[FEATURE] Workflow tool: no fail-fast on rate-limit/quota exhaustion across concurrent subagents

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

When a Workflow-orchestrated run fans out many concurrent agent() calls (e.g. claude-security:scan's researcher/verifier panels), hitting an account usage limit mid-run isn't surfaced early. Individual agent() calls retry internally and, on a terminal API error, silently resolve to null rather than propagating a distinguishable "quota exhausted" signal — so the orchestrating script just keeps dispatching new agents into the same wall. The only way to notice is after the fact, inspecting a suspiciously thin result set or waiting for the whole task to finish.

Proposed Solution

Suggested improvement: a circuit-breaker at the Workflow concurrency-manager level — when a terminal API error is specifically classified as rate-limit/usage-cap (429/quota, not a generic transient failure already covered by the built-in retry), stop dispatching new agent() calls and surface a clear "halted: usage limit hit" status to the calling script/user, instead of quietly running every queued call down to its own failure.

Alternative Solutions

_No response_

Priority

Critical - Blocking my work

Feature Category

CLI commands and flags

Use Case Example

_No response_

Additional Context

_No response_