[Bug]: The discovery of local servers probes test listeners and cannot be turned off #30687

Before submitting

• I searched existing issues and did not find a duplicate.
• I included enough detail to reproduce or investigate the problem.

Area

apps/server

Steps to reproduce

1. Connect a T3 Code client, and start an agent thread.

2. From that agent, run two local servers for 9 seconds:

   timeout 9 python3 -m http.server 0 --bind 127.0.0.1 > with.log 2>&1 &
   env -u T3CODE_THREAD_ID timeout 9 python3 -m http.server 0 --bind 127.0.0.1 > without.log 2>&1 &

3. Read the two logs.

Expected behavior

A user can turn the discovery of local servers off, or at least its probing. A test process that an agent starts gets no request that it did not ask for.

Any of these solves it. The first is the most useful:

1. A setting in settings.json and an environment variable (for example T3CODE_DISCOVER_LOCAL_SERVERS=false) that turns off the scan.
2. Probe only when the preview panel is open, not whenever a client is subscribed.
3. Probe only a listener that has lived for some time, for example 30 seconds, so short test listeners stay untouched.
4. Let a process opt out through an environment variable.

Actual behavior

with.log shows GET / HTTP/1.1 from 127.0.0.1, and without.log shows none. No setting turns this off.

While a client subscribes to subscribeDiscoveredLocalServers, PortDiscovery scans every 3 seconds. It finds each listener that a process with T3CODE_THREAD_ID in its environment owns, or that belongs to a T3 terminal, and sends GET / to it. We also saw a TLS client hello on such ports. A test process inherits the variable from the agent, so its short-lived fake servers count as servers to find.

Test fakes often count requests, or refuse a request they do not expect. The probe arrives about 2 seconds after the listener opens, so the result depends on timing. In Go test suites we saw:

• the proxy got 2 connections, want none
• A fake server failed the test because it got a GET / it does not answer.
• A fake server recorded an unsigned call that no test code made.

One test failed in 5 of 20 runs and another in 1 of 20 on an unchanged commit. The failures looked like load-related flakes, and finding the real cause took a long time. A server under development also sees a request that nobody made.

Impact

Minor bug or occasional failure

Version or commit

t3 v0.1.5

Environment

Linux, t3 serve, Claude Code as the agent provider, a T3 Code client connected

Logs or stack traces

127.0.0.1 - - [04/Nov/2026 08:01:45] "GET / HTTP/1.1" 200 -

Workaround

Unset T3CODE_THREAD_ID before a test run. This works, but every test command of an agent needs it, and an agent does not know it has to.