[DRAFT] fix(agent): route copilot-acp through non-streaming request flow

[MestreY0d4-Uninter]

Depends on #4536.
Please review/merge this after the ACP tool-call bridge lands, since this follow-up assumes that base behavior.

I’m opening it early to reduce the risk of upstream drift while #4536 is still pending.

Summary

This PR fixes the run_agent.py integration path for copilot-acp.

ACP should not go through the generic streaming request flow used by other providers. Doing so can lead to double-send behavior and makes interruption/abort handling less reliable.

What changed

• bypass the generic streaming path for copilot-acp
• route ACP through the non-streaming request path
• ensure shared ACP client interruption/abort is handled correctly
• detect ACP both by provider and ACP marker base URL
• add focused integration tests around ACP request routing and notice behavior

Why

The ACP client became much stronger after the tool-call bridge, but run_agent.py still treated it too much like a generic provider.

This PR fixes that integration mismatch.

Validation

Automated

• python3 -m py_compile agent/copilot_acp_client.py run_agent.py tests/test_run_agent.py
• uv run --extra dev python -m pytest -o addopts='' tests/test_run_agent.py -q -k 'CopilotAcpIntegration or CopilotAcpNotice'
• Result: 5 passed, 226 deselected

Manual

Validated end-to-end on the rebased branch with a real AIAgent(provider='copilot-acp') run:

• prompt: Reply exactly ACP_OK
• result: ACP_OK

Notes

This PR is about correct ACP integration in the main agent loop.
It does not change broader routing policy beyond the ACP-specific request path.

[MestreY0d4-Uninter]

Stacked follow-up to #4536.

Opened as draft to avoid upstream drift while the base ACP tool-call bridge is still pending.
Please review/merge this after #4536.

Related follow-ups in the same stack:

• [DRAFT] fix(agent): preserve copilot-acp session context across requests #5335 — ACP session/context preservation
• [DRAFT] fix(tools): support delegation reasoning overrides for subagents #5337 — delegation reasoning overrides

[MestreY0d4-Uninter]

Closing as stale/superseded by later ACP integration changes. I re-audited this against a clean origin/main worktree: the copilot-acp/run_agent integration area has evolved since this stacked draft was opened, so this PR is no longer the right review unit on top of current main. If there is still a remaining non-streaming gap, I'll re-extract it as a fresh focused PR against current main.