fix: throw resourceNotFound when loadSession fails to resume (#363)

## Summary

- When `loadSession` calls `createSession({ resume: sessionId })` and
the CLI subprocess can't find persisted session data (no `.jsonl` file),
the subprocess exits immediately and `createSession` rejects with a
generic `-32603` ("Query closed before response received")
- ACP clients like [acpx](https://github.com/openclaw/acpx) check for
`-32001`/`-32002` (resource not found) to fall back to `session/new` —
the generic `-32603` bypasses this, causing the turn to fail entirely
- This commonly happens when `session/new` creates an ACP session but
the subprocess exits before writing session data (no prompt to process),
then `session/prompt` tries `session/load` to resume a session that was
never persisted

## Fix

Wrap the `createSession({ resume })` call in `loadSession()` with
try/catch and re-throw as `RequestError.resourceNotFound()` (code
`-32002`). This lets callers handle it with their existing fallback
logic.

## Verification

Confirmed working in production with the
[OpenClaw](https://github.com/openclaw/openclaw) gateway + acpx
integration. Before the fix, all ACP tasks failed silently. After
patching both this code path and acpx's `shouldFallbackToNewSession()`
([openclaw/acpx#30](openclaw/acpx#30)), sessions
fall back to `session/new` correctly.

Fixes #338
Closes #361
Closes #362

---------

Co-authored-by: Ben Brandt <benjamin.j.brandt@gmail.com>

Author: maskedband1t

src/acp-agent.ts

@@ -1218,7 +1218,19 @@ export class ClaudeAcpAgent implements Agent {
       nextPendingOrder: 0,
     };
 
-    const initializationResult = await q.initializationResult();
+    let initializationResult;
+    try {
+      initializationResult = await q.initializationResult();
+    } catch (error) {
+      if (
+        creationOpts.resume &&
+        error instanceof Error &&
+        error.message === "Query closed before response received"
+      ) {
+        throw RequestError.resourceNotFound(sessionId);
+      }
+      throw error;
+    }
 
     const models = await getAvailableModels(q, initializationResult.models, settingsManager);