13 files changed, 808 insertions, 69 deletions

diff --git a/packages/lsp/src/aggregate.test.ts b/packages/lsp/src/aggregate.test.ts
new file mode 100644
index 0000000..4579a0a
--- /dev/null
+++ b/packages/lsp/src/aggregate.test.ts
@@ -0,0 +1,141 @@
+import { describe, expect, it } from "vitest";
+import { type AggregateServer, aggregateDiagnostics } from "./aggregate.js";
+import type { LanguageServerClient } from "./client.js";
+
+/**
+ * A minimal fake client: only `waitForDiagnostics` is exercised by
+ * aggregateDiagnostics, so we stub just that. Cast to the real type (mirrors
+ * tool.test.ts) — no real process, no internal mocks of our own modules.
+ */
+function fakeClient(
+	waitForDiagnostics: LanguageServerClient["waitForDiagnostics"],
+): LanguageServerClient {
+	return { waitForDiagnostics } as unknown as LanguageServerClient;
+}
+
+const SERVER_A: AggregateServer = { id: "a", name: "Ruby-LSP", root: "/p" };
+const SERVER_B: AggregateServer = { id: "b", name: "Steep", root: "/p" };
+
+describe("aggregateDiagnostics", () => {
+	it("returns merged diagnostics from all responding servers, tagged by source", async () => {
+		const clients = new Map<string, LanguageServerClient>([
+			[
+				"a",
+				fakeClient(async () => ({ formatted: "ERROR L1:1: boom", slow: false, timedOut: false })),
+			],
+			[
+				"b",
+				fakeClient(async () => ({ formatted: "WARNING L2:3: meh", slow: false, timedOut: false })),
+			],
+		]);
+
+		const result = await aggregateDiagnostics(
+			(id) => clients.get(id),
+			[SERVER_A, SERVER_B],
+			"/p/x.rb",
+			10_000,
+			{},
+		);
+
+		expect(result.timedOut).toBe(false);
+		expect(result.formatted).toContain("[Ruby-LSP]");
+		expect(result.formatted).toContain("boom");
+		expect(result.formatted).toContain("[Steep]");
+		expect(result.formatted).toContain("meh");
+	});
+
+	it("skips a server that times out with a raise-to-user notice, and still returns the fast server's result", async () => {
+		// Steep never resolves within the cap → timedOut; ruby-lsp answers fast.
+		const clients = new Map<string, LanguageServerClient>([
+			["a", fakeClient(async () => ({ formatted: "", slow: false, timedOut: false }))],
+			["b", fakeClient(async () => ({ formatted: "", slow: false, timedOut: true }))],
+		]);
+
+		const result = await aggregateDiagnostics(
+			(id) => clients.get(id),
+			[SERVER_A, SERVER_B],
+			"/p/x.rb",
+			10_000,
+			{},
+		);
+
+		expect(result.timedOut).toBe(true);
+		// The skip notice names the offending server and the cap.
+		expect(result.formatted).toContain("[Steep]");
+		expect(result.formatted).toContain("took too long");
+		expect(result.formatted).toContain(">10s");
+		expect(result.formatted).toContain("raise this to the user");
+		// ruby-lsp answered cleanly (empty diagnostics) → no line for it.
+		expect(result.formatted).not.toContain("[Ruby-LSP]");
+	});
+
+	it("runs servers concurrently: a slow server does not delay a fast one's contribution order", async () => {
+		const callOrder: string[] = [];
+		const clients = new Map<string, LanguageServerClient>([
+			[
+				"a",
+				fakeClient(async () => {
+					callOrder.push("a-start");
+					await new Promise((r) => setTimeout(r, 5));
+					callOrder.push("a-end");
+					return { formatted: "from-a", slow: false, timedOut: false };
+				}),
+			],
+			[
+				"b",
+				fakeClient(async () => {
+					callOrder.push("b-start");
+					await new Promise((r) => setTimeout(r, 30));
+					callOrder.push("b-end");
+					return { formatted: "from-b", slow: false, timedOut: false };
+				}),
+			],
+		]);
+
+		const result = await aggregateDiagnostics(
+			(id) => clients.get(id),
+			[SERVER_A, SERVER_B],
+			"/p/x.rb",
+			10_000,
+			{},
+		);
+
+		// Both started before either ended → concurrent, not sequential.
+		expect(callOrder.slice(0, 2).sort()).toEqual(["a-start", "b-start"]);
+		expect(result.formatted).toContain("from-a");
+		expect(result.formatted).toContain("from-b");
+	});
+
+	it("a missing client (dead/excluded) contributes nothing and never rejects", async () => {
+		const result = await aggregateDiagnostics(() => undefined, [SERVER_A], "/p/x.rb", 10_000, {});
+		expect(result.formatted).toBe("");
+		expect(result.timedOut).toBe(false);
+	});
+
+	it("forwards text + minSeverity to each client's waitForDiagnostics", async () => {
+		const seen: Array<{ text?: string; minSeverity?: number; timeoutMs: number }> = [];
+		const clients = new Map<string, LanguageServerClient>([
+			[
+				"a",
+				fakeClient(async (_path, opts) => {
+					seen.push({
+						text: opts?.text,
+						minSeverity: opts?.minSeverity,
+						timeoutMs: opts?.timeoutMs ?? -1,
+					});
+					return { formatted: "", slow: false, timedOut: false };
+				}),
+			],
+		]);
+
+		await aggregateDiagnostics((id) => clients.get(id), [SERVER_A], "/p/x.rb", 7000, {
+			text: "post-edit buffer",
+			minSeverity: 2,
+		});
+
+		expect(seen).toHaveLength(1);
+		expect(seen[0]?.text).toBe("post-edit buffer");
+		expect(seen[0]?.minSeverity).toBe(2);
+		expect(seen[0]?.timeoutMs).toBe(7000);
+	});
+});
diff --git a/packages/lsp/src/aggregate.ts b/packages/lsp/src/aggregate.ts
new file mode 100644
index 0000000..b044e21
--- /dev/null
+++ b/packages/lsp/src/aggregate.ts
@@ -0,0 +1,80 @@
+/**
+ * Concurrent multi-server diagnostics aggregation.
+ *
+ * Queries every matching language server AT ONCE (not one-at-a-time), each
+ * capped at `timeoutMs`. A server that doesn't push diagnostics within the cap
+ * is SKIPPED with a per-server notice rather than blocking the others — so one
+ * slow/dead server (e.g. a corrupted Steep) can't hold up the fast one's
+ * (ruby-lsp) results for the full timeout on every edit.
+ *
+ * The only I/O here is `client.waitForDiagnostics` (injected via `getClient`),
+ * so this is unit-testable with a fake client and no real process.
+ */
+
+import type { LanguageServerClient } from "./client.js";
+
+export interface AggregateServer {
+	readonly id: string;
+	readonly name: string;
+	readonly root: string;
+}
+
+export interface AggregateOpts {
+	/** Post-edit buffer; when omitted the server reads from disk. */
+	readonly text?: string | undefined;
+	/** Only include diagnostics with severity ≤ this (1=Error, 2=Warning). */
+	readonly minSeverity?: number | undefined;
+}
+
+export interface AggregateResult {
+	/** Merged diagnostics tagged by source + a per-skipped-server notice. */
+	readonly formatted: string;
+	/** True if at least one server was skipped for exceeding the cap. */
+	readonly timedOut: boolean;
+}
+
+/**
+ * Query `servers` concurrently, each capped at `timeoutMs`. Returns merged
+ * diagnostics tagged by source (`[name]\n…`) and, for any server that did not
+ * respond in time, a `⚠️ [name] LSP took too long (>Ns), skipped — please raise
+ * this to the user.` notice. Never rejects: a client error yields an empty
+ * contribution for that server.
+ */
+export async function aggregateDiagnostics(
+	getClient: (id: string, root: string) => LanguageServerClient | undefined,
+	servers: readonly AggregateServer[],
+	absolutePath: string,
+	timeoutMs: number,
+	opts: AggregateOpts,
+): Promise<AggregateResult> {
+	const entries = await Promise.all(
+		servers.map(async (server) => {
+			const client = getClient(server.id, server.root);
+			if (!client) return null;
+			const waitOpts: { text?: string; timeoutMs: number; minSeverity?: number } = { timeoutMs };
+			if (opts.text !== undefined) waitOpts.text = opts.text;
+			if (opts.minSeverity !== undefined) waitOpts.minSeverity = opts.minSeverity;
+			const result = await client.waitForDiagnostics(absolutePath, waitOpts);
+			return { server, result };
+		}),
+	);
+
+	const parts: string[] = [];
+	let timedOut = false;
+	const capSeconds = Math.round(timeoutMs / 1000);
+
+	for (const entry of entries) {
+		if (!entry) continue;
+		const { server, result } = entry;
+		if (result.timedOut) {
+			timedOut = true;
+			parts.push(
+				`⚠️ [${server.name}] LSP took too long (>${capSeconds}s), diagnostics skipped — please raise this to the user.`,
+			);
+		} else if (result.formatted) {
+			parts.push(`[${server.name}]\n${result.formatted}`);
+		}
+	}
+
+	return { formatted: parts.join("\n\n"), timedOut };
+}
diff --git a/packages/lsp/src/client.test.ts b/packages/lsp/src/client.test.ts
index 681860f..338ef0b 100644
--- a/packages/lsp/src/client.test.ts
+++ b/packages/lsp/src/client.test.ts
@@ -3,6 +3,7 @@ import {
 	type FileWatcher,
 	type FsAccess,
 	LanguageServerClient,
+	type ProcessExitHandler,
 	type SpawnProcess,
 } from "./client.js";
 import { encode } from "./framing.js";
@@ -288,4 +289,149 @@ describe("client", () => {
 		client.shutdown();
 		expect(state.killed).toBe(true);
 	});
+
+	it("onExit marks the client broken (error) so callers stop querying a corpse", async () => {
+		const state = { killed: false };
+		let exitCb: ProcessExitHandler | null = null;
+		const stdoutHolder: { cb: ((data: Uint8Array) => void) | null } = { cb: null };
+
+		const spawnWithExit: SpawnProcess = () => ({
+			stdin: { write: () => {} },
+			stdout: {
+				on: (_event: string, cb: (data: Uint8Array) => void) => {
+					stdoutHolder.cb = cb;
+				},
+			},
+			pid: 999,
+			kill: () => {
+				state.killed = true;
+			},
+			onExit: (handler) => {
+				exitCb = handler;
+			},
+		});
+
+		const { client } = makeClient({ spawn: spawnWithExit });
+		const startPromise = client.start();
+		await new Promise((r) => setTimeout(r, 50));
+		stdoutHolder.cb?.(
+			encode(JSON.stringify({ jsonrpc: "2.0", id: 1, result: { capabilities: {} } })),
+		);
+		await startPromise;
+		expect(client.getState()).toBe("connected");
+
+		// Simulate the process dying (user kill / crash).
+		exitCb?.({ code: 1 });
+
+		expect(client.getState()).toBe("error");
+		expect(client.getStateError()).toMatch(/process exited/);
+		// The (still-alive-in-test) process was killed to avoid a zombie.
+		expect(state.killed).toBe(true);
+	});
+
+	it("a dead client is skipped by waitForDiagnostics callers (state !== connected)", async () => {
+		// Build a client, connect, kill via onExit, then assert a diagnostics
+		// query would not block: getState() is "error" so the matching filter
+		// (state === "connected") excludes it. We assert the state guard.
+		const stdoutHolder: { cb: ((data: Uint8Array) => void) | null } = { cb: null };
+		let exitCb: ProcessExitHandler | null = null;
+		const spawnWithExit: SpawnProcess = () => ({
+			stdin: { write: () => {} },
+			stdout: {
+				on: (_e, cb) => {
+					stdoutHolder.cb = cb;
+				},
+			},
+			pid: 1,
+			kill: () => {},
+			onExit: (handler) => {
+				exitCb = handler;
+			},
+		});
+
+		const { client } = makeClient({ spawn: spawnWithExit });
+		const startPromise = client.start();
+		await new Promise((r) => setTimeout(r, 50));
+		stdoutHolder.cb?.(
+			encode(JSON.stringify({ jsonrpc: "2.0", id: 1, result: { capabilities: {} } })),
+		);
+		await startPromise;
+
+		exitCb?.({ code: null });
+		expect(client.getState()).toBe("error");
+		// The aggregate / getDiagnostics matching filter requires "connected".
+		expect(client.getState() === "connected").toBe(false);
+	});
+
+	it("corruption detector marks the client broken after repeated identical diagnostics despite text changes", async () => {
+		// A healthy server would change diagnostics as the file changes; a
+		// corrupted one re-emits the SAME non-empty set. Drive 5 edits with
+		// different text but identical diagnostics → client flips to error.
+		const { client, serverResponses } = makeClient();
+		const startPromise = client.start();
+		await new Promise((r) => setTimeout(r, 50));
+		serverResponses(JSON.stringify({ jsonrpc: "2.0", id: 1, result: { capabilities: {} } }));
+		await startPromise;
+
+		const phantom = JSON.stringify({
+			jsonrpc: "2.0",
+			method: "textDocument/publishDiagnostics",
+			params: {
+				uri: "file:///project/game.rb",
+				diagnostics: [
+					{
+						range: { start: { line: 0, character: 27 }, end: { line: 0, character: 28 } },
+						severity: 1,
+						message: "SyntaxError: unexpected token",
+					},
+				],
+			},
+		});
+
+		const path = "/project/game.rb";
+		// The first call establishes the baseline snapshot (no increment).
+		// Each subsequent call with identical diagnostics + changed text
+		// increments; the 6th call (5th increment) trips the threshold.
+		for (let i = 1; i <= 5; i++) {
+			const p = client.waitForDiagnostics(path, { text: `buf-v${i}`, timeoutMs: 2000 });
+			// Push the identical phantom diagnostics so the poll resolves.
+			await new Promise((r) => setTimeout(r, 30));
+			serverResponses(phantom);
+			await p;
+			expect(client.getState()).toBe("connected");
+		}
+		// 6th identical-across-changed-text repeat trips the threshold.
+		const p6 = client.waitForDiagnostics(path, { text: "buf-v6", timeoutMs: 2000 });
+		await new Promise((r) => setTimeout(r, 30));
+		serverResponses(phantom);
+		await p6;
+
+		expect(client.getState()).toBe("error");
+		expect(client.getStateError()).toMatch(/repeated stale diagnostics/i);
+	});
+
+	it("corruption detector does NOT trip on a clean file (empty diagnostics stay identical)", async () => {
+		const { client, serverResponses } = makeClient();
+		const startPromise = client.start();
+		await new Promise((r) => setTimeout(r, 50));
+		serverResponses(JSON.stringify({ jsonrpc: "2.0", id: 1, result: { capabilities: {} } }));
+		await startPromise;
+
+		const clean = JSON.stringify({
+			jsonrpc: "2.0",
+			method: "textDocument/publishDiagnostics",
+			params: { uri: "file:///project/game.rb", diagnostics: [] },
+		});
+		const path = "/project/game.rb";
+
+		for (let i = 1; i <= 6; i++) {
+			const p = client.waitForDiagnostics(path, { text: `clean-v${i}`, timeoutMs: 2000 });
+			await new Promise((r) => setTimeout(r, 30));
+			serverResponses(clean);
+			await p;
+		}
+		// Empty diagnostics never count as "stale" — a clean file staying clean
+		// is normal, not corruption.
+		expect(client.getState()).toBe("connected");
+	});
 });
diff --git a/packages/lsp/src/client.ts b/packages/lsp/src/client.ts
index 677a22a..ac7d025 100644
--- a/packages/lsp/src/client.ts
+++ b/packages/lsp/src/client.ts
@@ -4,13 +4,22 @@
  * FileWatcher, and forwards matching disk changes.
  */
 
-import { DiagnosticsStore, type PublishDiagnosticsParams } from "./diagnostics.js";
+import { DiagnosticsStore, diagnosticKey, type PublishDiagnosticsParams } from "./diagnostics.js";
 import { computeChangeRange } from "./diff.js";
 import { FrameDecoder } from "./framing.js";
 import { languageId as resolveLanguageId } from "./language.js";
 import { JsonRpcConnection, type WriteFn } from "./rpc.js";
 import { FileChangeType, WatchedFilesRegistry } from "./watched-files.js";
 
+/** Info delivered to an `onExit` handler when the child process terminates. */
+export interface ProcessExitInfo {
+	readonly code: number | null;
+	readonly signal?: string;
+}
+
+/** A handler registered to be called when the child process exits. */
+export type ProcessExitHandler = (info: ProcessExitInfo) => void;
+
 export interface SpawnedProcess {
 	readonly stdin: { readonly write: (bytes: Uint8Array) => void };
 	readonly stdout:
@@ -22,6 +31,13 @@ export interface SpawnedProcess {
 		| undefined;
 	readonly pid: number | undefined;
 	readonly kill: () => void;
+	/**
+	 * Register a handler fired when the child process exits (code|signal).
+	 * Optional: when absent, death is detected via stdout-end instead. Wires
+	 * Bun's `proc.exited` in production; tests invoke it directly to simulate
+	 * a crash. Lets the client stop querying a dead server (no per-edit hang).
+	 */
+	readonly onExit?: ((handler: ProcessExitHandler) => void) | undefined;
 }
 
 export type SpawnProcess = (
@@ -102,6 +118,18 @@ export class LanguageServerClient {
 	private openDocuments = new Map<string, { version: number; text: string }>();
 	/** Sync mode captured from the server's initialize capabilities: 1=Full, 2=Incremental. */
 	private textDocumentChange: 1 | 2 = 1;
+	/**
+	 * Corruption detection: the last diagnostic-key set + synced text per URI.
+	 * A healthy server's diagnostics change when the file changes; a corrupted
+	 * one (e.g. Steep's ~3h phantom-SyntaxError drift) re-emits the identical
+	 * non-empty set across edits. `staleRepeat` counts consecutive such repeats
+	 * across URIs; at the threshold the client is marked broken (→ respawn).
+	 */
+	private lastDiagSnapshot = new Map<string, { keys: Set<string>; text: string }>();
+	private staleRepeat = 0;
+	private static readonly STALE_REPEAT_THRESHOLD = 5;
+	/** Default timeout for outbound requests (hover/definition/references). */
+	private static readonly REQUEST_TIMEOUT_MS = 10_000;
 
 	constructor(deps: ClientDeps) {
 		this.deps = deps;
@@ -128,6 +156,12 @@ export class LanguageServerClient {
 			}
 			const proc = this.deps.spawn(this.deps.command as string[], spawnOpts);
 			this.process = proc;
+			// Detect process death so we stop querying a corpse (fixes the
+			// per-edit hang after a server is killed/crashes). onExit is the
+			// primary signal; stdout-end is the defence-in-depth fallback.
+			if (proc.onExit) {
+				proc.onExit((info) => this.handleExit(info));
+			}
 
 			const writeFn: WriteFn = (bytes) => proc.stdin.write(bytes);
 			const rpc = new JsonRpcConnection(writeFn);
@@ -158,8 +192,11 @@ export class LanguageServerClient {
 				for await (const chunk of source) {
 					this.handleBytes(chunk);
 				}
+				// stdout closed — the process is gone (defence-in-depth alongside onExit,
+				// which some edges never call). Idempotent via handleExit's guard.
+				this.handleExit({ code: null });
 			} catch {
-				// process exited
+				this.handleExit({ code: null });
 			}
 		})();
 	}
@@ -172,6 +209,65 @@ export class LanguageServerClient {
 		});
 	}
 
+	/**
+	 * The server process exited (onExit or stdout-end). Transition to a broken
+	 * state so callers skip it and the manager re-spawns after backoff — instead
+	 * of polling a corpse for the full timeout on every edit. Idempotent.
+	 */
+	private handleExit(info: ProcessExitInfo): void {
+		if (this.state === "error" || this.state === "not-started") return;
+		const detail = info.signal !== undefined ? `signal ${info.signal}` : `code ${info.code ?? "?"}`;
+		this.markBroken(`language server process exited (${detail})`);
+	}
+
+	/**
+	 * Mark this client permanently broken: kill the process if still alive
+	 * (corruption case), dispose the rpc (rejects pending requests), and drop
+	 * edge handles. The manager's status() observes state:"error" and re-spawns
+	 * after the bounded backoff. Called on process death AND on corruption.
+	 */
+	private markBroken(reason: string): void {
+		if (this.state === "error") return;
+		this.state = "error";
+		this.stateError = reason;
+		this.fileWatcherHandle?.close();
+		this.fileWatcherHandle = null;
+		this.process?.kill();
+		this.process = null;
+		this.rpc?.dispose();
+		this.rpc = null;
+	}
+
+	/**
+	 * Detect a server stuck re-emitting identical non-empty diagnostics
+	 * despite the file content changing between calls — the signature of a
+	 * corrupted parse/type-check state (e.g. Steep's ~3h phantom-SyntaxError
+	 * drift, where a fresh CLI reports green on the same project). After
+	 * STALE_REPEAT_THRESHOLD consecutive such repeats, mark the client broken
+	 * so it is skipped + re-spawned. A clean file (empty diagnostics) or a
+	 * genuinely changing diagnostic set resets the counter. Note the
+	 * tradeoff: a real, unfixed error on an untouched line also "stays the
+	 * same across edits", so this can false-positive on a healthy server —
+	 * the threshold is set conservatively and the CLI type-check gate remains
+	 * authoritative either way.
+	 */
+	private detectStaleDiagnostics(uri: string, text: string): void {
+		const merged = this.diagnostics.getMerged(uri);
+		const keys = new Set(merged.map((d) => diagnosticKey(d)));
+		const prev = this.lastDiagSnapshot.get(uri);
+		if (prev && keys.size > 0 && setsEqual(keys, prev.keys) && text !== prev.text) {
+			this.staleRepeat++;
+		} else {
+			this.staleRepeat = 0;
+		}
+		this.lastDiagSnapshot.set(uri, { keys, text });
+		if (this.staleRepeat >= LanguageServerClient.STALE_REPEAT_THRESHOLD) {
+			this.markBroken(
+				"language server emitting repeated stale diagnostics despite file changes — likely corrupted; restarting",
+			);
+		}
+	}
+
 	private handleBytes(chunk: Uint8Array): void {
 		const messages = this.decoder.decode(chunk);
 		for (const msg of messages) {
@@ -403,26 +499,37 @@ export class LanguageServerClient {
 			await this.open(filePath);
 		}
 
-		const slowThreshold = 10_000;
 		const start = Date.now();
 
-		// Poll until the server pushes diagnostics (even empty = done) or timeout.
-		return new Promise((resolve) => {
+		// Poll until the server pushes diagnostics (even empty = done) or the
+		// per-server cap elapses (then we skip it — see aggregateDiagnostics).
+		const received = await new Promise<boolean>((resolve) => {
 			const check = () => {
 				const elapsed = Date.now() - start;
-				const received = this.diagnostics.hasReceivedPush(uri);
-				if (received || elapsed >= timeoutMs) {
-					resolve({
-						formatted: this.diagnostics.formatFiltered(uri, opts?.minSeverity),
-						slow: elapsed > slowThreshold,
-						timedOut: !received,
-					});
+				const got = this.diagnostics.hasReceivedPush(uri);
+				if (got || elapsed >= timeoutMs) {
+					resolve(got);
 					return;
 				}
 				setTimeout(check, 100);
 			};
 			check();
 		});
+
+		// Only a server that actually pushed can be corruption-checked.
+		if (received) {
+			this.detectStaleDiagnostics(uri, opts?.text ?? "");
+		}
+
+		// `slow` is structurally false now: the per-server cap is 10s, so
+		// elapsed can never exceed the old "unusually long" threshold. That
+		// warning is superseded by the timeout→skip notice produced in
+		// aggregateDiagnostics. The field is kept for contract compatibility.
+		return {
+			formatted: this.diagnostics.formatFiltered(uri, opts?.minSeverity),
+			slow: false,
+			timedOut: !received,
+		};
 	}
 
 	getWatchedFilesRegistry(): WatchedFilesRegistry {
@@ -433,11 +540,21 @@ export class LanguageServerClient {
 		return this.diagnostics;
 	}
 
-	async request(method: string, params?: unknown): Promise<unknown> {
+	/**
+	 * Send a request (hover/definition/references/documentSymbol). Capped at
+	 * REQUEST_TIMEOUT_MS so a dead/slow server can't hang the turn — the
+	 * initialize handshake bypasses this (it calls rpc.sendRequest directly
+	 * with its own 45s race).
+	 */
+	async request(
+		method: string,
+		params?: unknown,
+		timeoutMs: number = LanguageServerClient.REQUEST_TIMEOUT_MS,
+	): Promise<unknown> {
 		if (!this.rpc || this.state !== "connected") {
 			throw new Error("Client not connected");
 		}
-		return this.rpc.sendRequest(method, params);
+		return this.rpc.sendRequest(method, params, timeoutMs);
 	}
 
 	shutdown(): void {
@@ -450,3 +567,11 @@ export class LanguageServerClient {
 		this.state = "not-started";
 	}
 }
+
+function setsEqual<T>(a: Set<T>, b: Set<T>): boolean {
+	if (a.size !== b.size) return false;
+	for (const v of a) {
+		if (!b.has(v)) return false;
+	}
+	return true;
+}
diff --git a/packages/lsp/src/diagnostics.ts b/packages/lsp/src/diagnostics.ts
index bc7ac0a..50beca9 100644
--- a/packages/lsp/src/diagnostics.ts
+++ b/packages/lsp/src/diagnostics.ts
@@ -91,7 +91,7 @@ export class DiagnosticsStore {
 	}
 }
 
-function diagnosticKey(d: Diagnostic): string {
+export function diagnosticKey(d: Diagnostic): string {
 	const r = d.range;
 	return `${r.start.line}:${r.start.character}-${r.end.line}:${r.end.character}:${d.severity ?? 0}:${d.message}`;
 }
diff --git a/packages/lsp/src/extension.ts b/packages/lsp/src/extension.ts
index 8e3178a..c0fee44 100644
--- a/packages/lsp/src/extension.ts
+++ b/packages/lsp/src/extension.ts
@@ -8,6 +8,7 @@
 import { extname, join } from "node:path";
 import type { Extension, HostAPI, ServiceHandle } from "@dispatch/kernel";
 import { defineService } from "@dispatch/kernel";
+import { aggregateDiagnostics } from "./aggregate.js";
 import type { SpawnedProcess } from "./client.js";
 import { LspManager } from "./manager.js";
 import { createLspTool } from "./tool.js";
@@ -43,6 +44,14 @@ function realSpawn(
 		stderr: proc.stderr,
 		pid: proc.pid,
 		kill: () => proc.kill(),
+		// Surface process exit so the client can stop querying a dead server
+		// and self-heal (respawn). Bun's Subprocess.exited resolves with the
+		// exit code (or rejects if killed by signal — treat as code:null).
+		onExit: (handler) => {
+			(proc as { exited: Promise<number | null> }).exited
+				.then((code) => handler({ code }))
+				.catch(() => handler({ code: null }));
+		},
 	};
 }
 
@@ -108,14 +117,20 @@ export const extension: Extension = {
 				return manager.status(cwd);
 			},
 			async getDiagnostics(opts: GetDiagnosticsOpts): Promise<DiagnosticsResult> {
-				const timeoutMs = opts.timeoutMs ?? 60_000;
-				const slowThreshold = 10_000;
+				// 10s hard ceiling per server, regardless of what the caller
+				// passes (the edit hook still passes 60_000 — clamped here, so
+				// no other-unit edit is needed). A server that doesn't respond
+				// in 10s is skipped with a notice instead of waited out.
+				const PER_SERVER_CAP_MS = 10_000;
+				const timeoutMs = Math.min(opts.timeoutMs ?? PER_SERVER_CAP_MS, PER_SERVER_CAP_MS);
 				const fileExt = extname(opts.filePath).toLowerCase();
 				const absolutePath = opts.filePath.startsWith("/")
 					? opts.filePath
 					: join(opts.cwd, opts.filePath);
 
 				// Get all connected servers matching this file's extension.
+				// A dead/corrupted server has state:"error" and is excluded —
+				// no per-edit hang on a corpse.
 				const statuses = await manager.status(opts.cwd);
 				const matching = statuses.filter(
 					(s) => s.state === "connected" && s.extensions.some((ext) => ext === fileExt),
@@ -125,34 +140,15 @@ export const extension: Extension = {
 					return { formatted: "", slow: false, timedOut: false };
 				}
 
-				const parts: string[] = [];
-				let anySlow = false;
-				let anyTimedOut = false;
-				const start = Date.now();
-
-				for (const s of matching) {
-					const client = manager.getClient(s.id, s.root);
-					if (!client) continue;
-					const waitOpts: { text?: string; timeoutMs?: number; minSeverity?: number } = {
-						timeoutMs,
-					};
-					if (opts.text !== undefined) waitOpts.text = opts.text;
-					if (opts.minSeverity !== undefined) waitOpts.minSeverity = opts.minSeverity;
-					const result = await client.waitForDiagnostics(absolutePath, waitOpts);
-					if (result.slow) anySlow = true;
-					if (result.timedOut) anyTimedOut = true;
-					if (result.formatted) {
-						parts.push(`[${s.name}]\n${result.formatted}`);
-					}
-				}
-
-				const elapsed = Date.now() - start;
+				const agg = await aggregateDiagnostics(
+					(id, root) => manager.getClient(id, root),
+					matching,
+					absolutePath,
+					timeoutMs,
+					{ text: opts.text, minSeverity: opts.minSeverity },
+				);
 
-				return {
-					formatted: parts.join("\n\n"),
-					slow: anySlow || elapsed > slowThreshold,
-					timedOut: anyTimedOut,
-				};
+				return { formatted: agg.formatted, slow: false, timedOut: agg.timedOut };
 			},
 		};
 		host.provideService(lspServiceHandle, service);
diff --git a/packages/lsp/src/manager.test.ts b/packages/lsp/src/manager.test.ts
index 1649111..d8cba4f 100644
--- a/packages/lsp/src/manager.test.ts
+++ b/packages/lsp/src/manager.test.ts
@@ -361,4 +361,92 @@ describe("manager", () => {
 		expect(s[0]?.error).toContain("[from .dispatch/lsp.json]");
 		expect(s[0]?.error).toContain("spawn failed");
 	});
+
+	it("a client that dies after connecting is skipped + re-spawned after backoff (no storm, no eternal hang)", async () => {
+		// A spawn that completes the initialize handshake AND lets the test
+		// simulate process death via the captured onExit handler.
+		const exitHandlers: Array<(info: { code: number | null; signal?: string }) => void> = [];
+		let spawnCount = 0;
+		const spawn: SpawnProcess = () => {
+			spawnCount++;
+			let messageHandler: ((data: Uint8Array) => void) | null = null;
+			const proc: SpawnedProcess = {
+				stdin: {
+					write: (bytes: Uint8Array) => {
+						const decoded = new TextDecoder().decode(bytes);
+						const headerEnd = decoded.indexOf("\r\n\r\n");
+						if (headerEnd === -1) return;
+						const json = decoded.slice(headerEnd + 4);
+						try {
+							const msg = JSON.parse(json);
+							if (msg.method === "initialize") {
+								setTimeout(() => {
+									const response = JSON.stringify({
+										jsonrpc: "2.0",
+										id: msg.id,
+										result: { capabilities: {} },
+									});
+									messageHandler?.(encode(response));
+								}, 1);
+							}
+						} catch {
+							// ignore
+						}
+					},
+				},
+				stdout: {
+					on: (_event: string, cb: (data: Uint8Array) => void) => {
+						messageHandler = cb;
+					},
+				},
+				pid: 1000 + spawnCount,
+				kill: () => {},
+				onExit: (handler) => {
+					exitHandlers.push(handler);
+				},
+			};
+			return proc;
+		};
+
+		const clock = { now: 0 };
+		const manager = new LspManager({
+			spawn,
+			fileWatcher: noopFileWatcher(),
+			fs: fakeFs({
+				"/project/.dispatch/lsp.json": JSON.stringify({
+					servers: {
+						steep: {
+							command: ["steep", "--stdio"],
+							extensions: [".rb"],
+							rootMarkers: [],
+						},
+					},
+				}),
+			}),
+			now: () => clock.now,
+		});
+
+		// 1) Connects.
+		const s1 = await manager.status("/project");
+		expect(s1[0]?.state).toBe("connected");
+		expect(spawnCount).toBe(1);
+
+		// 2) Simulate the process dying (user kill / crash) via onExit.
+		exitHandlers[0]?.({ code: 1 });
+		const clientAfterDeath = manager.getClient("steep", "/project");
+		expect(clientAfterDeath?.getState()).toBe("error");
+
+		// 3) status() now reports error (and seeds a broken entry for backoff).
+		//    Backoff not elapsed yet (clock frozen at 0) → NOT re-spawned.
+		const s2 = await manager.status("/project");
+		expect(s2[0]?.state).toBe("error");
+		expect(s2[0]?.error).toMatch(/process exited/);
+		expect(spawnCount).toBe(1); // no retry storm before backoff
+
+		// 4) After the backoff elapses, status() re-spawns a fresh server.
+		clock.now = 31_000;
+		const s3 = await manager.status("/project");
+		expect(s3[0]?.state).toBe("connected");
+		expect(spawnCount).toBe(2); // re-spawned exactly once
+	});
 });
diff --git a/packages/lsp/src/manager.ts b/packages/lsp/src/manager.ts
index 7153956..bc84479 100644
--- a/packages/lsp/src/manager.ts
+++ b/packages/lsp/src/manager.ts
@@ -134,6 +134,19 @@ export class LspManager {
 			if (existing) {
 				const state = existing.client.getState();
 				const stateError = existing.client.getStateError();
+				// A client that died or corrupted AFTER connecting flipped its
+				// own state to "error" (client.ts handleExit/markBroken). Spawn
+				// succeeded so there's no broken entry yet — seed one so the
+				// bounded-backoff path above re-spawns it, instead of reporting
+				// error forever (and so getDiagnostics' "connected" filter skips
+				// it, avoiding a per-edit hang on the corpse).
+				if (state === "error" && !this.broken.has(key)) {
+					this.broken.set(key, {
+						configFingerprint: configFingerprint(server),
+						brokenAt: this.now(),
+						error: enrichError(server, stateError ?? "server unavailable"),
+					});
+				}
 				const status: LspServerStatus = {
 					id: server.id,
 					name: server.name,
diff --git a/packages/lsp/src/rpc.test.ts b/packages/lsp/src/rpc.test.ts
index 05ce924..7b22ec5 100644
--- a/packages/lsp/src/rpc.test.ts
+++ b/packages/lsp/src/rpc.test.ts
@@ -84,3 +84,29 @@ it("handleMessage does not throw on malformed JSON", async () => {
 	await expect(conn.handleMessage("")).resolves.toBeUndefined();
 	await expect(conn.handleMessage("not json at all")).resolves.toBeUndefined();
 });
+
+describe("sendRequest timeout", () => {
+	it("rejects with a timeout error when no response arrives within timeoutMs", async () => {
+		const { conn } = makeConnection();
+		const promise = conn.sendRequest("textDocument/hover", {}, 50);
+		await expect(promise).rejects.toThrow(/LSP request timed out after 50ms: textDocument\/hover/);
+	});
+
+	it("clears the timer on a normal response (no unhandled rejection)", async () => {
+		const { conn } = makeConnection();
+		const promise = conn.sendRequest("textDocument/hover", {}, 5000);
+		conn.handleMessage(frameResponse(1, { ok: true }));
+		await expect(promise).resolves.toEqual({ ok: true });
+		// Give the (now-cleared) timer window ample time to prove it never fires.
+		await new Promise((r) => setTimeout(r, 80));
+	});
+
+	it("does not time out when no timeoutMs is given (initialize handshake path)", async () => {
+		const { conn } = makeConnection();
+		const promise = conn.sendRequest("initialize", {});
+		// A late response well past any plausible default still resolves.
+		await new Promise((r) => setTimeout(r, 60));
+		conn.handleMessage(frameResponse(1, { capabilities: {} }));
+		await expect(promise).resolves.toEqual({ capabilities: {} });
+	});
+});
diff --git a/packages/lsp/src/rpc.ts b/packages/lsp/src/rpc.ts
index 6b82624..95157de 100644
--- a/packages/lsp/src/rpc.ts
+++ b/packages/lsp/src/rpc.ts
@@ -39,11 +39,36 @@ export class JsonRpcConnection {
 		this.write = write;
 	}
 
-	sendRequest(method: string, params?: unknown): Promise<unknown> {
+	/**
+	 * Send a request and await the correlated response. If `timeoutMs` is given,
+	 * the promise rejects with a timeout error after that long — so a dead/slow
+	 * server can't hang the caller forever (hover/definition/references).
+	 * No `timeoutMs` = wait indefinitely (used by the initialize handshake, which
+	 * has its own 45s race).
+	 */
+	sendRequest(method: string, params?: unknown, timeoutMs?: number): Promise<unknown> {
 		const id = this.nextId++;
 		const msg: JsonRpcMessage = { jsonrpc: "2.0", id, method, params };
 		return new Promise((resolve, reject) => {
-			this.pending.set(id, { resolve, reject });
+			let timer: ReturnType<typeof setTimeout> | undefined;
+			// Wrap resolve/reject so the timer is cleared on a normal response
+			// (or on dispose) — no dangling timer after completion.
+			const finish = (fn: () => void): void => {
+				if (timer) clearTimeout(timer);
+				fn();
+			};
+			const entry: PendingRequest = {
+				resolve: (value: unknown) => finish(() => resolve(value)),
+				reject: (reason: unknown) => finish(() => reject(reason)),
+			};
+			if (timeoutMs !== undefined) {
+				timer = setTimeout(() => {
+					if (this.pending.delete(id)) {
+						reject(new Error(`LSP request timed out after ${timeoutMs}ms: ${method}`));
+					}
+				}, timeoutMs);
+			}
+			this.pending.set(id, entry);
 			this.sendMessage(msg);
 		});
 	}
diff --git a/packages/lsp/src/tool.test.ts b/packages/lsp/src/tool.test.ts
index 03787ae..efd1514 100644
--- a/packages/lsp/src/tool.test.ts
+++ b/packages/lsp/src/tool.test.ts
@@ -176,4 +176,101 @@ describe("tool", () => {
 		expect(result.isError).toBe(true);
 		expect(result.content).toContain("requires both");
 	});
+
+	it("diagnostics op: a server that times out is skipped with a raise-to-user notice", async () => {
+		const mockClient = {
+			getState: () => "connected" as const,
+			getStateError: () => undefined,
+			request: async () => null,
+			waitForDiagnostics: async () => ({ formatted: "", slow: false, timedOut: true }),
+		};
+
+		const tool = createLspTool(
+			stubManager({
+				status: async () => [
+					{
+						id: "steep",
+						name: "Steep",
+						root: "/project",
+						extensions: [".rb"],
+						state: "connected",
+					},
+				],
+				getClient: () => mockClient as never,
+			}),
+		);
+
+		const result = await tool.execute(
+			{ operation: "diagnostics", path: "game.rb" },
+			{
+				toolCallId: "test",
+				onOutput: () => {},
+				signal: AbortSignal.timeout(5000),
+				log: {
+					debug: () => {},
+					info: () => {},
+					warn: () => {},
+					error: () => {},
+					child: () => ({}) as never,
+					span: () => ({}) as never,
+				},
+				cwd: "/project",
+			},
+		);
+
+		expect(result.isError).not.toBe(true);
+		expect(result.content).toContain("[Steep]");
+		expect(result.content).toContain("took too long");
+		expect(result.content).toContain(">10s");
+		expect(result.content).toContain("raise this to the user");
+	});
+
+	it("diagnostics op: responding servers' diagnostics are merged, tagged by source", async () => {
+		const mockClient = {
+			getState: () => "connected" as const,
+			getStateError: () => undefined,
+			request: async () => null,
+			waitForDiagnostics: async () => ({
+				formatted: "ERROR L1:1: boom",
+				slow: false,
+				timedOut: false,
+			}),
+		};
+
+		const tool = createLspTool(
+			stubManager({
+				status: async () => [
+					{
+						id: "steep",
+						name: "Steep",
+						root: "/project",
+						extensions: [".rb"],
+						state: "connected",
+					},
+				],
+				getClient: () => mockClient as never,
+			}),
+		);
+
+		const result = await tool.execute(
+			{ operation: "diagnostics", path: "game.rb" },
+			{
+				toolCallId: "test",
+				onOutput: () => {},
+				signal: AbortSignal.timeout(5000),
+				log: {
+					debug: () => {},
+					info: () => {},
+					warn: () => {},
+					error: () => {},
+					child: () => ({}) as never,
+					span: () => ({}) as never,
+				},
+				cwd: "/project",
+			},
+		);
+
+		expect(result.content).toContain("[Steep]");
+		expect(result.content).toContain("boom");
+	});
 });
diff --git a/packages/lsp/src/tool.ts b/packages/lsp/src/tool.ts
index 8d282ec..be0d269 100644
--- a/packages/lsp/src/tool.ts
+++ b/packages/lsp/src/tool.ts
@@ -6,6 +6,7 @@
 
 import { extname, resolve } from "node:path";
 import type { ToolContract, ToolExecuteContext, ToolResult } from "@dispatch/kernel";
+import { aggregateDiagnostics } from "./aggregate.js";
 import type { LspManager } from "./manager.js";
 
 type Operation = "diagnostics" | "hover" | "definition" | "references" | "documentSymbol";
@@ -157,6 +158,8 @@ export function createLspTool(manager: LspManager): ToolContract {
 
 				switch (operation) {
 					case "diagnostics": {
+						// 10s hard ceiling per server (same policy as the edit path).
+						const DIAGNOSTICS_TIMEOUT_MS = 10_000;
 						// Query ALL connected servers whose extensions match this file.
 						const matching = statuses.filter(
 							(s) => s.state === "connected" && s.extensions.some((ext) => ext === fileExt),
@@ -179,31 +182,27 @@ export function createLspTool(manager: LspManager): ToolContract {
 							if (!client) {
 								return { content: "Language server client not available.", isError: true };
 							}
-							const result = await client.waitForDiagnostics(absolutePath);
+							const result = await client.waitForDiagnostics(absolutePath, {
+								timeoutMs: DIAGNOSTICS_TIMEOUT_MS,
+							});
+							if (result.timedOut) {
+								return {
+									content: `⚠️ [${connected.name}] LSP took too long (>10s), diagnostics skipped — please raise this to the user.`,
+								};
+							}
 							return { content: result.formatted || "No diagnostics found." };
 						}
 
-						// Query each matching server and merge results, tagged by source.
-						const parts: string[] = [];
-						let anyTimedOut = false;
-						for (const s of matching) {
-							const client = manager.getClient(s.id, s.root);
-							if (!client) continue;
-							const result = await client.waitForDiagnostics(absolutePath, { timeoutMs: 60_000 });
-							if (result.timedOut) anyTimedOut = true;
-							if (result.slow) {
-								parts.push(
-									`⚠️ LSP is taking unusually long. If this happens more than once, raise it to the user.`,
-								);
-							}
-							if (result.formatted) {
-								parts.push(`[${s.name}]\n${result.formatted}`);
-							}
-						}
-						if (anyTimedOut && parts.length === 0) {
-							parts.push("Diagnostics timed out (server may still be indexing).");
-						}
-						return { content: parts.length > 0 ? parts.join("\n\n") : "No diagnostics found." };
+						// Query matching servers concurrently, each capped at 10s;
+						// a non-responding server is skipped with a notice.
+						const agg = await aggregateDiagnostics(
+							(id, root) => manager.getClient(id, root),
+							matching,
+							absolutePath,
+							DIAGNOSTICS_TIMEOUT_MS,
+							{},
+						);
+						return { content: agg.formatted || "No diagnostics found." };
 					}
 					case "hover": {
 						const client = await getFirstMatchingClient(manager, statuses, fileExt);
diff --git a/packages/tool-edit-file/src/extension.ts b/packages/tool-edit-file/src/extension.ts
index 3929634..2a58fac 100644
--- a/packages/tool-edit-file/src/extension.ts
+++ b/packages/tool-edit-file/src/extension.ts
@@ -33,7 +33,10 @@ export const extension: Extension = {
 				filePath: opts.filePath,
 				text: opts.text,
 				cwd: opts.cwd,
-				timeoutMs: 60_000,
+				// 10s matches the LSP service's per-server cap (see packages/lsp).
+				// The service clamps this anyway; stated explicitly so the call
+				// site is honest about the effective live-diagnostics budget.
+				timeoutMs: 10_000,
 				minSeverity: 2, // errors + warnings only
 			});
 		};