fix(lsp): Start JSON-RPC requests after the notifications before them

ide-jsonrpc handled incoming notifications in order on a dedicated thread
but started each incoming request on its own blocking task right away, so
a request could be handled before a notification that arrived ahead of
it. The mock language server in the ide-lsp tests answered
`textDocument/references` before applying the `didOpen` of a file opened
for a project-wide search (missing results, a search finishing before the
test could cancel it or open the file), and on the client side an ACP
`session/request_permission` could overtake the `session/update` that
announced its tool call (ide-agent polled for up to 200 ms to cover it).

A request now starts once every notification received before it has been
handled; requests still run concurrently. The ide-agent polling is gone.

Tests no longer depend on timing:
- the references tests hold the mock's answer with a gate and cancel or
  open the file while it is held, instead of sleeping and measuring;
- the indexing retry ends indexing once the first answer is out;
- the crash/restart test counts Ready/Crashed statuses instead of reading
  the last one, which a restart can already have replaced;
- the mock records a notification under the same lock as its effect, and
  `eventually` waits up to 30 s;
- the TCP tests hold their port bound (not listening) instead of freeing
  it for another test to take, and listen only after the command started.

Claude-Session: https://claude.ai/code/session_01VUYsdXA2nkF5v6zsC93dpn

crates/ide-agent/src/lib.rs

@@ -923,15 +923,6 @@ impl Task {
                     .collect()
             })
             .unwrap_or_default();
-        // The tool call it is about arrives as a notification on another thread: let it land first.
-        if let Some(tool) = params.pointer("/toolCall/toolCallId").and_then(Value::as_str) {
-            for _ in 0..20 {
-                if self.state.lock().timeline.has_tool(tool) {
-                    break;
-                }
-                std::thread::sleep(Duration::from_millis(10));
-            }
-        }
         let (tx, rx) = std::sync::mpsc::channel();
         let entry = self.push_entry(AgentEntry::Permission { id, title, options: options.clone(), chosen: None });
         self.permissions.lock().insert(id, tx);

crates/ide-agent/src/timeline.rs

@@ -37,10 +37,6 @@ impl Timeline {
         t
     }
 
-    pub fn has_tool(&self, id: &str) -> bool {
-        self.tools.contains_key(id)
-    }
-
     pub fn push(&mut self, entry: AgentEntry) -> usize {
         self.entries.push(entry);
         self.entries.len() - 1