Deflake acceptance tests (#3672)

## Changes

This PR makes some tactical changes to the acceptance test configuration
to deflake them. They've been quite flaky for me, especially in agent
settings. I asked an agent to stress test them and address problems:
* The default timeout for tests is now 30s instead of 20s (common cause
of failures)
* run-local-node tests now automatically use a free port (very common
cause of failures)
* The `timeout` self-test is less timing sensitive (rare cause of
failures)

## Tests
* Stress tested by AI

Author: lennartkats-db

acceptance/cmd/workspace/apps/run-local-node/script

@@ -4,9 +4,14 @@ cd app
 # so we don't need to start it in background. It will install the dependencies as part of the command
 trace $CLI apps run-local --prepare-environment --entry-point test.yml 2>&1 | grep -w "Hello, world"
 
-PORT=8080
-DEBUG_PORT=5252
-PROXY_PORT=8081
+# Function to find a free port in safe range
+get_free_port() {
+    python3 -c "import socket,random; port=random.randint(49152,65535); s=socket.socket(); s.bind(('',port)); print(port); s.close()" 2>/dev/null || python3 -c "import socket; s=socket.socket(); s.bind(('',0)); print(s.getsockname()[1]); s.close()"
+}
+
+PORT=$(get_free_port)
+DEBUG_PORT=$(get_free_port)
+PROXY_PORT=$(get_free_port)
 
 cleanup() {
     # Kill any still running processes on these ports when the script exits

acceptance/selftest/timeout/output.txt

@@ -1,4 +1,4 @@
 
->>> sleep 2
+>>> sleep 4
 
 Error: Test script killed due to a timeout

acceptance/selftest/timeout/script

@@ -1,2 +1,2 @@
-trace sleep 2
+trace sleep 4
 echo "This is never printed"

acceptance/selftest/timeout/test.toml

@@ -1,5 +1,4 @@
-# Manually check that test takes about 0.1s:
-# PASS: TestAccept/selftest/timeout (0.10s)
-Timeout = '100ms'
-TimeoutWindows = '300ms'
-TimeoutCloud = '300ms'
+# Test that timeout mechanism works (script sleeps 4s but should be killed much sooner)
+Timeout = '500ms'
+TimeoutWindows = '500ms'
+TimeoutCloud = '500ms'

acceptance/test.toml

@@ -3,7 +3,7 @@ Local = true
 Cloud = false
 
 # default timeouts
-Timeout = '20s'
+Timeout = '30s'
 TimeoutWindows = '60s'
 
 # Slowest test I saw: