostic Servers - Returns all available, non-disabled servers
+// matching the file's extension. Resolves the per-repo config from the
+// file's directory so user-defined servers participate in fan-out.
+function pickDiagnosticServers(filePath: string): string[] {
+  const ext = path.extname(filePath).replace(/^\./, "");
+  return getServersForPath(filePath)
+    .filter((s) => s.match.includes(ext) && isServerAvailable(s) && !disabledServers.has(s.id))
+    .map((s) => s.id);
+}
+
+// Timeout Wrapper - Rejects a promise after the given number of milliseconds.
+// Used to prevent async hooks from blocking pi indefinitely.
+function withTimeout<T>(promise: Promise<T>, ms: number): Promise<T> {
+  return new Promise((resolve, reject) => {
+    const timer = setTimeout(() => reject(new Error(`Timeout after ${ms}ms`)), ms);
+    promise.then(
+      (value) => { clearTimeout(timer); resolve(value); },
+      (reason) => { clearTimeout(timer); reject(reason); },
+    );
+  });
+}
+
+// Run LSP Diagnostics - Fans out to all matching servers in a single
+// daemon call. Returns an explicit unavailable result if no server applies.
 async function runDiagnostics(filePath: string): Promise<unknown> {
   try {
-    return await daemonDiagnostics(filePath, 1500);
+    const serverIds = pickDiagnosticServers(filePath);
+    if (serverIds.length === 0) return unavailableForFile(filePath, true);
+    return await daemonDiagnostics(filePath, serverIds, 1500);
   } catch (error) {
     if (isExpectedError(error)) {
-      return undefined;
+      return unavailableForFile(filePath, true);
     }
-    // Daemon-wrapped errors (plain Error with expected message) are also
-    // expected — the daemon catches pickServer() throws and returns them
-    // as string error messages.
     if (
       error instanceof Error &&
       (error.message.includes("No LSP server registered") ||
         error.message.includes("not found on PATH"))
     ) {
-      return undefined;
+      return unavailableForFile(filePath, true);
     }
     throw error;
   }
@@ -492,9 +587,12 @@ export default function (pi: ExtensionAPI) {
 
     try {
       const absolutePath = path.resolve(ctx.cwd, filePath);
-      // daemonDiagnostics triggers getOrCreateEntry + syncFile in the daemon.
-      // We don't await it — just fire and forget so the server starts warming up.
-      void daemonDiagnostics(absolutePath).catch(() => {});
+      // Warm Diagnostic Servers - Fire-and-forget so servers are ready by
+      // the time an LSP tool is called.
+      const serverIds = pickDiagnosticServers(absolutePath);
+      if (serverIds.length > 0) {
+        void daemonDiagnostics(absolutePath, serverIds).catch(() => {});
+      }
     } catch {
       // Silently ignore — unsupported file type, missing binary, etc.
     }
@@ -506,7 +604,9 @@ export default function (pi: ExtensionAPI) {
     if (!pi.getFlag("lsp-auto-check")) return;
 
     // Skip If All Disabled - No LSP server is available for this instance.
-    if (servers.every((s) => disabledServers.has(s.id))) return;
+    // Resolve against ctx.cwd so user-defined servers count toward this check.
+    const cwdServers = getServersForPath(ctx.cwd);
+    if (cwdServers.every((s) => disabledServers.has(s.id))) return;
 
     // Edit & Write Only
     if (!["edit", "write"].includes(event.toolName)) return;
@@ -520,8 +620,10 @@ export default function (pi: ExtensionAPI) {
     const absolutePath = path.resolve(ctx.cwd, filePath);
 
     try {
-      // Run LSP diagnostics
-      const result = await runDiagnostics(absolutePath);
+      // Run LSP diagnostics with timeout - Prevent the auto-check hook from
+      // blocking pi if the daemon or LSP server is slow or unresponsive.
+      const result = await withTimeout(runDiagnostics(absolutePath), 3000);
+      if (isLspUnavailable(result)) return;
       const formatted = formatDiagnostics(result, 10);
 
       // Only send a message if there are actual diagnostics
@@ -584,9 +686,16 @@ export default function (pi: ExtensionAPI) {
 
   // --- Server Control Commands ---
 
+  // Resolve Active Servers - Per-cwd helper so commands see the same
+  // per-repo overrides the LLM does. We accept an optional cwd because some
+  // closures (e.g. completions) don't get a context.
+  const resolveServers = (cwd?: string) => getServersForPath(cwd ?? process.cwd());
+
   // Shared Argument Completions - Suggests registered server IDs plus "all".
+  // Uses process.cwd() since completion handlers don't receive a context;
+  // close enough for argument hints.
   const serverCompletions = (prefix: string) => {
-    const ids = [...servers.map((s) => s.id), "all"].filter((id) =>
+    const ids = [...resolveServers().map((s) => s.id), "all"].filter((id) =>
       id.startsWith(prefix),
     );
     return ids.length > 0 ? ids.map((id) => ({ value: id, label: id })) : null;
@@ -594,16 +703,17 @@ export default function (pi: ExtensionAPI) {
 
   // Parse Server IDs - Validates args against registered servers. Bare/empty
   // or "all" returns every server ID. Throws on unknown names.
-  function parseServerIds(args: string | undefined): string[] {
-    if (!args || !args.trim()) return servers.map((s) => s.id);
+  function parseServerIds(args: string | undefined, cwd: string): string[] {
+    const list = resolveServers(cwd);
+    if (!args || !args.trim()) return list.map((s) => s.id);
     const ids = args.trim().split(/\s+/);
-    if (ids.includes("all")) return servers.map((s) => s.id);
-    const invalid = ids.filter((id) => !servers.some((s) => s.id === id));
+    if (ids.includes("all")) return list.map((s) => s.id);
+    const invalid = ids.filter((id) => !list.some((s) => s.id === id));
     if (invalid.length > 0) {
       throw new Error(
         `Unknown server(s): ${invalid.join(
           ", ",
-        )}. Available: ${servers.map((s) => s.id).join(", ")}`,
+        )}. Available: ${list.map((s) => s.id).join(", ")}`,
       );
     }
     return ids;
@@ -612,9 +722,10 @@ export default function (pi: ExtensionAPI) {
   // Update Tool Visibility - When all servers are disabled, remove LSP tools
   // from the active set so the LLM won't attempt them. When any is enabled,
   // restore them. Captures current active tools at toggle time.
-  function updateToolVisibility(): void {
+  function updateToolVisibility(cwd: string): void {
+    const list = resolveServers(cwd);
     const current = pi.getActiveTools();
-    if (servers.every((s) => disabledServers.has(s.id))) {
+    if (list.every((s) => disabledServers.has(s.id))) {
       // All disabled — strip LSP tools
       pi.setActiveTools(current.filter((name) => !lspToolNames.includes(name)));
     } else {
@@ -664,13 +775,13 @@ export default function (pi: ExtensionAPI) {
     getArgumentCompletions: serverCompletions,
     handler: async (args, ctx) => {
       try {
-        const ids = parseServerIds(args);
+        const ids = parseServerIds(args, ctx.cwd);
         for (const id of ids) {
           disabledServers.add(id);
         }
-        updateToolVisibility();
-        const label =
-          ids.length === servers.length ? "all servers" : ids.join(", ");
+        updateToolVisibility(ctx.cwd);
+        const total = resolveServers(ctx.cwd).length;
+        const label = ids.length === total ? "all servers" : ids.join(", ");
         ctx.ui.notify(`Disabled: ${label}`, "info");
       } catch (error) {
         const msg =
@@ -690,13 +801,13 @@ export default function (pi: ExtensionAPI) {
     getArgumentCompletions: serverCompletions,
     handler: async (args, ctx) => {
       try {
-        const ids = parseServerIds(args);
+        const ids = parseServerIds(args, ctx.cwd);
         for (const id of ids) {
           disabledServers.delete(id);
         }
-        updateToolVisibility();
-        const label =
-          ids.length === servers.length ? "all servers" : ids.join(", ");
+        updateToolVisibility(ctx.cwd);
+        const total = resolveServers(ctx.cwd).length;
+        const label = ids.length === total ? "all servers" : ids.join(", ");
         ctx.ui.notify(`Enabled: ${label}`, "info");
       } catch (error) {
         const msg =
@@ -716,16 +827,16 @@ export default function (pi: ExtensionAPI) {
     getArgumentCompletions: serverCompletions,
     handler: async (args, ctx) => {
       try {
-        const ids = parseServerIds(args);
-        if (ids.length === servers.length) {
+        const ids = parseServerIds(args, ctx.cwd);
+        const total = resolveServers(ctx.cwd).length;
+        if (ids.length === total) {
           await daemonDestroyServer();
         } else {
           for (const id of ids) {
             await daemonDestroyServer(id);
           }
         }
-        const label =
-          ids.length === servers.length ? "all servers" : ids.join(", ");
+        const label = ids.length === total ? "all servers" : ids.join(", ");
         ctx.ui.notify(`Destroyed: ${label}`, "info");
       } catch (error) {
         const msg =

package-lock.json

@@ -8,6 +8,9 @@
       "name": "@evan/pi-lsp",
       "version": "0.1.0",
       "dependencies": {
+        "chokidar": "^5.0.0",
+        "ignore": "^7.0.5",
+        "picomatch": "^4.0.4",
         "vscode-jsonrpc": "^8.2.1",
         "vscode-languageserver-protocol": "^3.17.5"
       },
@@ -17,6 +20,7 @@
       "devDependencies": {
         "@mariozechner/pi-coding-agent": "^0.72.0",
         "@types/node": "^22.10.0",
+        "@types/picomatch": "^4.0.3",
         "oxlint": "^1.62.0",
         "tsx": "^4.19.2",
         "typebox": "^1.1.37",
@@ -2789,6 +2793,13 @@
         "undici-types": "~6.21.0"
       }
     },
+    "node_modules/@types/picomatch": {
+      "version": "4.0.3",
+      "resolved": "https://registry.npmjs.org/@types/picomatch/-/picomatch-4.0.3.tgz",
+      "integrity": "sha512-iG0T6+nYJ9FAPmx9SsUlnwcq1ZVRuCXcVEvWnntoPlrOpwtSTKNDC9uVAxTsC3PUvJ+99n4RpAcNgBbHX3JSnQ==",
+      "dev": true,
+      "license": "MIT"
+    },
     "node_modules/@types/retry": {
       "version": "0.12.0",
       "resolved": "https://registry.npmjs.org/@types/retry/-/retry-0.12.0.tgz",
@@ -2967,6 +2978,21 @@
         "url": "https://github.com/chalk/chalk?sponsor=1"
       }
     },
+    "node_modules/chokidar": {
+      "version": "5.0.0",
+      "resolved": "https://registry.npmjs.org/chokidar/-/chokidar-5.0.0.tgz",
+      "integrity": "sha512-TQMmc3w+5AxjpL8iIiwebF73dRDF4fBIieAqGn9RGCWaEVwQ6Fb2cGe31Yns0RRIzii5goJ1Y7xbMwo1TxMplw==",
+      "license": "MIT",
+      "dependencies": {
+        "readdirp": "^5.0.0"
+      },
+      "engines": {
+        "node": ">= 20.19.0"
+      },
+      "funding": {
+        "url": "https://paulmillr.com/funding/"
+      }
+    },
     "node_modules/cli-highlight": {
       "version": "2.1.11",
       "resolved": "https://registry.npmjs.org/cli-highlight/-/cli-highlight-2.1.11.tgz",
@@ -3642,7 +3668,6 @@
       "version": "7.0.5",
       "resolved": "https://registry.npmjs.org/ignore/-/ignore-7.0.5.tgz",
       "integrity": "sha512-Hs59xBNfUIunMFgWAbGX5cq6893IbWg4KnrjbYwX3tx0ztorVgTDA6B2sxf8ejHJ4wz8BqGUMYlnzNBer5NvGg==",
-      "dev": true,
       "license": "MIT",
       "engines": {
         "node": ">= 4"
@@ -4085,6 +4110,18 @@
       "dev": true,
       "license": "MIT"
     },
+    "node_modules/picomatch": {
+      "version": "4.0.4",
+      "resolved": "https://registry.npmjs.org/picomatch/-/picomatch-4.0.4.tgz",
+      "integrity": "sha512-QP88BAKvMam/3NxH6vj2o21R6MjxZUAd6nlwAS/pnGvN9IVLocLHxGYIzFhg6fUQ+5th6P4dv4eW9jX3DSIj7A==",
+      "license": "MIT",
+      "engines": {
+        "node": ">=12"
+      },
+      "funding": {
+        "url": "https://github.com/sponsors/jonschlinkert"
+      }
+    },
     "node_modules/proper-lockfile": {
       "version": "4.1.2",
       "resolved": "https://registry.npmjs.org/proper-lockfile/-/proper-lockfile-4.1.2.tgz",
@@ -4180,6 +4217,19 @@
         "once": "^1.3.1"
       }
     },
+    "node_modules/readdirp": {
+      "version": "5.0.0",
+      "resolved": "https://registry.npmjs.org/readdirp/-/readdirp-5.0.0.tgz",
+      "integrity": "sha512-9u/XQ1pvrQtYyMpZe7DXKv2p5CNvyVwzUB6uhLAnQwHMSgKMBR62lc7AHljaeteeHXn11XTAaLLUVZYVZyuRBQ==",
+      "license": "MIT",
+      "engines": {
+        "node": ">= 20.19.0"
+      },
+      "funding": {
+        "type": "individual",
+        "url": "https://paulmillr.com/funding/"
+      }
+    },
     "node_modules/require-directory": {
       "version": "2.1.1",
       "resolved": "https://registry.npmjs.org/require-directory/-/require-directory-2.1.1.tgz",

package.json

@@ -21,12 +21,16 @@
     "test:integration": "NODE_OPTIONS='--import=tsx' node --test test/integration/**/*.ts"
   },
   "dependencies": {
+    "chokidar": "^5.0.0",
+    "ignore": "^7.0.5",
+    "picomatch": "^4.0.4",
     "vscode-jsonrpc": "^8.2.1",
     "vscode-languageserver-protocol": "^3.17.5"
   },
   "devDependencies": {
     "@mariozechner/pi-coding-agent": "^0.72.0",
     "@types/node": "^22.10.0",
+    "@types/picomatch": "^4.0.3",
     "oxlint": "^1.62.0",
     "tsx": "^4.19.2",
     "typebox": "^1.1.37",

server.ts

@@ -3,8 +3,42 @@
 //
 // Add new servers here. `match` is a list of file extensions (no dot) OR
 // language ids; either matches.
+import * as fs from "node:fs";
+import * as path from "node:path";
 import type { ServerConfig } from "./src/types.ts";
 
+// Resolve Python Path - Prefer the project's virtualenv when present so
+// Pyright sees the same interpreter/dependencies as project commands.
+function resolvePythonPath(rootDir: string): string | undefined {
+  const candidates = [
+    path.join(rootDir, ".venv", "bin", "python"),
+    path.join(rootDir, "venv", "bin", "python"),
+  ];
+  return candidates.find((candidate) => fs.existsSync(candidate));
+}
+
+// Pyright Settings - Minimal editor settings needed for diagnostics and import
+// resolution. Shared by workspace/configuration and didChangeConfiguration.
+function pyrightSettings(rootDir: string): {
+  pythonPath: string | undefined;
+  analysis: {
+    diagnosticMode: string;
+    typeCheckingMode: string;
+    autoSearchPaths: boolean;
+    useLibraryCodeForTypes: boolean;
+  };
+} {
+  return {
+    pythonPath: resolvePythonPath(rootDir),
+    analysis: {
+      diagnosticMode: "openFilesOnly",
+      typeCheckingMode: "basic",
+      autoSearchPaths: true,
+      useLibraryCodeForTypes: true,
+    },
+  };
+}
+
 // Global Root Markers — appended to every server's rootMarkers list
 export const globalRootMarkers = [".git"];
 
@@ -25,6 +59,20 @@ export const servers: ServerConfig[] = [
     rootMarkers: ["pnpm-workspace.yaml", "tsconfig.json", "package.json"],
     languageId: "typescript",
   },
+  {
+    id: "svelteserver",
+    match: ["svelte"],
+    command: "svelteserver",
+    args: ["--stdio"],
+    rootMarkers: [
+      "svelte.config.js",
+      "svelte.config.ts",
+      "svelte.config.cjs",
+      "svelte.config.mjs",
+      "package.json",
+    ],
+    languageId: "svelte",
+  },
   {
     id: "pyright",
     match: ["py"],
@@ -32,6 +80,15 @@ export const servers: ServerConfig[] = [
     args: ["--stdio"],
     rootMarkers: ["pyproject.toml", "setup.py", "setup.cfg"],
     languageId: "python",
+    workspaceConfiguration: {
+      initialSettings: ({ rootDir }) => ({ python: pyrightSettings(rootDir) }),
+      getSection: (section, { rootDir }) => {
+        const settings = pyrightSettings(rootDir);
+        if (section === "python") return settings;
+        if (section === "python.analysis") return settings.analysis;
+        return null;
+      },
+    },
   },
   {
     id: "lua-language-server",
@@ -43,12 +100,44 @@ export const servers: ServerConfig[] = [
   },
   {
     id: "vscode-html-language-server",
-    match: ["html", "css", "jsonl", "jsonc", "json"],
+    match: ["html"],
     command: "vscode-html-language-server",
     args: ["--stdio"],
     rootMarkers: ["package.json"],
     languageId: "html",
   },
+  {
+    id: "vscode-css-language-server",
+    match: ["css", "scss", "less"],
+    command: "vscode-css-language-server",
+    args: ["--stdio"],
+    rootMarkers: ["package.json"],
+    languageId: "css",
+  },
+  {
+    id: "vscode-json-language-server",
+    match: ["json", "jsonc", "jsonl"],
+    command: "vscode-json-language-server",
+    args: ["--stdio"],
+    rootMarkers: ["package.json"],
+    languageId: "json",
+  },
+  {
+    id: "bash-language-server",
+    match: ["sh", "bash"],
+    command: "bash-language-server",
+    args: ["start"],
+    rootMarkers: [".git"],
+    languageId: "shellscript",
+  },
+  {
+    id: "sqls",
+    match: ["sql"],
+    command: "sqls",
+    args: [],
+    rootMarkers: [".git"],
+    languageId: "sql",
+  },
   {
     id: "nil",
     match: ["nix"],
@@ -64,5 +153,6 @@ export const servers: ServerConfig[] = [
     args: ["--lsp"],
     rootMarkers: [".oxlintrc.json", "oxlint.config.json"],
     languageId: "typescript",
+    diagnosticsOnly: true,
   },
 ];

src/client.ts

@@ -7,38 +7,16 @@ import {
   type MessageConnection,
 } from "vscode-jsonrpc/node.js";
 import type {
+  FileSystemWatcher,
   InitializeParams,
   PublishDiagnosticsParams,
+  Registration,
+  Unregistration,
 } from "vscode-languageserver-protocol";
-import * as path from "node:path";
 import type { ServerConfig } from "./types.ts";
 import { ServerNotFoundError } from "./types.ts";
 import { findRoot, pathToUri, uriToPath } from "./root.ts";
-
-// Is On PATH - Returns true if `cmd` resolves to an executable via the
-// supplied PATH. Absolute/relative paths are checked directly.
-function isOnPath(cmd: string, env: NodeJS.ProcessEnv): boolean {
-  const isExec = (p: string) => {
-    try {
-      fs.accessSync(p, fs.constants.X_OK);
-      return true;
-    } catch {
-      return false;
-    }
-  };
-  if (cmd.includes(path.sep)) return isExec(cmd);
-  const exts =
-    process.platform === "win32"
-      ? (env.PATHEXT ?? ".EXE;.CMD;.BAT").split(";")
-      : [""];
-  for (const dir of (env.PATH ?? "").split(path.delimiter)) {
-    if (!dir) continue;
-    for (const ext of exts) {
-      if (isExec(path.join(dir, cmd + ext))) return true;
-    }
-  }
-  return false;
-}
+import { isOnPath } from "./util.ts";
 
 // LspClient - Thin wrapper that spawns a language server, performs the
 // initialize handshake, auto-opens a file, and exposes sendRequest so the
@@ -65,6 +43,8 @@ export class LspClient {
   // version numbers in didOpen/didChange. We track them so the daemon
   // can resync files via notifyChange after on-disk edits.
   private versions = new Map<string, number>();
+  private fileWatchers = new Map<string, FileSystemWatcher[]>();
+  private watchersListeners = new Set<() => void>();
 
   constructor(private readonly server: ServerConfig) {}
 
@@ -127,11 +107,47 @@ export class LspClient {
         }
       },
     );
-    // Accept Common Server Requests - Return empty/null so servers don't
-    // stall. Good enough for a CLI; a real client would answer properly.
-    this.conn.onRequest("workspace/configuration", () => []);
-    this.conn.onRequest("client/registerCapability", () => null);
-    this.conn.onRequest("client/unregisterCapability", () => null);
+    // Accept Common Server Requests - Return one configuration response per
+    // requested item. Server-specific settings live in server.ts so adding
+    // another picky server doesn't grow conditionals in this transport layer.
+    this.conn.onRequest(
+      "workspace/configuration",
+      (params: { items?: { section?: string }[] }) => {
+        const items = params.items ?? [];
+        const config = this.server.workspaceConfiguration;
+        return items.map((item) =>
+          config?.getSection?.(item.section, { rootDir, env }) ?? null,
+        );
+      },
+    );
+    this.conn.onRequest(
+      "client/registerCapability",
+      (params: { registrations?: Registration[] }) => {
+        let changed = false;
+        for (const reg of params.registrations ?? []) {
+          if (reg.method !== "workspace/didChangeWatchedFiles") continue;
+          const opts = reg.registerOptions as
+            | { watchers?: FileSystemWatcher[] }
+            | undefined;
+          this.fileWatchers.set(reg.id, opts?.watchers ?? []);
+          changed = true;
+        }
+        if (changed) for (const l of this.watchersListeners) l();
+        return null;
+      },
+    );
+    this.conn.onRequest(
+      "client/unregisterCapability",
+      (params: { unregisterations?: Unregistration[] }) => {
+        let changed = false;
+        for (const unreg of params.unregisterations ?? []) {
+          if (unreg.method !== "workspace/didChangeWatchedFiles") continue;
+          if (this.fileWatchers.delete(unreg.id)) changed = true;
+        }
+        if (changed) for (const l of this.watchersListeners) l();
+        return null;
+      },
+    );
 
     this.conn.listen();
 
@@ -150,7 +166,11 @@ export class LspClient {
           publishDiagnostics: {},
           synchronization: { didSave: true },
         },
-        workspace: { workspaceFolders: true, configuration: true },
+        workspace: {
+          workspaceFolders: true,
+          configuration: true,
+          didChangeWatchedFiles: { dynamicRegistration: true },
+        },
       },
     };
     await this.conn.sendRequest("initialize", {
@@ -161,6 +181,16 @@ export class LspClient {
       },
     });
     this.conn.sendNotification("initialized", {});
+
+    // Push Configuration - Some servers do not always request workspace/configuration,
+    // but still consume settings delivered through didChangeConfiguration.
+    const settings = this.server.workspaceConfiguration?.initialSettings?.({
+      rootDir,
+      env,
+    });
+    if (settings !== undefined && settings !== null) {
+      this.conn.sendNotification("workspace/didChangeConfiguration", { settings });
+    }
   }
 
   // Wait For Ready - Resolves when there are no outstanding progress
@@ -217,11 +247,34 @@ export class LspClient {
     return uri;
   }
 
+  closeDocument(uri: string): void {
+    this.versions.delete(uri);
+    this.diagnostics.delete(uri);
+    this.conn.sendNotification("textDocument/didClose", {
+      textDocument: { uri },
+    });
+  }
+
   // Send Raw LSP Request - Passthrough used by the command dispatcher.
   sendRequest<R = unknown>(method: string, params: unknown): Promise<R> {
     return this.conn.sendRequest(method, params) as Promise<R>;
   }
 
+  sendNotification(method: string, params: unknown): void {
+    this.conn.sendNotification(method, params);
+  }
+
+  getFileWatchers(): FileSystemWatcher[] {
+    return Array.from(this.fileWatchers.values()).flat();
+  }
+
+  onWatchersChanged(listener: () => void): () => void {
+    this.watchersListeners.add(listener);
+    return () => {
+      this.watchersListeners.delete(listener);
+    };
+  }
+
   // Clear Diagnostics - Drops the cached diagnostics for a URI so callers
   // can force waitForDiagnostics to await a fresh publish after didChange.
   clearDiagnostics(uri: string): void {

src/config.ts

@@ -0,0 +1,141 @@
+// Per-Repo Config - Loads `.pi-lsp.json` from the nearest ancestor of a
+// given path and merges it with the built-in server registry. Config is a
+// JSON file shaped like:
+//
+//   {
+//     "servers": [
+//       { "id": "rust-analyzer", "match": ["rs"], "command": "rust-analyzer",
+//         "args": [], "rootMarkers": ["Cargo.toml"], "languageId": "rust" },
+//       { "id": "gopls", "args": ["-remote=auto", "-vv"] }
+//     ],
+//     "disable": ["oxlint"]
+//   }
+//
+// Merge Semantics:
+//   - Entries whose `id` matches a built-in shallow-merge their fields (user wins).
+//   - Entries with a new `id` append, and must include all required fields.
+//   - The `disable` list filters the merged result by id.
+//
+// Caching: Resolved lists are cached per config-file path and invalidated by
+// mtime. If no config file exists, the built-in registry is returned.
+import * as fs from "node:fs";
+import * as path from "node:path";
+import { servers as builtinServers } from "../server.ts";
+import type { ServerConfig } from "./types.ts";
+
+const CONFIG_FILE = ".pi-lsp.json";
+
+interface PiLspConfig {
+  servers?: Array<Partial<ServerConfig> & { id: string }>;
+  disable?: string[];
+}
+
+interface CacheEntry {
+  mtimeMs: number;
+  resolved: ServerConfig[];
+}
+
+const cache = new Map<string, CacheEntry>();
+
+// Find Config File - Walks upward from `fromDir` looking for `.pi-lsp.json`.
+// Returns the absolute path or null if none found before the filesystem root.
+function findConfigFile(fromDir: string): string | null {
+  let dir = path.resolve(fromDir);
+  const { root } = path.parse(dir);
+  while (true) {
+    const candidate = path.join(dir, CONFIG_FILE);
+    if (fs.existsSync(candidate)) return candidate;
+    if (dir === root) return null;
+    dir = path.dirname(dir);
+  }
+}
+
+// Merge Config - Built-ins by id, user overrides shallow-merge in, new ids
+// append (with required-field validation), and `disable` filters the result.
+function mergeConfig(config: PiLspConfig, sourcePath: string): ServerConfig[] {
+  const byId = new Map<string, ServerConfig>(
+    builtinServers.map((s) => [s.id, { ...s }]),
+  );
+
+  // Apply Overrides And New Servers
+  for (const override of config.servers ?? []) {
+    if (!override.id || typeof override.id !== "string") {
+      throw new Error(
+        `pi-lsp config (${sourcePath}): every entry in "servers" must have a string "id"`,
+      );
+    }
+    const existing = byId.get(override.id);
+    if (existing) {
+      byId.set(override.id, { ...existing, ...override } as ServerConfig);
+    } else {
+      // New Server - Must include all required spawn fields.
+      const required = ["match", "command", "args", "rootMarkers"] as const;
+      const missing = required.filter((k) => override[k] === undefined);
+      if (missing.length > 0) {
+        throw new Error(
+          `pi-lsp config (${sourcePath}): new server "${override.id}" is missing required field(s): ${missing.join(", ")}`,
+        );
+      }
+      byId.set(override.id, override as ServerConfig);
+    }
+  }
+
+  // Apply Disable Filter
+  const disabled = new Set(config.disable ?? []);
+  return Array.from(byId.values()).filter((s) => !disabled.has(s.id));
+}
+
+// Get Servers For Path - Returns the merged ServerConfig list applicable to
+// `fromDir` (or the directory containing a file path). Cached per config-file
+// path with mtime invalidation. On parse/merge failure, logs to stderr and
+// falls back to the built-in registry so a broken config never breaks LSP.
+export function getServersForPath(fromPath: string): ServerConfig[] {
+  // Resolve To Directory - Accept either a file path or a directory.
+  let dir = path.resolve(fromPath);
+  try {
+    const st = fs.statSync(dir);
+    if (!st.isDirectory()) dir = path.dirname(dir);
+  } catch {
+    dir = path.dirname(dir);
+  }
+
+  const configPath = findConfigFile(dir);
+  if (!configPath) return builtinServers;
+
+  let mtimeMs: number;
+  try {
+    mtimeMs = fs.statSync(configPath).mtimeMs;
+  } catch {
+    return builtinServers;
+  }
+
+  const cached = cache.get(configPath);
+  if (cached && cached.mtimeMs === mtimeMs) return cached.resolved;
+
+  let parsed: PiLspConfig;
+  try {
+    const raw = fs.readFileSync(configPath, "utf8");
+    parsed = JSON.parse(raw);
+  } catch (err) {
+    process.stderr.write(
+      `pi-lsp: failed to read/parse ${configPath}: ${(err as Error).message}\n`,
+    );
+    return builtinServers;
+  }
+
+  let resolved: ServerConfig[];
+  try {
+    resolved = mergeConfig(parsed, configPath);
+  } catch (err) {
+    process.stderr.write(`pi-lsp: ${(err as Error).message}\n`);
+    return builtinServers;
+  }
+
+  cache.set(configPath, { mtimeMs, resolved });
+  return resolved;
+}
+
+// Clear Config Cache - Test hook; not used in production.
+export function clearConfigCache(): void {
+  cache.clear();
+}

src/daemon.ts

@@ -5,9 +5,11 @@
 import * as fs from "node:fs";
 import * as net from "node:net";
 import * as path from "node:path";
+import type { FileSystemWatcher } from "vscode-languageserver-protocol";
 import { LspClient } from "./client.ts";
-import { findRoot, pickServer, pathToUri } from "./root.ts";
+import { findRoot, findServerById, pathToUri } from "./root.ts";
 import type { ServerConfig } from "./types.ts";
+import { WorkspaceWatcher, type FileEvent } from "./watcher.ts";
 import {
   logPath,
   socketPath,
@@ -17,8 +19,12 @@ import {
   type LaunchContext,
 } from "./daemonProtocol.ts";
 
-// Default Idle TTL - 5 minutes. Per-server overrides via ServerConfig.idleTtlMs.
 const DEFAULT_IDLE_TTL_MS = 5 * 60 * 1000;
+const WATCHER_READY_TIMEOUT_MS = 5000;
+const FILE_CHANGE_DELETED = 3;
+const WATCH_KIND_CREATE = 1;
+const WATCH_KIND_CHANGE = 2;
+const WATCH_KIND_DELETE = 4;
 
 // Client Entry - One LspClient per (server.id, rootDir), plus the bookkeeping
 // needed to keep files in sync and evict on idleness.
@@ -37,6 +43,9 @@ interface ClientEntry {
   idleTimer: NodeJS.Timeout | null;
   ttlMs: number;
   lastUsed: number;
+  watcher: WorkspaceWatcher | null;
+  unsubscribeWatchers: (() => void) | null;
+  usesDerivedWatchers: boolean;
 }
 
 const entries = new Map<string, ClientEntry>();
@@ -50,14 +59,17 @@ function log(...args: unknown[]) {
   );
 }
 
-// Get Or Create Entry - Looks up the cached client for a file, spawning a
-// fresh LspClient if needed. The returned entry is guaranteed to have its
-// `ready` promise resolved before the caller uses it.
+// Get Or Create Entry - Looks up the cached client for a server+file,
+// spawning a fresh LspClient if needed. The returned entry is guaranteed
+// to have its `ready` promise resolved before the caller uses it. The
+// server registry is resolved against any `.pi-lsp.json` reachable from
+// `filePath`, so per-repo config overrides take effect at spawn time.
 async function getOrCreateEntry(
   filePath: string,
+  serverId: string,
   launch: LaunchContext,
 ): Promise<ClientEntry> {
-  const server = pickServer(filePath);
+  const server = findServerById(filePath, serverId);
   const rootDir = findRoot(filePath, server.rootMarkers);
   const key = `${server.id}::${rootDir}`;
   const existing = entries.get(key);
@@ -85,6 +97,9 @@ async function getOrCreateEntry(
     idleTimer: null,
     ttlMs,
     lastUsed: Date.now(),
+    watcher: null,
+    unsubscribeWatchers: null,
+    usesDerivedWatchers: false,
   };
   entries.set(key, entry);
   try {
@@ -93,10 +108,104 @@ async function getOrCreateEntry(
     entries.delete(key);
     throw err;
   }
+  await attachWatcher(entry);
   bumpIdle(entry);
   return entry;
 }
 
+// Attach Watcher - Registration can happen during initialize, before the daemon subscribes.
+async function attachWatcher(entry: ClientEntry): Promise<void> {
+  if (process.env.PI_LSP_DISABLE_WATCHERS) return;
+  entry.unsubscribeWatchers = entry.client.onWatchersChanged(() => void refreshWatcher(entry));
+  await refreshWatcher(entry);
+}
+
+function watcherPatterns(entry: ClientEntry): FileSystemWatcher[] {
+  const registered = entry.client.getFileWatchers();
+  entry.usesDerivedWatchers = registered.length === 0;
+  return registered.length > 0 ? registered : derivedServerWatchers(entry.server);
+}
+
+function derivedServerWatchers(server: ServerConfig): FileSystemWatcher[] {
+  const extensions = server.match
+    .map((m) => m.replace(/^\./, ""))
+    .filter((m) => /^[A-Za-z0-9_-]+$/.test(m));
+  if (extensions.length === 0) return [];
+
+  const globPattern = extensions.length === 1
+    ? `**/*.${extensions[0]}`
+    : `**/*.{${extensions.join(",")}}`;
+  return [{
+    globPattern,
+    kind: WATCH_KIND_CREATE | WATCH_KIND_CHANGE | WATCH_KIND_DELETE,
+  }];
+}
+
+async function refreshWatcher(entry: ClientEntry): Promise<void> {
+  if (process.env.PI_LSP_DISABLE_WATCHERS) return;
+  const patterns = watcherPatterns(entry);
+  if (patterns.length === 0 && !entry.watcher) return;
+  if (!entry.watcher) {
+    entry.watcher = new WorkspaceWatcher(entry.rootDir, (events) =>
+      forwardEvents(entry, events),
+    );
+    log(`watcher`, entry.server.id, entry.rootDir, `patterns=${patterns.length}`);
+  }
+  if (process.env.LSP_DEBUG) {
+    log(`watcher patterns`, entry.server.id, JSON.stringify(patterns));
+  }
+  entry.watcher.setPatterns(patterns);
+  if (patterns.length > 0) await waitForWatcherReady(entry);
+}
+
+async function waitForWatcherReady(entry: ClientEntry): Promise<void> {
+  if (!entry.watcher) return;
+  let timeout: NodeJS.Timeout | null = null;
+  let timedOut = false;
+  try {
+    await Promise.race([
+      entry.watcher.ready(),
+      new Promise<void>((resolve) => {
+        timeout = setTimeout(() => {
+          timedOut = true;
+          resolve();
+        }, WATCHER_READY_TIMEOUT_MS);
+      }),
+    ]);
+  } finally {
+    if (timeout) clearTimeout(timeout);
+  }
+  if (timedOut) {
+    log(`watcher ready timeout`, entry.server.id, entry.rootDir);
+  }
+}
+
+function forwardEvents(entry: ClientEntry, events: FileEvent[]): void {
+  try {
+    for (const event of events) {
+      if (event.type !== FILE_CHANGE_DELETED || !entry.opened.has(event.uri)) continue;
+      entry.client.closeDocument(event.uri);
+      entry.opened.delete(event.uri);
+      void refreshWatcher(entry);
+    }
+    if (process.env.LSP_DEBUG) {
+      log(`watcher fire`, entry.server.id, JSON.stringify(events));
+    }
+    for (const uri of entry.opened.keys()) entry.client.clearDiagnostics(uri);
+    entry.client.sendNotification("workspace/didChangeWatchedFiles", {
+      changes: events,
+    });
+    if (entry.usesDerivedWatchers && entry.server.id === "typescript-language-server") {
+      void entry.client.sendRequest("workspace/executeCommand", {
+        command: "typescript.tsserverRequest",
+        arguments: ["reloadProjects"],
+      }).catch((err) => log("typescript reloadProjects failed", (err as Error).message));
+    }
+  } catch (err) {
+    log(`watcher send failed`, entry.server.id, (err as Error).message);
+  }
+}
+
 // Bump Idle - Resets the idle eviction timer. Called on every request that
 // touches the entry. We log evictions so the daemon's behavior is visible.
 function bumpIdle(entry: ClientEntry) {
@@ -110,6 +219,8 @@ function evict(entry: ClientEntry, reason: string) {
   log(`evict`, entry.key, reason);
   entries.delete(entry.key);
   if (entry.idleTimer) clearTimeout(entry.idleTimer);
+  if (entry.unsubscribeWatchers) entry.unsubscribeWatchers();
+  void entry.watcher?.dispose();
   void entry.client.dispose();
   // Auto Shutdown - If this was the last entry, there's nothing left to
   // manage. Tear down the daemon so it doesn't sit idle forever.
@@ -161,7 +272,7 @@ async function handle(req: DaemonRequest): Promise<DaemonResponse> {
     switch (req.op) {
       case "request": {
         const filePath = path.resolve(req.file);
-        const entry = await getOrCreateEntry(filePath, req.launch);
+        const entry = await getOrCreateEntry(filePath, req.serverId, req.launch);
         const { uri } = await syncFile(entry, filePath);
         bumpIdle(entry);
         const result = await entry.client.sendRequest(
@@ -172,15 +283,27 @@ async function handle(req: DaemonRequest): Promise<DaemonResponse> {
       }
       case "diagnostics": {
         const filePath = path.resolve(req.file);
-        const entry = await getOrCreateEntry(filePath, req.launch);
+        const timeoutMs = req.timeoutMs ?? 1500;
+
+        // Fan-Out - Run diagnostics against all requested servers in
+        // parallel. Individual failures are captured, not thrown.
+        const results: Record<string, unknown> = {};
+        const settled = await Promise.allSettled(
+          req.serverIds.map(async (serverId) => {
+            const entry = await getOrCreateEntry(filePath, serverId, req.launch);
             const { uri, changed } = await syncFile(entry, filePath);
             bumpIdle(entry);
             if (changed) entry.client.clearDiagnostics(uri);
-        const result = await entry.client.waitForDiagnostics(
-          uri,
-          req.timeoutMs ?? 1500,
+            const diag = await entry.client.waitForDiagnostics(uri, timeoutMs);
+            return { serverId, diag };
+          }),
         );
-        return { id: req.id, ok: true, result };
+        for (const outcome of settled) {
+          if (outcome.status === "fulfilled") {
+            results[outcome.value.serverId] = outcome.value.diag;
+          }
+        }
+        return { id: req.id, ok: true, result: results };
       }
       case "status": {
         const result = {
@@ -277,6 +400,8 @@ function shutdownDaemon(reason: string) {
   if (server) server.close();
   for (const entry of entries.values()) {
     if (entry.idleTimer) clearTimeout(entry.idleTimer);
+    if (entry.unsubscribeWatchers) entry.unsubscribeWatchers();
+    void entry.watcher?.dispose();
     void entry.client.dispose();
   }
   entries.clear();

src/daemonClient.ts

@@ -22,6 +22,7 @@ function unwrap(resp: DaemonResponse): unknown {
 // daemon injects textDocument.uri from `file`, so callers omit it.
 export async function daemonRequest(
   file: string,
+  serverId: string,
   method: string,
   params: Record<string, unknown>,
 ): Promise<unknown> {
@@ -29,6 +30,7 @@ export async function daemonRequest(
     await sendOnce({
       op: "request",
       file,
+      serverId,
       method,
       params,
       launch: buildLaunchContext(),
@@ -38,14 +40,18 @@ export async function daemonRequest(
 
 // Wait For Diagnostics - Diagnostics arrive as a notification, not a
 // response, so the daemon has a dedicated op that awaits the next publish.
+// Accepts an array of server IDs; daemon fans out in parallel and returns
+// a grouped map: { [serverId]: { uri, diagnostics[] } }.
 export async function daemonDiagnostics(
   file: string,
+  serverIds: string[],
   timeoutMs = 1500,
 ): Promise<unknown> {
   return unwrap(
     await sendOnce({
       op: "diagnostics",
       file,
+      serverIds,
       timeoutMs,
       launch: buildLaunchContext(),
     }),

src/daemonProtocol.ts

@@ -38,6 +38,7 @@ export type DaemonRequest =
       id: number;
       op: "request";
       file: string;
+      serverId: string;
       method: string;
       params: Record<string, unknown>;
       launch: LaunchContext;
@@ -46,6 +47,7 @@ export type DaemonRequest =
       id: number;
       op: "diagnostics";
       file: string;
+      serverIds: string[];
       timeoutMs?: number;
       launch: LaunchContext;
     }
@@ -57,6 +59,7 @@ export type DaemonRequestWithoutId =
   | {
       op: "request";
       file: string;
+      serverId: string;
       method: string;
       params: Record<string, unknown>;
       launch: LaunchContext;
@@ -64,6 +67,7 @@ export type DaemonRequestWithoutId =
   | {
       op: "diagnostics";
       file: string;
+      serverIds: string[];
       timeoutMs?: number;
       launch: LaunchContext;
     }

src/root.ts

@@ -1,9 +1,15 @@
 import * as fs from "node:fs";
 import * as path from "node:path";
 import { pathToFileURL, fileURLToPath } from "node:url";
-import { servers, globalRootMarkers } from "../server.ts";
+import { globalRootMarkers } from "../server.ts";
+import { getServersForPath } from "./config.ts";
 import type { ServerConfig } from "./types.ts";
 import { UnsupportedExtensionError } from "./types.ts";
+import { isOnPath } from "./util.ts";
+
+// Re-Export - Centralizes the path-aware registry helper so callers can
+// import it from `./root.ts` alongside pickServer/findRoot.
+export { getServersForPath };
 
 // Resolve File URI To Local Path
 export function uriToPath(uri: string): string {
@@ -15,17 +21,45 @@ export function pathToUri(p: string): string {
   return pathToFileURL(path.resolve(p)).toString();
 }
 
+// Server Availability Cache - Checked once per process lifetime per server.
+// Avoids repeated filesystem lookups on every tool call.
+const serverAvailability = new Map<string, boolean>();
+
+// Is Server Available - Returns true if the server binary is on PATH.
+// Result is cached for the lifetime of this process.
+export function isServerAvailable(server: ServerConfig): boolean {
+  if (serverAvailability.has(server.id)) return serverAvailability.get(server.id)!;
+  const available = isOnPath(server.command, process.env);
+  serverAvailability.set(server.id, available);
+  return available;
+}
+
 // Pick Server By File Extension - match[] entries are matched against the
-// file's extension (no dot). First server in the registry wins.
+// file's extension (no dot). First available, non-diagnosticsOnly server wins.
+// Resolves the per-repo config from the file's directory before matching.
 export function pickServer(filePath: string): ServerConfig {
   const ext = path.extname(filePath).replace(/^\./, "");
-  const hit = servers.find((s) => s.match.includes(ext));
+  const list = getServersForPath(filePath);
+  const hit = list.find((s) => s.match.includes(ext) && !s.diagnosticsOnly && isServerAvailable(s));
   if (!hit) {
     throw new UnsupportedExtensionError(`.${ext}`);
   }
   return hit;
 }
 
+// Find Server By ID - Looks up a ServerConfig by id within the registry
+// resolved for the given path. Throws if the id is not registered.
+export function findServerById(filePath: string, id: string): ServerConfig {
+  const list = getServersForPath(filePath);
+  const hit = list.find((s) => s.id === id);
+  if (!hit) {
+    throw new Error(
+      `Unknown server ID: "${id}". Registered: ${list.map((s) => s.id).join(", ")}`,
+    );
+  }
+  return hit;
+}
+
 // Find Project Root By Walking Upward - stops at the first directory
 // containing any rootMarker. Falls back to the file's directory.
 export function findRoot(filePath: string, markers: string[]): string {

src/types.ts

@@ -17,6 +17,22 @@ export class ServerNotFoundError extends Error {
   }
 }
 
+export interface WorkspaceConfigurationContext {
+  rootDir: string;
+  env: NodeJS.ProcessEnv;
+}
+
+export interface ServerWorkspaceConfiguration {
+  // Initial Settings - Optional payload pushed via workspace/didChangeConfiguration
+  // after initialize/initialized for servers that don't always request config.
+  initialSettings?: (ctx: WorkspaceConfigurationContext) => unknown;
+  // Section Settings - Optional handler for workspace/configuration requests.
+  getSection?: (
+    section: string | undefined,
+    ctx: WorkspaceConfigurationContext,
+  ) => unknown;
+}
+
 export interface ServerConfig {
   // Stable identifier (useful for logs and future daemon cache keys).
   id: string;
@@ -34,6 +50,13 @@ export interface ServerConfig {
   // Idle TTL - Daemon keeps one server alive per (id, rootDir) and evicts
   // it after this many ms of inactivity. Defaults to 5 minutes.
   idleTtlMs?: number;
+  // Diagnostics Only - When true, this server is excluded from
+  // hover/definition/references/completion/documentSymbol but included
+  // in lsp_diagnostics and auto-check.
+  diagnosticsOnly?: boolean;
+  // Workspace Configuration - Optional server-specific settings exposed through
+  // workspace/configuration and workspace/didChangeConfiguration.
+  workspaceConfiguration?: ServerWorkspaceConfiguration;
 }
 
 // Supported high-level commands exposed via the CLI. Extend this union

src/util.ts

@@ -0,0 +1,27 @@
+import * as fs from "node:fs";
+import * as path from "node:path";
+
+// Is On PATH - Returns true if `cmd` resolves to an executable via the
+// supplied PATH. Absolute/relative paths are checked directly.
+export function isOnPath(cmd: string, env: NodeJS.ProcessEnv): boolean {
+  const isExec = (p: string) => {
+    try {
+      fs.accessSync(p, fs.constants.X_OK);
+      return true;
+    } catch {
+      return false;
+    }
+  };
+  if (cmd.includes(path.sep)) return isExec(cmd);
+  const exts =
+    process.platform === "win32"
+      ? (env.PATHEXT ?? ".EXE;.CMD;.BAT").split(";")
+      : [""];
+  for (const dir of (env.PATH ?? "").split(path.delimiter)) {
+    if (!dir) continue;
+    for (const ext of exts) {
+      if (isExec(path.join(dir, cmd + ext))) return true;
+    }
+  }
+  return false;
+}

src/watcher.ts

@@ -0,0 +1,237 @@
+import * as fs from "node:fs";
+import * as path from "node:path";
+import chokidar, { type FSWatcher } from "chokidar";
+import ignore, { type Ignore } from "ignore";
+import picomatch from "picomatch";
+import type { FileSystemWatcher } from "vscode-languageserver-protocol";
+import { pathToUri } from "./root.ts";
+
+const FILE_CHANGE_CREATED = 1;
+const FILE_CHANGE_CHANGED = 2;
+const FILE_CHANGE_DELETED = 3;
+
+const WATCH_KIND_CREATE = 1;
+const WATCH_KIND_CHANGE = 2;
+const WATCH_KIND_DELETE = 4;
+
+const DEBOUNCE_QUIET_MS = 50;
+const DEBOUNCE_MAX_WAIT_MS = 500;
+
+export const BASELINE_IGNORES = [
+  "**/.git/**",
+  "**/.DS_Store",
+  "**/.hg/**",
+  "**/.svn/**",
+];
+
+const NO_GITIGNORE_FALLBACK = ["**/node_modules/**", "**/.git/**"];
+
+export interface FileEvent {
+  uri: string;
+  type: 1 | 2 | 3;
+}
+
+function buildIgnoreMatcher(rootDir: string): (relPath: string) => boolean {
+  const gitignorePath = path.join(rootDir, ".gitignore");
+  let ig: Ignore | null = null;
+  if (fs.existsSync(gitignorePath)) {
+    try {
+      ig = ignore().add(fs.readFileSync(gitignorePath, "utf8"));
+    } catch {
+      ig = null;
+    }
+  }
+
+  const baselineMatcher = picomatch(BASELINE_IGNORES);
+  if (ig) {
+    return (relPath) => {
+      if (baselineMatcher(relPath)) return true;
+      const posixRel = relPath.split(path.sep).join("/");
+      if (!posixRel || posixRel === ".") return false;
+      return ig.ignores(posixRel);
+    };
+  }
+
+  const fallbackMatcher = picomatch(NO_GITIGNORE_FALLBACK);
+  return (relPath) => baselineMatcher(relPath) || fallbackMatcher(relPath);
+}
+
+function compileWatchers(
+  watchers: FileSystemWatcher[],
+  rootDir: string,
+): (relPath: string, absPath: string) => number {
+  const compiled = watchers.map((w) => {
+    const pattern = typeof w.globPattern === "string"
+      ? w.globPattern
+      : resolveRelativePattern(w.globPattern, rootDir);
+    return {
+      match: picomatch(pattern, { dot: true }),
+      kind: w.kind ?? (WATCH_KIND_CREATE | WATCH_KIND_CHANGE | WATCH_KIND_DELETE),
+    };
+  });
+
+  return (relPath, absPath) => {
+    const posixRel = relPath.split(path.sep).join("/");
+    const posixAbs = absPath.split(path.sep).join("/");
+    let kind = 0;
+    for (const c of compiled) {
+      if (c.match(posixRel) || c.match(posixAbs)) kind |= c.kind;
+    }
+    return kind;
+  };
+}
+
+// Relative Pattern - Servers may send baseUri as a string or WorkspaceFolder.
+function resolveRelativePattern(
+  rp: { baseUri: string | { uri: string }; pattern: string },
+  rootDir: string,
+): string {
+  const baseUri = typeof rp.baseUri === "string" ? rp.baseUri : rp.baseUri.uri;
+  if (!baseUri.startsWith("file://")) return rp.pattern;
+  const basePath = decodeURIComponent(baseUri.slice("file://".length));
+  const relBase = path.relative(rootDir, basePath);
+  if (relBase.startsWith("..") || path.isAbsolute(relBase)) return rp.pattern;
+  return relBase ? `${relBase.split(path.sep).join("/")}/${rp.pattern}` : rp.pattern;
+}
+
+export class WorkspaceWatcher {
+  private chokidar: FSWatcher | null = null;
+  private isIgnored: (relPath: string) => boolean;
+  private matchKind: (relPath: string, absPath: string) => number = () => 0;
+  private pending = new Map<string, 1 | 2 | 3>();
+  private quietTimer: NodeJS.Timeout | null = null;
+  private maxWaitTimer: NodeJS.Timeout | null = null;
+  private disposed = false;
+  private readyPromise: Promise<void> = Promise.resolve();
+  private resolveReady: (() => void) | null = null;
+
+  constructor(
+    private readonly rootDir: string,
+    private readonly onEvents: (events: FileEvent[]) => void,
+  ) {
+    this.isIgnored = buildIgnoreMatcher(rootDir);
+  }
+
+  setPatterns(watchers: FileSystemWatcher[]): void {
+    if (this.disposed) return;
+    this.matchKind = compileWatchers(watchers, this.rootDir);
+    if (watchers.length === 0) {
+      this.cancelPending();
+      void this.stopChokidar();
+      return;
+    }
+    if (!this.chokidar) this.startChokidar();
+  }
+
+  ready(): Promise<void> {
+    return this.readyPromise;
+  }
+
+  private startChokidar(): void {
+    this.readyPromise = new Promise<void>((resolve) => {
+      this.resolveReady = resolve;
+    });
+    this.chokidar = chokidar.watch(this.rootDir, {
+      ignoreInitial: true,
+      followSymlinks: false,
+      ignored: (absPath: string) => {
+        if (absPath === this.rootDir) return false;
+        const rel = path.relative(this.rootDir, absPath);
+        return this.isIgnored(rel);
+      },
+      awaitWriteFinish: { stabilityThreshold: 50, pollInterval: 25 },
+    });
+    this.chokidar.on("add", (p) => this.queue(p, FILE_CHANGE_CREATED));
+    this.chokidar.on("change", (p) => this.queue(p, FILE_CHANGE_CHANGED));
+    this.chokidar.on("unlink", (p) => this.queue(p, FILE_CHANGE_DELETED));
+    this.chokidar.on("ready", () => this.resolveReady?.());
+    this.chokidar.on("error", (err) => {
+      process.stderr.write(`[pi-lsp:watcher] ${this.rootDir}: ${String(err)}\n`);
+    });
+  }
+
+  private async stopChokidar(): Promise<void> {
+    if (!this.chokidar) return;
+    const w = this.chokidar;
+    this.chokidar = null;
+    this.resolveReady?.();
+    this.resolveReady = null;
+    this.readyPromise = Promise.resolve();
+    await w.close();
+  }
+
+  private cancelPending(): void {
+    if (this.quietTimer) clearTimeout(this.quietTimer);
+    if (this.maxWaitTimer) clearTimeout(this.maxWaitTimer);
+    this.quietTimer = null;
+    this.maxWaitTimer = null;
+    this.pending.clear();
+  }
+
+  private queue(absPath: string, type: 1 | 2 | 3): void {
+    const rel = path.relative(this.rootDir, absPath);
+    const kind = this.matchKind(rel, absPath);
+    if (kind === 0) return;
+    if (type === FILE_CHANGE_CREATED && !(kind & WATCH_KIND_CREATE)) return;
+    if (type === FILE_CHANGE_CHANGED && !(kind & WATCH_KIND_CHANGE)) return;
+    if (type === FILE_CHANGE_DELETED && !(kind & WATCH_KIND_DELETE)) return;
+
+    const uri = pathToUri(absPath);
+    const prev = this.pending.get(uri);
+    const next = coalesce(prev, type);
+    if (next === null) this.pending.delete(uri);
+    else this.pending.set(uri, next);
+    this.scheduleFlush();
+  }
+
+  private scheduleFlush(): void {
+    if (this.quietTimer) clearTimeout(this.quietTimer);
+    this.quietTimer = setTimeout(() => this.flush(), DEBOUNCE_QUIET_MS);
+    if (!this.maxWaitTimer) {
+      this.maxWaitTimer = setTimeout(() => this.flush(), DEBOUNCE_MAX_WAIT_MS);
+    }
+  }
+
+  private flush(): void {
+    if (this.quietTimer) clearTimeout(this.quietTimer);
+    if (this.maxWaitTimer) clearTimeout(this.maxWaitTimer);
+    this.quietTimer = null;
+    this.maxWaitTimer = null;
+    if (this.pending.size === 0) return;
+
+    const events: FileEvent[] = Array.from(this.pending, ([uri, type]) => ({
+      uri,
+      type,
+    }));
+    this.pending.clear();
+    try {
+      this.onEvents(events);
+    } catch (err) {
+      process.stderr.write(
+        `[pi-lsp:watcher] onEvents threw: ${(err as Error).message}\n`,
+      );
+    }
+  }
+
+  async dispose(): Promise<void> {
+    if (this.disposed) return;
+    this.disposed = true;
+    this.cancelPending();
+    await this.stopChokidar();
+  }
+}
+
+function coalesce(
+  prev: 1 | 2 | 3 | undefined,
+  next: 1 | 2 | 3,
+): 1 | 2 | 3 | null {
+  if (prev === undefined) return next;
+  if (prev === FILE_CHANGE_CREATED && next === FILE_CHANGE_DELETED) return null;
+  if (prev === FILE_CHANGE_DELETED && next === FILE_CHANGE_CREATED) {
+    return FILE_CHANGE_CHANGED;
+  }
+  if (prev === FILE_CHANGE_CREATED && next === FILE_CHANGE_CHANGED) {
+    return FILE_CHANGE_CREATED;
+  }
+  return next;
+}

test/helpers.ts

@@ -25,10 +25,11 @@ export const tsx = path.resolve(
   "cli.mjs",
 );
 
-// Unique Test Socket — each test run gets its own Unix socket so we don't
-// touch any real session daemon.
+// Unique Test Socket — each suite gets its own Unix socket so parallel
+// integration tests don't race through the same daemon.
 export function testSocket(): string {
-  return path.join(os.tmpdir(), `pi-lsp-test-${process.pid}.sock`);
+  const dir = fs.mkdtempSync(path.join(os.tmpdir(), "pi-lsp-test-"));
+  return path.join(dir, "daemon.sock");
 }
 
 // Set Test Socket — sets PI_LSP_SOCKET_PATH for the current process and
@@ -39,7 +40,7 @@ export function setTestSocket(env: Record<string, string | undefined>): () => vo
   return () => {
     delete env.PI_LSP_SOCKET_PATH;
     try {
-      fs.unlinkSync(sock);
+      fs.rmSync(path.dirname(sock), { recursive: true, force: true });
     } catch {
       // Socket may not exist — that's fine.
     }

test/integration/cli-daemon.test.ts

@@ -13,15 +13,15 @@ describe("cli daemon lifecycle", () => {
   const env = { ...process.env };
   let cleanup: () => void;
 
-  before(() => {
+  before(async () => {
     cleanup = setTestSocket(env);
     // Stop any stale daemon on this socket before tests run.
-    stopTestDaemon(env);
+    await stopTestDaemon(env);
   });
 
-  after(() => {
+  after(async () => {
     // Tear down daemon and clean up socket after all tests.
-    stopTestDaemon(env);
+    await stopTestDaemon(env);
     cleanup();
   });
 

test/integration/watcher-gopls.test.ts

@@ -0,0 +1,169 @@
+import { describe, it, before, after } from "node:test";
+import * as assert from "node:assert/strict";
+import * as fs from "node:fs";
+import * as os from "node:os";
+import * as path from "node:path";
+import {
+  setTestSocket,
+  stopTestDaemon,
+  runCliJson,
+  requireServer,
+} from "../helpers.ts";
+
+const skip = requireServer("gopls");
+
+async function pollUntil<T>(
+  fn: () => Promise<T>,
+  predicate: (v: T) => boolean,
+  timeoutMs: number,
+  intervalMs = 250,
+): Promise<T> {
+  const deadline = Date.now() + timeoutMs;
+  let last: T = await fn();
+  while (Date.now() < deadline) {
+    if (predicate(last)) return last;
+    await new Promise((r) => setTimeout(r, intervalMs));
+    last = await fn();
+  }
+  return last;
+}
+
+interface DiagResult {
+  [serverId: string]: { diagnostics?: { message: string }[] };
+}
+
+describe("watcher: gopls picks up external file changes", { skip: skip ?? undefined }, () => {
+  let tmpDir: string;
+  let mainFile: string;
+  let helperFile: string;
+  const env = { ...process.env };
+  let cleanup: () => void;
+
+  before(async () => {
+    cleanup = setTestSocket(env);
+    await stopTestDaemon(env);
+
+    tmpDir = fs.mkdtempSync(path.join(os.tmpdir(), "pi-lsp-gopls-watch-"));
+    fs.writeFileSync(path.join(tmpDir, "go.mod"), "module example.com/wtest\n\ngo 1.21\n");
+    mainFile = path.join(tmpDir, "main.go");
+    helperFile = path.join(tmpDir, "helper.go");
+    fs.writeFileSync(
+      mainFile,
+      "package main\n\nfunc main() {\n\tHelper()\n}\n",
+    );
+  });
+
+  after(async () => {
+    await stopTestDaemon(env);
+    cleanup();
+    fs.rmSync(tmpDir, { recursive: true, force: true });
+  });
+
+  it("initially reports undefined symbol", async () => {
+    const result = await pollUntil(
+      async () =>
+        (await runCliJson(
+          [mainFile, "diagnostics", '{"timeoutMs":3000}'],
+          env,
+        )) as DiagResult,
+      (r) => {
+        const diags = r["gopls"]?.diagnostics ?? [];
+        return diags.some(
+          (d) =>
+            d.message.toLowerCase().includes("undefined") ||
+            d.message.includes("Helper"),
+        );
+      },
+      15000,
+      500,
+    );
+    const diags = result["gopls"]?.diagnostics ?? [];
+    const hasUndefined = diags.some((d) =>
+      d.message.toLowerCase().includes("undefined") || d.message.includes("Helper"),
+    );
+    assert.ok(
+      hasUndefined,
+      `Expected undefined-symbol diagnostic, got: ${JSON.stringify(diags)}`,
+    );
+  });
+
+  it("clears the diagnostic after helper.go is created externally", async () => {
+    fs.writeFileSync(
+      helperFile,
+      "package main\n\nfunc Helper() {}\n",
+    );
+
+    const result = await pollUntil(
+      async () =>
+        (await runCliJson(
+          [mainFile, "diagnostics", '{"timeoutMs":3000}'],
+          env,
+        )) as DiagResult,
+      (r) => {
+        const diags = r["gopls"]?.diagnostics ?? [];
+        return !diags.some(
+          (d) =>
+            d.message.toLowerCase().includes("undefined") ||
+            d.message.includes("Helper"),
+        );
+      },
+      15000,
+      500,
+    );
+
+    const finalDiags = result["gopls"]?.diagnostics ?? [];
+    const stillUndefined = finalDiags.some(
+      (d) =>
+        d.message.toLowerCase().includes("undefined") ||
+        d.message.includes("Helper"),
+    );
+    assert.ok(
+      !stillUndefined,
+      `Expected diagnostic to clear after creating helper.go, still got: ${JSON.stringify(finalDiags)}`,
+    );
+  });
+
+  it("closes an opened file when it is deleted externally", async () => {
+    fs.writeFileSync(
+      helperFile,
+      "package main\n\nfunc Helper(x int) {}\n",
+    );
+    await runCliJson([helperFile, "diagnostics", '{"timeoutMs":3000}'], env);
+
+    await pollUntil(
+      async () =>
+        (await runCliJson(
+          [mainFile, "diagnostics", '{"timeoutMs":3000}'],
+          env,
+        )) as DiagResult,
+      (r) => {
+        const diags = r["gopls"]?.diagnostics ?? [];
+        return diags.some((d) => d.message.includes("not enough arguments"));
+      },
+      15000,
+      500,
+    );
+
+    fs.rmSync(helperFile);
+
+    const result = await pollUntil(
+      async () =>
+        (await runCliJson(
+          [mainFile, "diagnostics", '{"timeoutMs":3000}'],
+          env,
+        )) as DiagResult,
+      (r) => {
+        const diags = r["gopls"]?.diagnostics ?? [];
+        return diags.some((d) => d.message.toLowerCase().includes("undefined"));
+      },
+      15000,
+      500,
+    );
+
+    const finalDiags = result["gopls"]?.diagnostics ?? [];
+    assert.ok(
+      finalDiags.some((d) => d.message.toLowerCase().includes("undefined")),
+      `Expected undefined-symbol diagnostic after deleting opened helper.go, got: ${JSON.stringify(finalDiags)}`,
+    );
+  });
+});

test/integration/watcher-typescript.test.ts

@@ -0,0 +1,143 @@
+import { describe, it, before, after } from "node:test";
+import * as assert from "node:assert/strict";
+import * as fs from "node:fs";
+import * as os from "node:os";
+import * as path from "node:path";
+import {
+  setTestSocket,
+  stopTestDaemon,
+  runCliJson,
+  requireServer,
+} from "../helpers.ts";
+
+const skip = requireServer("typescript-language-server");
+
+async function pollUntil<T>(
+  fn: () => Promise<T>,
+  predicate: (v: T) => boolean,
+  timeoutMs: number,
+  intervalMs = 250,
+): Promise<T> {
+  const deadline = Date.now() + timeoutMs;
+  let last: T = await fn();
+  while (Date.now() < deadline) {
+    if (predicate(last)) return last;
+    await new Promise((r) => setTimeout(r, intervalMs));
+    last = await fn();
+  }
+  return last;
+}
+
+interface DiagResult {
+  [serverId: string]: { diagnostics?: { message: string }[] };
+}
+
+describe("watcher: typescript handles derived file patterns", { skip: skip ?? undefined }, () => {
+  let tmpDir: string;
+  let mainFile: string;
+  let helperFile: string;
+  const env = { ...process.env };
+  let cleanup: () => void;
+
+  before(async () => {
+    delete env.NODE_OPTIONS;
+    cleanup = setTestSocket(env);
+    await stopTestDaemon(env);
+
+    tmpDir = fs.mkdtempSync(path.join(os.tmpdir(), "pi-lsp-ts-watch-"));
+    fs.writeFileSync(
+      path.join(tmpDir, ".pi-lsp.json"),
+      JSON.stringify({ disable: ["oxlint"] }),
+    );
+    fs.writeFileSync(
+      path.join(tmpDir, "tsconfig.json"),
+      JSON.stringify(
+        {
+          compilerOptions: {
+            target: "ES2022",
+            module: "ESNext",
+            moduleResolution: "Bundler",
+            strict: true,
+            noEmit: true,
+          },
+          include: ["*.ts"],
+        },
+        null,
+        2,
+      ),
+    );
+    mainFile = path.join(tmpDir, "main.ts");
+    helperFile = path.join(tmpDir, "helper.ts");
+    fs.writeFileSync(
+      mainFile,
+      'import { helper } from "./helper";\n\nconsole.log(helper());\n',
+    );
+    fs.writeFileSync(helperFile, "export function helper(): number {\n  return 1;\n}\n");
+  });
+
+  after(async () => {
+    await stopTestDaemon(env);
+    cleanup();
+    fs.rmSync(tmpDir, { recursive: true, force: true });
+  });
+
+  it("clears missing module after an unopened imported file is created", async () => {
+    fs.rmSync(helperFile);
+
+    const missing = (await runCliJson(
+      [mainFile, "diagnostics", '{"timeoutMs":5000}'],
+      env,
+    )) as DiagResult;
+    assert.ok(
+      (missing["typescript-language-server"]?.diagnostics ?? []).some((d) =>
+        d.message.includes("Cannot find module './helper'")
+      ),
+    );
+
+    fs.writeFileSync(helperFile, "export function helper(): number {\n  return 1;\n}\n");
+
+    const result = await pollUntil(
+      async () =>
+        (await runCliJson(
+          [mainFile, "diagnostics", '{"timeoutMs":3000}'],
+          env,
+        )) as DiagResult,
+      (r) => (r["typescript-language-server"]?.diagnostics ?? []).length === 0,
+      15000,
+      500,
+    );
+
+    assert.deepEqual(result["typescript-language-server"]?.diagnostics ?? [], []);
+  });
+
+  it("reports missing module after an opened imported file is deleted", async () => {
+    const initial = (await runCliJson(
+      [mainFile, "diagnostics", '{"timeoutMs":5000}'],
+      env,
+    )) as DiagResult;
+    assert.deepEqual(initial["typescript-language-server"]?.diagnostics ?? [], []);
+
+    await runCliJson([helperFile, "diagnostics", '{"timeoutMs":5000}'], env);
+    fs.rmSync(helperFile);
+
+    const result = await pollUntil(
+      async () =>
+        (await runCliJson(
+          [mainFile, "diagnostics", '{"timeoutMs":3000}'],
+          env,
+        )) as DiagResult,
+      (r) => {
+        const diags = r["typescript-language-server"]?.diagnostics ?? [];
+        return diags.some((d) => d.message.includes("Cannot find module './helper'"));
+      },
+      15000,
+      500,
+    );
+
+    const diags = result["typescript-language-server"]?.diagnostics ?? [];
+    assert.ok(
+      diags.some((d) => d.message.includes("Cannot find module './helper'")),
+      `Expected missing-module diagnostic after deleting opened helper.ts, got: ${JSON.stringify(diags)}`,
+    );
+  });
+});

test/unit/config.test.ts

@@ -0,0 +1,130 @@
+// Config Unit Tests — getServersForPath() merge semantics, mtime caching,
+// and graceful fallback on parse errors.
+import { describe, it, beforeEach, afterEach } from "node:test";
+import * as assert from "node:assert/strict";
+import * as fs from "node:fs";
+import * as os from "node:os";
+import * as path from "node:path";
+import { getServersForPath, clearConfigCache } from "../../src/config.ts";
+import { servers as builtinServers } from "../../server.ts";
+
+let tmpDir: string;
+
+beforeEach(() => {
+  tmpDir = fs.mkdtempSync(path.join(os.tmpdir(), "pi-lsp-config-test-"));
+  clearConfigCache();
+});
+
+afterEach(() => {
+  fs.rmSync(tmpDir, { recursive: true, force: true });
+  clearConfigCache();
+});
+
+function writeConfig(dir: string, content: unknown): void {
+  fs.writeFileSync(path.join(dir, ".pi-lsp.json"), JSON.stringify(content));
+}
+
+describe("getServersForPath", () => {
+  it("returns built-in servers when no config file is found", () => {
+    // tmpDir lives under /tmp; no ancestor will have .pi-lsp.json.
+    const result = getServersForPath(tmpDir);
+    assert.deepStrictEqual(
+      result.map((s) => s.id),
+      builtinServers.map((s) => s.id),
+    );
+  });
+
+  it("appends a new server entry from config", () => {
+    writeConfig(tmpDir, {
+      servers: [
+        {
+          id: "rust-analyzer",
+          match: ["rs"],
+          command: "rust-analyzer",
+          args: [],
+          rootMarkers: ["Cargo.toml"],
+          languageId: "rust",
+        },
+      ],
+    });
+    const result = getServersForPath(tmpDir);
+    const rust = result.find((s) => s.id === "rust-analyzer");
+    assert.ok(rust, "rust-analyzer should be present");
+    assert.deepStrictEqual(rust!.match, ["rs"]);
+    // Built-ins are still there
+    assert.ok(result.find((s) => s.id === "gopls"));
+  });
+
+  it("shallow-merges overrides into existing built-in servers", () => {
+    writeConfig(tmpDir, {
+      servers: [{ id: "gopls", args: ["-vv"] }],
+    });
+    const result = getServersForPath(tmpDir);
+    const gopls = result.find((s) => s.id === "gopls")!;
+    assert.deepStrictEqual(gopls.args, ["-vv"]);
+    // Other fields preserved from built-in
+    assert.strictEqual(gopls.command, "gopls");
+    assert.deepStrictEqual(gopls.match, ["go"]);
+  });
+
+  it("filters out servers listed in `disable`", () => {
+    writeConfig(tmpDir, { disable: ["oxlint", "gopls"] });
+    const result = getServersForPath(tmpDir);
+    assert.ok(!result.some((s) => s.id === "oxlint"));
+    assert.ok(!result.some((s) => s.id === "gopls"));
+    assert.ok(result.some((s) => s.id === "pyright"));
+  });
+
+  it("walks upward to find config in an ancestor directory", () => {
+    writeConfig(tmpDir, { disable: ["oxlint"] });
+    const sub = path.join(tmpDir, "a", "b", "c");
+    fs.mkdirSync(sub, { recursive: true });
+    const result = getServersForPath(sub);
+    assert.ok(!result.some((s) => s.id === "oxlint"));
+  });
+
+  it("accepts a file path and walks from its directory", () => {
+    writeConfig(tmpDir, { disable: ["oxlint"] });
+    const file = path.join(tmpDir, "src", "main.go");
+    fs.mkdirSync(path.dirname(file), { recursive: true });
+    fs.writeFileSync(file, "package main");
+    const result = getServersForPath(file);
+    assert.ok(!result.some((s) => s.id === "oxlint"));
+  });
+
+  it("falls back to built-ins on invalid JSON", () => {
+    fs.writeFileSync(path.join(tmpDir, ".pi-lsp.json"), "{ not valid");
+    const result = getServersForPath(tmpDir);
+    assert.deepStrictEqual(
+      result.map((s) => s.id),
+      builtinServers.map((s) => s.id),
+    );
+  });
+
+  it("falls back to built-ins when a new server is missing required fields", () => {
+    writeConfig(tmpDir, {
+      servers: [{ id: "incomplete", match: ["foo"] }],
+    });
+    const result = getServersForPath(tmpDir);
+    assert.deepStrictEqual(
+      result.map((s) => s.id),
+      builtinServers.map((s) => s.id),
+    );
+  });
+
+  it("invalidates cache on mtime change", () => {
+    writeConfig(tmpDir, { disable: ["oxlint"] });
+    let result = getServersForPath(tmpDir);
+    assert.ok(!result.some((s) => s.id === "oxlint"));
+
+    // Rewrite With Different Content And Bump mtime
+    const cfgPath = path.join(tmpDir, ".pi-lsp.json");
+    fs.writeFileSync(cfgPath, JSON.stringify({ disable: ["gopls"] }));
+    const future = new Date(Date.now() + 5000);
+    fs.utimesSync(cfgPath, future, future);
+
+    result = getServersForPath(tmpDir);
+    assert.ok(result.some((s) => s.id === "oxlint"));
+    assert.ok(!result.some((s) => s.id === "gopls"));
+  });
+});

test/unit/watcher.test.ts

@@ -0,0 +1,293 @@
+import { describe, it, before, after, beforeEach } from "node:test";
+import * as assert from "node:assert/strict";
+import * as fs from "node:fs";
+import * as os from "node:os";
+import * as path from "node:path";
+import { WorkspaceWatcher, type FileEvent } from "../../src/watcher.ts";
+import { pathToUri } from "../../src/root.ts";
+
+async function waitFor(
+  predicate: () => boolean,
+  timeoutMs = 2000,
+): Promise<boolean> {
+  const deadline = Date.now() + timeoutMs;
+  while (Date.now() < deadline) {
+    if (predicate()) return true;
+    await new Promise((r) => setTimeout(r, 25));
+  }
+  return predicate();
+}
+
+const FLUSH_WAIT_MS = 700;
+
+describe("WorkspaceWatcher", () => {
+  let tmpDir: string;
+  let received: FileEvent[][] = [];
+  let watcher: WorkspaceWatcher | null = null;
+
+  before(() => {
+    tmpDir = fs.mkdtempSync(path.join(os.tmpdir(), "pi-lsp-watcher-"));
+  });
+
+  after(() => {
+    fs.rmSync(tmpDir, { recursive: true, force: true });
+  });
+
+  beforeEach(async () => {
+    if (watcher) {
+      await watcher.dispose();
+      watcher = null;
+    }
+    received = [];
+    for (const entry of fs.readdirSync(tmpDir)) {
+      fs.rmSync(path.join(tmpDir, entry), { recursive: true, force: true });
+    }
+  });
+
+  it("emits Created event for new file matching pattern", async () => {
+    watcher = new WorkspaceWatcher(tmpDir, (evs) => received.push(evs));
+    watcher.setPatterns([{ globPattern: "**/*.ts" }]);
+    await watcher.ready();
+
+    fs.writeFileSync(path.join(tmpDir, "foo.ts"), "x");
+
+    const ok = await waitFor(() => received.length > 0);
+    assert.ok(ok, "Expected at least one batch");
+    const all = received.flat();
+    const match = all.find((e) => e.uri === pathToUri(path.join(tmpDir, "foo.ts")));
+    assert.ok(match, `Expected event for foo.ts, got ${JSON.stringify(all)}`);
+    assert.strictEqual(match.type, 1);
+  });
+
+  it("emits Deleted event when file removed", async () => {
+    const file = path.join(tmpDir, "del.ts");
+    fs.writeFileSync(file, "x");
+    watcher = new WorkspaceWatcher(tmpDir, (evs) => received.push(evs));
+    watcher.setPatterns([{ globPattern: "**/*.ts" }]);
+    await watcher.ready();
+
+    fs.unlinkSync(file);
+
+    const ok = await waitFor(() =>
+      received.flat().some((e) => e.type === 3 && e.uri === pathToUri(file)),
+    );
+    assert.ok(ok, `Expected delete event, got ${JSON.stringify(received)}`);
+  });
+
+  it("emits Changed event when file content changes", async () => {
+    const file = path.join(tmpDir, "chg.ts");
+    fs.writeFileSync(file, "x");
+    watcher = new WorkspaceWatcher(tmpDir, (evs) => received.push(evs));
+    watcher.setPatterns([{ globPattern: "**/*.ts" }]);
+    await watcher.ready();
+
+    fs.writeFileSync(file, "y");
+
+    const ok = await waitFor(() =>
+      received.flat().some((e) => e.type === 2 && e.uri === pathToUri(file)),
+    );
+    assert.ok(ok, `Expected change event, got ${JSON.stringify(received)}`);
+  });
+
+  it("skips files not matching the pattern", async () => {
+    watcher = new WorkspaceWatcher(tmpDir, (evs) => received.push(evs));
+    watcher.setPatterns([{ globPattern: "**/*.ts" }]);
+    await watcher.ready();
+
+    fs.writeFileSync(path.join(tmpDir, "ignored.txt"), "x");
+    await new Promise((r) => setTimeout(r, FLUSH_WAIT_MS));
+
+    const all = received.flat();
+    assert.strictEqual(
+      all.length,
+      0,
+      `Expected no events for .txt, got ${JSON.stringify(all)}`,
+    );
+  });
+
+  it("honors .gitignore at root", async () => {
+    fs.writeFileSync(path.join(tmpDir, ".gitignore"), "ignored-dir/\n");
+    fs.mkdirSync(path.join(tmpDir, "ignored-dir"));
+    watcher = new WorkspaceWatcher(tmpDir, (evs) => received.push(evs));
+    watcher.setPatterns([{ globPattern: "**/*.ts" }]);
+    await watcher.ready();
+
+    fs.writeFileSync(path.join(tmpDir, "ignored-dir", "x.ts"), "x");
+    fs.writeFileSync(path.join(tmpDir, "watched.ts"), "x");
+
+    await new Promise((r) => setTimeout(r, FLUSH_WAIT_MS));
+
+    const all = received.flat();
+    const uris = all.map((e) => e.uri);
+    assert.ok(
+      uris.includes(pathToUri(path.join(tmpDir, "watched.ts"))),
+      "watched.ts should fire",
+    );
+    assert.ok(
+      !uris.some((u) => u.includes("ignored-dir")),
+      `ignored-dir/x.ts should be filtered, got ${JSON.stringify(uris)}`,
+    );
+  });
+
+  it("respects WatchKind to filter event types", async () => {
+    watcher = new WorkspaceWatcher(tmpDir, (evs) => received.push(evs));
+    watcher.setPatterns([{ globPattern: "**/*.ts", kind: 1 }]);
+    await watcher.ready();
+
+    const file = path.join(tmpDir, "only-create.ts");
+    fs.writeFileSync(file, "x");
+    await new Promise((r) => setTimeout(r, FLUSH_WAIT_MS));
+    fs.unlinkSync(file);
+    await new Promise((r) => setTimeout(r, FLUSH_WAIT_MS));
+
+    const all = received.flat();
+    assert.ok(
+      all.some((e) => e.type === 1),
+      "Expected create event",
+    );
+    assert.ok(
+      !all.some((e) => e.type === 3),
+      `Did not expect delete events, got ${JSON.stringify(all)}`,
+    );
+  });
+
+  it("batches multiple rapid events into one onEvents call", async () => {
+    watcher = new WorkspaceWatcher(tmpDir, (evs) => received.push(evs));
+    watcher.setPatterns([{ globPattern: "**/*.ts" }]);
+    await watcher.ready();
+
+    for (let i = 0; i < 5; i++) {
+      fs.writeFileSync(path.join(tmpDir, `f${i}.ts`), "x");
+    }
+
+    await new Promise((r) => setTimeout(r, FLUSH_WAIT_MS));
+
+    const all = received.flat();
+    assert.strictEqual(all.length, 5, `Expected 5 events, got ${all.length}`);
+    assert.ok(
+      received.length <= 2,
+      `Expected <=2 batches, got ${received.length}: ${JSON.stringify(received)}`,
+    );
+  });
+
+  it("ignores .git/ even when not in gitignore", async () => {
+    watcher = new WorkspaceWatcher(tmpDir, (evs) => received.push(evs));
+    watcher.setPatterns([{ globPattern: "**/*" }]);
+    await watcher.ready();
+
+    fs.mkdirSync(path.join(tmpDir, ".git"));
+    fs.writeFileSync(path.join(tmpDir, ".git", "HEAD"), "ref: foo");
+
+    await new Promise((r) => setTimeout(r, FLUSH_WAIT_MS));
+
+    const all = received.flat();
+    assert.ok(
+      !all.some((e) => e.uri.includes("/.git/")),
+      `.git contents should be ignored, got ${JSON.stringify(all)}`,
+    );
+  });
+
+  it("stops emitting after dispose", async () => {
+    watcher = new WorkspaceWatcher(tmpDir, (evs) => received.push(evs));
+    watcher.setPatterns([{ globPattern: "**/*.ts" }]);
+    await watcher.ready();
+
+    await watcher.dispose();
+    watcher = null;
+
+    fs.writeFileSync(path.join(tmpDir, "post-dispose.ts"), "x");
+    await new Promise((r) => setTimeout(r, FLUSH_WAIT_MS));
+
+    const all = received.flat();
+    assert.strictEqual(all.length, 0, `Expected no events after dispose`);
+  });
+
+  it("matches absolute-path glob patterns (gopls-style)", async () => {
+    watcher = new WorkspaceWatcher(tmpDir, (evs) => received.push(evs));
+    watcher.setPatterns([
+      { globPattern: `${tmpDir}/**/*.{go,mod}` },
+    ]);
+    await watcher.ready();
+
+    fs.writeFileSync(path.join(tmpDir, "helper.go"), "package x\n");
+
+    const ok = await waitFor(() =>
+      received
+        .flat()
+        .some((e) => e.uri === pathToUri(path.join(tmpDir, "helper.go"))),
+    );
+    assert.ok(ok, `Expected event for absolute glob, got ${JSON.stringify(received)}`);
+  });
+
+  it("coalesces Created+Deleted to no-op", async () => {
+    watcher = new WorkspaceWatcher(tmpDir, (evs) => received.push(evs));
+    watcher.setPatterns([{ globPattern: "**/*.ts" }]);
+    await watcher.ready();
+
+    const file = path.join(tmpDir, "transient.ts");
+    fs.writeFileSync(file, "x");
+    fs.unlinkSync(file);
+
+    await new Promise((r) => setTimeout(r, FLUSH_WAIT_MS));
+
+    const all = received.flat();
+    assert.ok(
+      !all.some((e) => e.uri === pathToUri(file)),
+      `Transient file should not surface, got ${JSON.stringify(all)}`,
+    );
+  });
+
+  it("coalesces Deleted+Created (replacement) to Changed", async () => {
+    const file = path.join(tmpDir, "replace.ts");
+    fs.writeFileSync(file, "v1");
+    watcher = new WorkspaceWatcher(tmpDir, (evs) => received.push(evs));
+    watcher.setPatterns([{ globPattern: "**/*.ts" }]);
+    await watcher.ready();
+
+    fs.unlinkSync(file);
+    fs.writeFileSync(file, "v2");
+
+    await new Promise((r) => setTimeout(r, FLUSH_WAIT_MS));
+
+    const all = received.flat();
+    const events = all.filter((e) => e.uri === pathToUri(file));
+    assert.ok(events.length > 0, `Expected an event for replaced file`);
+    const types = events.map((e) => e.type).sort();
+    const acceptable =
+      JSON.stringify(types) === JSON.stringify([2]) ||
+      JSON.stringify(types) === JSON.stringify([1, 3]);
+    assert.ok(
+      acceptable,
+      `Expected [2] or [1,3], got ${JSON.stringify(types)}`,
+    );
+  });
+
+  it("drops pending events when patterns are cleared", async () => {
+    watcher = new WorkspaceWatcher(tmpDir, (evs) => received.push(evs));
+    watcher.setPatterns([{ globPattern: "**/*.ts" }]);
+    await watcher.ready();
+
+    fs.writeFileSync(path.join(tmpDir, "pending.ts"), "x");
+    await new Promise((r) => setTimeout(r, 10));
+    watcher.setPatterns([]);
+
+    await new Promise((r) => setTimeout(r, FLUSH_WAIT_MS));
+
+    assert.strictEqual(
+      received.length,
+      0,
+      `Pending batch should be dropped, got ${JSON.stringify(received)}`,
+    );
+  });
+
+  it("empty pattern set means no watching", async () => {
+    watcher = new WorkspaceWatcher(tmpDir, (evs) => received.push(evs));
+    watcher.setPatterns([]);
+    await watcher.ready();
+
+    fs.writeFileSync(path.join(tmpDir, "no-patterns.ts"), "x");
+    await new Promise((r) => setTimeout(r, FLUSH_WAIT_MS));
+
+    assert.strictEqual(received.length, 0);
+  });
+});