fix: catches SchemaError instead of ValidationError — validation failures unhandled

[k-rister]

Bug Report

Multiple bugs found in roadblock.py:

1. Wrong exception type for schema validation (Critical)

Line 552: except jsonschema.exceptions.SchemaError should be ValidationError. SchemaError is raised when the schema itself is malformed, not when data fails validation. Actual validation failures propagate as unhandled exceptions.

Line 1838: Same wrong exception type in user message validation.

2. Duplicate unreachable condition

Line 574: elif not "recipient" in message["payload"] is identical to the condition on line 568 — this branch is unreachable dead code.

3. Wrong sender_id in message_build_custom

Line 1965: Passes the string "personal-stream-created" instead of self.my_id as the sender_id. Messages built with this function will have the wrong sender identity.

4. Missing backoff() on redis connection errors

Lines 1237-1242: No backoff() call on redis ConnectionError/TimeoutError in stream_add — creates a tight busy-loop that hammers the redis server when it's temporarily unavailable, unlike other redis operations that use backoff.