buzz channels set-add-policy replaces the caller's whole kind:10100 agent profile, erasing name and respond_to #4490

buzz channels set-add-policy overwrites the caller's whole kind:10100 agent profile, silently erasing name and respond_to.

Where. crates/buzz-cli/src/commands/channels.rs (cmd_set_add_policy) builds the event with the policy as the entire content:

let content = serde_json::json!({ "channel_add_policy": policy }).to_string();
use nostr::{EventBuilder, Kind};
let builder = EventBuilder::new(
    Kind::Custom(buzz_sdk::kind::KIND_AGENT_PROFILE as u16),
    &content,
)
.tags([]);

Why it destroys state. Kind 10100 is KIND_AGENT_PROFILE (crates/buzz-core/src/kind.rs:87) and is replaceable, keyed by pubkey (kind.rs:841 asserts is_replaceable; handlers/ingest.rs:421 notes "user-owned replaceable, keyed by pubkey"). The same event kind carries an agent's name and respond_to (desktop/src-tauri/src/nostr_convert.rs:441; test fixture at :933 is {"name":"Scout","respond_to":"anyone"}).

So when an agent identity runs set-add-policy, the relay replaces that agent's directory entry with a blob containing only channel_add_policy.

Downstream effect. The agent then fails relayAgentIsSharedWithUser (desktop/src/features/messages/lib/agentAutocompleteEligibility.ts:12, which requires agent.respondTo === "anyone"), so it silently drops out of teammates' mention autocomplete. No error, no obvious cause, and the recovery is non-obvious.

Suggested fix, either works:

• read-modify-write the existing kind:10100 content instead of replacing it, or
• move channel_add_policy to its own kind.

Found by reading main @ b1b283c, not observed in the wild. Flagging because the failure mode is silent.

Related: #4489 (mention autocomplete), #4487 / #4488 (respond_to propagation).