fix(native): honor LCM_DEFAULT_URL in the rust LCM transport

[jeff-hykin]

rust didn't respect LCM_DEFAULT_URL

https://lcm-proj.github.io/lcm/content/multicast-setup.html#choosing-a-ttl

[greptile-apps]

Greptile Summary

This change lets the native Rust LCM transport read LCM_DEFAULT_URL so it can join the multicast bus configured for Python modules. Focused execution found that malformed udpm:// endpoints still apply a valid ttl query parameter while falling back to the default group and port, creating a mixed configuration that contradicts the fallback warning. Align the parser behavior and warning before merging.

Confidence Score: 4/5

The URL fallback path needs correction or clearer semantics before merging because malformed endpoint values can still change the effective multicast TTL.

The malformed-group and malformed-port paths were both executed with a valid TTL and consistently produced the default endpoint with an overridden TTL.

Files Needing Attention: native/rust/dimos-module/src/lcm.rs, particularly the invalid group/port handling and subsequent TTL query parsing.

T-Rex Logs

What T-Rex did

• T-Rex produced a proof for the posted P2 finding and built a focused Rust test for an invalid endpoint with a valid TTL, which showed the full-fallback expectation failed and the partial-fallback observation test passed.
• T-Rex validated the contract behavior after changes, confirming that invalid endpoint variants now produce group=239.255.76.67, port=7667, ttl=42, and verified the TTL parsing logic in native/rust/dimos-module/src/lcm.rs at lines 64-75, with the warning in 64-67 followed by continued parsing and TTL assignment.

_{Ran code and verified through T-Rex}

Comments Outside Diff (1)

1. General comment

   Invalid udpm endpoint warning claims a full fallback while TTL is retained

   • Bug
     • For udpm://not-an-ip:7667?ttl=42 and udpm://239.255.76.67:not-a-port?ttl=42, options_from_url returns the default multicast group 239.255.76.67 and port 7667, but returns TTL 42 rather than default TTL 1.
   • Cause
     • After group/port parsing fails, the match arm logs a warning but does not return the default options; execution continues into the query loop, which parses and assigns ttl.
   • Fix
     • Either return options immediately after the invalid group/port warning to make behavior match the message, or revise the warning to explicitly state that endpoint defaults are retained while valid query options such as TTL are still applied. Add coverage for invalid group and invalid port with a valid TTL.

   _{Ran code and verified through T-Rex}

_{Reviews (1): Last reviewed commit: "fix(native): honor LCM_DEFAULT_URL in th..." | Re-trigger Greptile}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ All tests successful. No failed tests found.

@@           Coverage Diff           @@
##             main    #3740   +/-   ##
=======================================
  Coverage   77.58%   77.58%           
=======================================
  Files        1315     1315           
  Lines      124697   124697           
  Branches    10867    10867           
=======================================
+ Hits        96748    96750    +2     
+ Misses      24816    24814    -2     
  Partials     3133     3133           

Flag	Coverage Δ
OS-ubuntu-24.04-arm	74.23% <ø> (-0.01%)	⬇️
OS-ubuntu-latest	74.78% <ø> (+<0.01%)	⬆️
Py-3.10	74.77% <ø> (ø)
Py-3.11	74.77% <ø> (-0.01%)	⬇️
Py-3.12	74.77% <ø> (-0.01%)	⬇️
Py-3.13	74.78% <ø> (+<0.01%)	⬆️
Py-3.14	74.78% <ø> (-0.01%)	⬇️
Py-3.14t	74.77% <ø> (-0.01%)	⬇️
SelfHosted-Large	30.22% <ø> (+<0.01%)	⬆️
SelfHosted-Linux	34.74% <ø> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.
see 1 file with indirect coverage changes

🚀 New features to boost your workflow:

• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.