fix(coding-agent/lsp): surface server exit errors and add per-server warmup timeout

Previously, any LSP server failure during initialize (process crash, missing
binary, rustup proxy error) was reported as a generic "timed out" message.
The process exit and its stderr were ignored; only the per-request timeout
fired, hiding the actual cause.

proc.exited now rejects all pending requests with the server's stderr output.
ptree already captures stderr and awaits its completion for non-zero exits,
so peekStderr() is reliable at this point. The first rejection wins the race
against the timeout; the other finds the request already removed and no-ops.

Also added warmupTimeoutMs to ServerConfig, allowing per-server override of
the global 5s warmup cap via lsp.json/lsp.yaml. Servers without it fall back
to WARMUP_TIMEOUT_MS as before.

Timeout error messages now include the configured duration for clarity when
they do legitimately fire.

packages/coding-agent/src/lsp/client.ts

@@ -436,6 +436,19 @@ export async function getOrCreateClient(config: ServerConfig, cwd: string, initT
 		proc.exited.then(() => {
 			clients.delete(key);
 			clientLocks.delete(key);
+
+			// Reject any pending requests — the server is gone, they will never complete.
+			if (client.pendingRequests.size > 0) {
+				const stderr = proc.peekStderr().trim();
+				const code = proc.exitCode;
+				const err = new Error(
+					stderr ? `LSP server exited (code ${code}): ${stderr}` : `LSP server exited unexpectedly (code ${code})`,
+				);
+				for (const pending of client.pendingRequests.values()) {
+					pending.reject(err);
+				}
+				client.pendingRequests.clear();
+			}
 		});
 
 		// Start background message reader
@@ -743,7 +756,7 @@ export async function sendRequest(
 	timeout = setTimeout(() => {
 		if (client.pendingRequests.has(id)) {
 			client.pendingRequests.delete(id);
-			const err = new Error(`LSP request ${method} timed out`);
+			const err = new Error(`LSP request ${method} timed out after ${timeoutMs}ms`);
 			cleanup();
 			reject(err);
 		}

packages/coding-agent/src/lsp/index.ts

@@ -102,7 +102,7 @@ export async function warmupLspServers(cwd: string, options?: LspWarmupOptions):
 	// Servers that don't respond quickly will be initialized lazily on first use
 	const results = await Promise.allSettled(
 		lspServers.map(async ([name, serverConfig]) => {
-			const client = await getOrCreateClient(serverConfig, cwd, WARMUP_TIMEOUT_MS);
+			const client = await getOrCreateClient(serverConfig, cwd, serverConfig.warmupTimeoutMs ?? WARMUP_TIMEOUT_MS);
 			return { name, client, fileTypes: serverConfig.fileTypes };
 		}),
 	);

packages/coding-agent/src/lsp/types.ts

@@ -358,6 +358,8 @@ export interface ServerConfig {
 	initOptions?: Record<string, unknown>;
 	settings?: Record<string, unknown>;
 	disabled?: boolean;
+	/** Per-server warmup timeout in milliseconds. Overrides the global WARMUP_TIMEOUT_MS for this server during startup. */
+	warmupTimeoutMs?: number;
 	capabilities?: ServerCapabilities;
 	/** If true, this is a linter/formatter server (e.g., Biome) - used only for diagnostics/actions, not type intelligence */
 	isLinter?: boolean;