feat: migrate relay integration to relaycast Rust SDK

[willwashburn]

Summary

• migrate Relay WS/HTTP integration to the published relaycast crate APIs
• update relay dependency to relaycast 0.2.4
• require handler_agent_id for command.invoked mapping and route commands only to the targeted broker

Validation

• cargo check
• cargo test

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[khaliqgant]

Nice. Much cleaner

[devin-ai-integration]

Devin Review found 1 potential issue.

View 6 additional findings in Devin Review.

[devin-ai-integration]

🟡 register_agent_with_workspace_key always returns None for workspace_id, losing it from the registration response

The new SDK-based register_agent_with_workspace_key hardcodes None for the workspace_id tuple element at src/auth.rs:336, whereas the old code extracted the workspace_id field from the API response JSON.

Detailed Explanation

The old code extracted workspace_id from the registration response:

let workspace_id = data
    .get("workspace_id")
    .and_then(Value::as_str)
    .map(ToOwned::to_owned);
return Ok((agent_id, returned_name, token, workspace_id));

The new code always returns None:

return Ok((agent.id, agent.name, agent.token, None));

In finish_session (src/auth.rs:295-297), the workspace_id is resolved as:

let workspace_id = workspace_id_from_register
    .or(workspace_id_hint)
    .unwrap_or_else(|| "ws_unknown".to_string());

Since workspace_id_from_register is now always None, resolution depends entirely on workspace_id_hint. This hint is populated from cache (src/auth.rs:220-222) or from create_workspace (src/auth.rs:238). However, when a user sets RELAY_API_KEY in the environment and no cache file exists (first run, or cache was cleared), workspace_id_hint is None and no fresh workspace is created (the env key succeeds directly). The resulting workspace_id becomes "ws_unknown", which is persisted in the cache and carried forward to all subsequent sessions via rotate_token (src/auth.rs:195).

Impact: In the env-key-no-cache scenario, workspace_id is permanently set to "ws_unknown" instead of the real value from the API. This affects any downstream logic or logging that relies on a valid workspace_id.

Prompt for agents

In src/auth.rs, line 336, the register_agent_with_workspace_key function returns None for the workspace_id (4th tuple element). If the relaycast SDK's Agent struct includes a workspace_id field (or if it can be obtained from the RelayCast client after registration), use that value instead of None. If the SDK truly doesn't provide workspace_id in the registration response, consider making a separate workspace info API call to resolve it rather than falling back to 'ws_unknown'. Alternatively, if workspace_id is not critical, document this intentional change.

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