fix(agent): explicit error when workflow executor URL is not configured

[PMerlet]

Problem

When the agent receives a request on the workflow-executor proxy routes
(GET /_internal/workflow-executions/:runId, POST .../trigger) but the
workflowExecutorUrl option is not configured, the route was simply never
mounted. The client got a bare koa 404 with an empty body — indistinguishable
from a real "run not found" coming from the executor, and giving no hint that the
agent is actually misconfigured.

This came up debugging a staging agent where the deploying app didn't pass
workflowExecutorUrl: every workflow request 404'd with no actionable signal in
the browser console or the agent logs.

Change

• Mount the proxy route unconditionally (routes/index.ts).
• In the handler, if workflowExecutorUrl is missing, throw an
  InternalServerError with an explicit message
  (The workflow executor is not configured on this agent: the workflowExecutorUrl option is missing.).
  The agent's error-handling middleware turns this into a 500 with a clear
  detail for the client (instead of a silent 404), and logs it at Error level.

The constructor now tolerates a null URL instead of throwing at boot.

Tests

• handleProxy throws an explicit error when workflowExecutorUrl is not set.
• Constructor does not throw when the option is null.
• BASE_ROUTE_SIZE updated since the route is always mounted now.
• Existing proxy-forwarding tests unchanged and passing (21/21).

🤖 Generated with Claude Code

Note

Throw explicit error when workflow executor URL is not configured

• The workflow executor route in workflow-executor-proxy.ts now accepts a null executorUrl instead of requiring a valid URL at construction time.
• Routes in index.ts always register the WorkflowExecutorProxyRoute, regardless of whether workflowExecutorUrl is set.
• When the handler is invoked without a configured URL, it throws an InternalServerError with a descriptive message instead of returning a 404.
• Behavioral Change: previously, missing workflowExecutorUrl caused the route to be absent (404); now the route exists and returns a 500 with an explicit message.

^{Macroscope summarized da6e08e.}

[qltysh]

Coverage Impact

⬆️ Merging this pull request will increase total coverage on main by 0.01%.

Modified Files with Diff Coverage (1)

Rating	File	% Diff	Uncovered Line #s
	packages/agent/src/routes/workflow/workflow-executor-proxy.ts	100.0%
	Total	100.0%

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