fix(skills): prevent IndexError in build_plan_path on whitespace-only input

[konsisumer]

Summary

• build_plan_path() crashes with IndexError when user_instruction is whitespace-only (e.g. " \n "), because .strip().splitlines() returns [] and then [0] is applied to the empty list.
• Split the expression into two steps: compute lines first, then index only when non-empty.

Test plan

• Pass whitespace-only string (" \n ") as user_instruction to build_plan_path — should return the default conversation-plan slug instead of crashing
• Pass normal string — slug generation unchanged
• Pass empty string / None — still returns default slug

Closes #7576

[konsisumer]

Rebased onto latest origin/main and fixed the failing test_email_in_session_discovery test.

Root cause: Commit baddb6f7 (fix(gateway): derive channel directory platforms from enum instead of hardcoded list) refactored build_channel_directory() to iterate over the Platform enum dynamically instead of hardcoding platform names. The test used inspect.getsource() to check for a literal "email" string in the function body, which no longer exists.

Fix: Updated the test to verify that Platform contains "email" and that it's not in the _SKIP_SESSION_DISCOVERY frozenset — this guarantees email gets session-based discovery through the enum iteration.

[konsisumer]

Closing: referenced_issue_closed. all referenced issues closed: [7576]

---

autocontrib · housekeeping · 2026-04-19T13:17:05Z