Summary

channel_send tool unconditionally lowercases the channel parameter before adapter lookup. If a [[sidecar_channels]] entry has any uppercase letter in name (e.g. bot-A), channel_send(channel="bot-A", ...) fails with "channel not found" because the registered adapter key preserves the original case while the lookup key is folded to bot-a.

Plain text replies through the agent loop (incoming → outgoing same channel via sidecar) are unaffected — only the explicit channel_send tool path fails. This is most visible for voice / file attachments because they have no other delivery route.

Reproducer

1. Add a sidecar with a name containing uppercase:

[[sidecar_channels]]
name = "bot-A"
channel_type = "telegram"
...

2. From an agent with channel_send capability, call:

channel_send(channel="bot-A", recipient="<chat_id>", file_path="/path/to/audio.ogg")

3. Tool returns Channel Send failed — adapter "bot-A" not found.
4. Rename to lowercase (name = "bot-a") and the same call succeeds.

Root cause (verified by inspection at v2026.6.10-beta.17)

crates/librefang-runtime/src/tool_runner/channel.rs:140:

let channel = input["channel"]
    .as_str()
    .ok_or("Missing 'channel' parameter")?
    .trim()
    .to_lowercase();   // ← folds caller-supplied name

The lowercased value is then passed to kh.send_channel_media(&channel, ...) / kh.send_channel_text(...) which look up the adapter by exact key. Adapter registration (channel_bridge.rs, post-#5996) keeps sidecar_config.name.clone() as the account_id with its original case → lookup mismatch.

Suggested fix

Either:

• A. Drop the .to_lowercase() on caller input — caller-supplied case should match registration. (Simpler; behavior-preserving for already-lowercase setups.)
• B. Lowercase both sides consistently — fold at registration AND at lookup. Requires touching the registration path so existing in-the-wild capital-cased sidecars don't break silently.

(A) is minimal and matches the intent visible in #5996 (preserve sidecar name as the routing key).

Impact

• Multi-bot Telegram setups that use any capital in sidecar name cannot send voice/file via channel_send.
• Workaround: rename sidecar name to lowercase. Trade-off: dashboards / config remain harder to read.

Environment

• LibreFang 2026.6.10-beta.17
• macOS (aarch64)
• Sidecar: librefang-sidecar-telegram (Rust, bundled)
• Discovered while verifying Regression: /agent cross-bot leak returns in beta.16 — sidecar messages missing account_id in metadata #5955 fix in beta.17 — text routing isolation works as expected, voice path surfaced the residual fold.

Related

• Regression: /agent cross-bot leak returns in beta.16 — sidecar messages missing account_id in metadata #5955 / PR fix(channels): propagate per-sidecar account_id for multi-bot isolation (#5955) #5996 — account_id propagation that made this surface visible (qualified channel: telegram:<name> keys now preserve case at registration)
• Workaround on operator side has been used since 2026-05-31; filing now that the fix path is clear.