fix(lsp): stop per-edit hangs on dead/slow servers (10s cap + skip + self-heal)

The LSP diagnostics path hung up to 60s per edit whenever a configured Ruby
language server was dead or slow (the reported Steep langserver case): a
killed/crashed server was never detected (stayed "connected" forever), servers
were queried sequentially with a 60s budget each, and a corrupted-but-alive
server (Steep's ~3h phantom-SyntaxError drift) had no recovery.

Four fixes, all in packages/lsp/ (the tool-edit-file call site lowered to 10s):

1. Dead-process detection: SpawnedProcess.onExit (Bun proc.exited) + stdout-end
   defence flip the client to error, dispose the rpc, kill the proc. The manager
   re-spawns a fresh server after the 30s backoff. Dead servers are now skipped
   (0s) instead of polled for 60s.

2. Concurrent fan-out + 10s hard cap: new aggregateDiagnostics queries all
   matching servers at once, each capped at 10s. A non-responder is skipped
   with "LSP took too long (>10s), skipped — raise this to the user" instead of
   blocking the fast server's results. Replaces the vague "unusually long"
   warning (now structurally impossible: slow is always false).

3. Corruption self-heal: a detector flags a server re-emitting identical
   non-empty diagnostics despite the file changing; after 5 repeats the client
   is marked broken and re-spawned. Clean files never trip it. (Acknowledged
   false-positive risk on persistent unfixed errors; CLI type-check gate stays
   authoritative.)

4. sendRequest timeout: hover/definition/references cap at 10s so they can't
   hang the turn against a dead server; the initialize handshake keeps its 45s
   race.

Verification: typecheck clean; 1573 tests pass (96 files), +15 new LSP tests
(86 in packages/lsp); biome clean. No kernel/contract changes; onExit is
internal to packages/lsp.

1 files changed, 97 insertions, 0 deletions

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");
+	});
 });