fix(runtime): preserve resolved metadata in agent forks

[kshitijk4poor]

Summary

Curator and auxiliary agent forks now retain the complete resolved runtime bundle, including credential rotation, task request overrides, effective model/output limits, and ACP transport metadata.

Changes

• Preserve @infinitycrew39's curator credential-pool and request-override forwarding commits.
• Curator: honor resolved effective model, output cap, ACP transport, and auxiliary.curator.extra_body with task-local precedence.
• Background review: use the routed runtime's pool/overrides/model/cap/ACP metadata instead of the parent provider's pool.
• Delegation: forward resolved request overrides and output caps while retaining existing endpoint-aware pool resolution.
• Add regression coverage for curator, background-review, and delegated runtime handoff.

Validation

• 235 targeted tests passed on the final branch.
• Real isolated custom-provider E2E forced a stale-key 401, rotated to the valid pool credential, and preserved request metadata.
• Load-bearing negative controls failed at the expected parent boundaries.
• Ruff, py_compile, Windows-footgun scan, ty baseline comparison, and git diff --check passed.
• Final adversarial Codex review: clean.

Credit

Salvages #61567 by @infinitycrew39. Both contributor commits retain original authorship, followed by a separate maintainer widening commit.

Closes #61567

[alt-glitch]

This was generated by AI during triage.

Related: salvages #61567 (closed) and extends the just-merged #62077 (curator + background-review routing) to the delegation path (tools/delegate_tool.py: request-override + max_tokens forwarding, net-new vs #62077). Not a duplicate -- superset with net-new delegation content. Maintainer should decide whether to land the delegation extension on top of #62077.