feat(acp): carry provider key onto ACPAgent via create_agent

The authoritative ACP provider key lives on ACPAgentSettings.acp_server
('claude-code', 'codex', 'gemini-cli', 'custom'), but create_agent() dropped it
when building the runtime ACPAgent — which kept only acp_command. The launch
command does not reliably reverse-map to a provider (detect_acp_provider_by_command
returns None for the common `npx -y @zed-industries/claude-code-acp` and
`npx -y @openai/codex acp` forms), so downstream consumers had no dependable way
to recover the provider from a serialized agent.

Add an optional `acp_server: str | None` field to ACPAgent, populated by
create_agent() from the settings. It then rides ConversationInfo.agent, giving
the conversation UI an authoritative key to resolve a provider brand label /
model list without reverse-parsing the command or hand-stamping a tag. Additive
and backward-compatible: defaults to None for agents built directly (not from
settings) and for older serialized payloads.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: Simon Rosenberg

openhands-sdk/openhands/sdk/agent/acp_agent.py

@@ -1270,6 +1270,20 @@ class ACPAgent(AgentBase):
             " ['npx', '-y', '@agentclientprotocol/claude-agent-acp']"
         ),
     )
+    acp_server: str | None = Field(
+        default=None,
+        description=(
+            "Provider registry key identifying which ACP CLI this agent runs "
+            "('claude-code', 'codex', 'gemini-cli', or 'custom'); None when the "
+            "agent is built directly rather than via ACPAgentSettings. Set by "
+            "ACPAgentSettings.create_agent() from ACPAgentSettings.acp_server so "
+            "the authoritative key survives onto the agent — and thus onto "
+            "ConversationInfo.agent — because the launch command in acp_command "
+            "does not reliably reverse-map to a provider. Informational only: "
+            "consumers use it to resolve a provider brand label / model list; "
+            "the subprocess is still launched from acp_command."
+        ),
+    )
     acp_args: list[str] = Field(
         default_factory=list,
         description="Additional arguments for the ACP server command",

openhands-sdk/openhands/sdk/settings/model.py

@@ -1724,6 +1724,11 @@ def create_agent(self) -> ACPAgent:
         return ACPAgent(
             llm=self.llm,
             acp_command=self.resolve_acp_command(),
+            # Carry the authoritative provider key onto the agent: acp_command
+            # alone does not reliably reverse-map to a provider, so consumers
+            # (e.g. the conversation UI resolving a brand label / model list)
+            # read it from ConversationInfo.agent.acp_server.
+            acp_server=self.acp_server,
             acp_args=list(self.acp_args),
             # Pass acp_env directly rather than via resolve_acp_env() so the
             # deprecation warning is not emitted twice on the create_agent path:

tests/sdk/test_settings.py

@@ -886,6 +886,31 @@ def test_acp_create_agent_uses_server_default_command(
         "@agentclientprotocol/claude-agent-acp@0.30.0",
     ]
     assert agent.acp_model == "claude-opus-4-6"
+    # The authoritative provider key is carried onto the agent.
+    assert agent.acp_server == "claude-code"
+
+
+def test_acp_create_agent_carries_provider_key() -> None:
+    """``create_agent`` stamps the provider key onto the agent for every choice.
+
+    ``acp_command`` does not reliably reverse-map to a provider, so the key must
+    ride the agent (and thus ``ConversationInfo.agent``) for consumers to resolve
+    a brand label / model list. Custom carries through verbatim; an agent built
+    directly (not from settings) defaults to ``None``; and the key survives a
+    serialization round-trip through the ``AgentBase`` discriminated union.
+    """
+    for server in ("claude-code", "codex", "gemini-cli", "custom"):
+        kwargs: dict[str, Any] = {"acp_server": server}
+        if server == "custom":
+            kwargs["acp_command"] = ["my-acp"]
+        agent = ACPAgentSettings(**kwargs).create_agent()
+        assert agent.acp_server == server
+
+    assert ACPAgent(acp_command=["x"]).acp_server is None
+
+    agent = ACPAgentSettings(acp_server="gemini-cli").create_agent()
+    reloaded = ACPAgent.model_validate_json(agent.model_dump_json())
+    assert reloaded.acp_server == "gemini-cli"
 
 
 def test_acp_resolve_command_for_known_servers(