fix(line): use build_source not create_source so inbound messages dispatch

[wuwushi4]

Summary

The LINE Messaging API plugin added in #23197 has a typo that causes 100% of inbound text messages to crash before they reach the agent. _handle_message_event calls self.create_source(...) at plugins/platforms/line/adapter.py:962, but the base adapter's helper is named build_source — every other platform adapter (mattermost, matrix, whatsapp, msgraph_webhook, wecom, feishu, bluebubbles, qqbot) calls self.build_source(...).

Reproduces every time you send any text to a LINE bot configured via this plugin. The webhook is received, signature verified, event dispatched — then dies in _handle_message_event with:

ERROR hermes_plugins.line_platform.adapter: LINE: dispatch_event failed
  File ".../plugins/platforms/line/adapter.py", line 877, in _handle_webhook
  File ".../plugins/platforms/line/adapter.py", line 910, in _dispatch_event
  File ".../plugins/platforms/line/adapter.py", line 962, in _handle_message_event
AttributeError: 'LineAdapter' object has no attribute 'create_source'

The kwargs at the call site (chat_id, chat_type, user_id, user_name, chat_name) already match build_source's signature exactly — pure rename, zero behavior change. Verified locally: after the one-character fix, inbound messages dispatch normally, agent responds via the free reply token, and the postback fallback path also works.

Why the test suite didn't catch this

tests/gateway/test_line_plugin.py (644 lines) covers signature verification, parsing, the postback state machine, etc., but doesn't appear to exercise the full webhook → _handle_message_event → build_source → MessageEvent path against a real LineAdapter instance — so the missing-attribute crash hides behind the unit-test boundary. Worth a follow-up to add an end-to-end smoke test that constructs a real adapter and feeds it a parsed message event.

Test plan

• Inbound text DM dispatches to agent and gets a reply (verified locally on a real LINE OA + ngrok tunnel)
• Reply token path is used (free; no Push API call)
• Group / room dispatch (untested locally — same code path, same fix applies)

🤖 Generated with Claude Code

[alt-glitch]

Duplicate of #23305 — same one-line fix (create_source → build_source) in LINE adapter. Both address the AttributeError crash on inbound messages.

[wuwushi4]

Thanks for the pointer to #23305 — happy to defer, that PR's session-source fix is more comprehensive than the bare typo correction here. Closing in favor of #23305.