fix(matrix): route text-only send_message through adapter for E2EE support

[teknium1]

Summary

Text-only Matrix messages sent via the send_message engine (hermes send, cron deliver: matrix) now arrive encrypted in E2EE rooms instead of cleartext (red padlock).

Root cause: media sends already routed through the mautrix adapter (_send_matrix_via_adapter), which encrypts. Text-only sends took the raw-HTTP standalone_sender_fn path, which never encrypts — so text landed unencrypted in E2EE rooms.

Changes

• tools/send_message_tool.py: route all Matrix sends through _send_matrix_via_adapter (drop the and media_files gate); remove the now-dead _registry_standalone_send("matrix", ...) branch from the text-only loop. The adapter reuses the live gateway's E2EE session when available ([Bug]: send_message Matrix (media) path reconnects + re-inits E2EE per message — exhausts recipient one-time keys and silently drops messages under burst #46310) and falls back to an encryption-aware ephemeral adapter for standalone/cron.
• tests/tools/test_send_message_tool.py: invert test_matrix_text_only_* to assert the adapter path (was asserting the raw-HTTP path — the bug).

The plugin's standalone_sender_fn stays registered for the registry contract; it is simply no longer reached for Matrix.

Validation

	Before	After
Text-only send in E2EE room	raw HTTP m.text → cleartext (red padlock)	mautrix adapter → encrypted
Media send in E2EE room	adapter → encrypted	adapter → encrypted (unchanged)
Targeted tests	—	169/169 pass
E2E routing check	text → standalone raw-HTTP	text → _send_matrix_via_adapter, raw-HTTP bypassed

Salvaged from #20259 (@DanAsBjorn, first submitter) onto current main. The original patched the pre-#41112 _send_matrix branch, which had since moved to the plugin's standalone path — same fix direction, re-applied to the current structure. Duplicate #23382 (@32r4) fixed the same routing layer with an encryption-flag gate; the unconditional route is simpler and correct since the adapter sends plaintext to unencrypted rooms fine.

Infographic

[alt-glitch]

This was generated by AI during triage.

Salvage of #20259 (@DanAsBjorn) re-applied to current main. Competes with the same-goal PRs #23382 (routes text through the adapter behind an encryption flag) and #45518 (adds an explicit E2EE encryption guard in send()/edit_message()) — same silent-cleartext-in-E2EE family, different mechanisms. Related, not duplicate; a maintainer should pick the canonical fix.