…) hook

Refactor the inlined `re.sub(...)[:4000].strip()` cleanup at the
auto-TTS site in `_process_message_background` into an overridable
method `BasePlatformAdapter.prepare_tts_text(text: str) -> str`.

The default implementation is byte-identical to the previous inline
expression — strip `* _ \` # [ ] ( )` and truncate to 4000 chars — so
every existing adapter (Telegram, Discord, Slack, Matrix, IRC, etc.)
gets exactly the same behaviour as before. Zero behaviour change for
any consumer that doesn't override the method.

Why add the hook: voice-first platform adapters need stricter
cleanup than text-bubble platforms. The default strips a handful of
markdown sigils, which is fine when the output goes into a Discord
embed or a Telegram message bubble — but read aloud by a TTS engine,
URLs (`https://example.com/foo`), fenced code blocks, file paths
(`/Users/x/foo.py`), and `MEDIA:` tags turn into long sequences of
unintelligible characters. With this hook an adapter can drop those
spans before TTS while leaving the data-channel transcript intact
for visual rendering.

Without the hook, voice adapters have to either
  - duplicate the auto-TTS flow inside their own `handle_response`
    pipeline, which means re-implementing the entire `extract_media`,
    `extract_images`, `extract_local_files`, attachment routing and
    error-handling sequence in `_process_message_background`, or
  - live with TTS speaking URLs character-by-character.

Both are worse than a 7-line method addition.

Example consumer:
  https://github.com/kortexa-ai/hermes-livekit — LiveKit WebRTC voice
  gateway plugin. Its `LiveKitAdapter.prepare_tts_text()` additionally
  strips fenced code blocks, inline code, URLs, file paths, and
  `MEDIA:` tags before TTS synthesis, while the full response still
  reaches connected clients via the data channel. Drop-in installable
  via `pip install git+https://github.com/kortexa-ai/hermes-livekit.git`.

Carved out of #3894 (LiveKit WebRTC gateway PR) so the generic hook
can land independently of the LiveKit platform itself.

…th of resolve_provider_client

In resolve_provider_client(), the named custom provider code path at
~line 2914 only checked the ``key_env`` field when looking for an
environment-variable-based API key. The documented ``api_key_env``
snake_case alias was silently ignored, causing custom providers
configured with ``api_key_env`` to fall through to the
``no-key-required`` placeholder — which produces a confusing 401
(``****ired`` mask) on auth-required remote endpoints.

This mirrors the same fix already applied to run_agent.py in commit
6ddc48b (fix(fallback): resolve api_key_env in fallback chain entries).

Also adds a logger.warning() when the placeholder is reached, so
future alias gaps are easier to debug.

Closes #25091

_OPENROUTER_MODEL hardcoded 'google/gemini-3-flash-preview' which
returns 404 on OpenRouter, breaking all vision tasks for users who
rely on the OpenRouter default.  Additionally, _try_openrouter()
ignored the user-configured auxiliary.vision.model entirely.

Changes:
- Update _OPENROUTER_MODEL default to google/gemini-2.5-flash (valid)
- Add optional 'model' parameter to _try_openrouter()
- Pass configured model from _resolve_strict_vision_backend() through
  to _try_openrouter()

This allows users who set auxiliary.vision.model (e.g. x-ai/grok-4.3)
to have it actually used, while maintaining backward compatibility.

_LineClient's five aiohttp.ClientSession() calls omit trust_env=True,
silently bypassing HTTP_PROXY / HTTPS_PROXY / ALL_PROXY. Result: every
LINE API call (reply, push, loading, fetch_content, get_bot_user_id)
ignores the system proxy.

Fix: add trust_env=True to all five session constructions. Symmetric
with the wecom and weixin adapters which already set this flag. No
behavior change for users not behind a proxy.

…tors

Adds release-note attribution mappings for 9 contributors from group 4:
- @EloquentBrush0x (PR #26657)
- @subtract0 (PR #25658)
- @zwolniony (PR #26961)
- @that-ambuj (PR #26582)
- @zccyman (PR #25294)
- @lidge-jun (PR #26814)
- @phoenixshen (PR #26768)
- @AhmetArif0 (PR #26635)
- (francip already mapped from prior PR #26134 attribution)

#27147 dropped from this batch — already landed on main as 4b17c24.