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Merged
benbrandt merged 3 commits into from
Jun 26, 2026
Merged

fix(unstable-v2): make mcpServers optional in new sessions #1523

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7bf2471
fix(schema): tolerate invalid items in new session lists
benbrandt Jun 26, 2026
723645b
fix(unstable-v2): make mcpServers optional in new sessions
benbrandt Jun 26, 2026
8d6700c
Update test assertions
benbrandt Jun 26, 2026
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5 changes: 5 additions & 0 deletions agent-client-protocol-schema/src/v1/agent.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -918,6 +918,7 @@ impl AuthMethodTerminal {
/// Request parameters for creating a new session.
///
/// See protocol docs: [Creating a Session](https://agentclientprotocol.com/protocol/session-setup#creating-a-session)
#[serde_as]
#[skip_serializing_none]
#[derive(Debug, Clone, Serialize, Deserialize, JsonSchema, PartialEq, Eq)]
#[schemars(extend("x-side" = "agent", "x-method" = SESSION_NEW_METHOD_NAME))]
Expand All @@ -931,9 +932,13 @@ pub struct NewSessionRequest {
/// These expand the session's filesystem scope without changing `cwd`, which
/// remains the base for relative paths. When omitted or empty, no
/// additional roots are activated for the new session.
#[serde_as(deserialize_as = "DefaultOnError<VecSkipError<_, SkipListener>>")]
#[schemars(extend("x-deserialize-default-on-error" = true, "x-deserialize-skip-invalid-items" = true))]
#[serde(default, skip_serializing_if = "Vec::is_empty")]
pub additional_directories: Vec<PathBuf>,
/// List of MCP (Model Context Protocol) servers the agent should connect to.
#[serde_as(deserialize_as = "DefaultOnError<VecSkipError<_, SkipListener>>")]
#[schemars(extend("x-deserialize-default-on-error" = true, "x-deserialize-skip-invalid-items" = true))]
pub mcp_servers: Vec<McpServer>,
/// The _meta property is reserved by ACP to allow clients and agents to attach additional
/// metadata to their interactions. Implementations MUST NOT make assumptions about values at
Expand Down
8 changes: 6 additions & 2 deletions agent-client-protocol-schema/src/v2/agent.rs
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Expand Up @@ -994,6 +994,7 @@ impl AuthMethodTerminal {
/// Request parameters for creating a new session.
///
/// See protocol docs: [Creating a Session](https://agentclientprotocol.com/protocol/session-setup#creating-a-session)
#[serde_as]
#[skip_serializing_none]
#[derive(Debug, Clone, Serialize, Deserialize, JsonSchema, PartialEq, Eq)]
#[schemars(extend("x-side" = "agent", "x-method" = SESSION_NEW_METHOD_NAME))]
Expand All @@ -1007,9 +1008,14 @@ pub struct NewSessionRequest {
/// These expand the session's workspace scope without changing `cwd`, which
/// remains the base for relative paths. When omitted or empty, no
/// additional roots are activated for the new session.
#[serde_as(deserialize_as = "DefaultOnError<VecSkipError<_, SkipListener>>")]
#[schemars(extend("x-deserialize-default-on-error" = true, "x-deserialize-skip-invalid-items" = true))]
#[serde(default, skip_serializing_if = "Vec::is_empty")]
pub additional_directories: Vec<PathBuf>,
/// List of MCP (Model Context Protocol) servers the agent should connect to.
#[serde_as(deserialize_as = "DefaultOnError<VecSkipError<_, SkipListener>>")]
#[schemars(extend("x-deserialize-default-on-error" = true, "x-deserialize-skip-invalid-items" = true))]
#[serde(default, skip_serializing_if = "Vec::is_empty")]
pub mcp_servers: Vec<McpServer>,
/// The _meta property is reserved by ACP to allow clients and agents to attach additional
/// metadata to their interactions. Implementations MUST NOT make assumptions about values at
Expand Down Expand Up @@ -5649,7 +5655,6 @@ mod test_serialization {
serde_json::to_value(NewSessionRequest::new("/home/user/project")).unwrap(),
json!({
"cwd": "/home/user/project",
"mcpServers": []
})
);
assert_eq!(
Expand All @@ -5666,7 +5671,6 @@ mod test_serialization {
"/home/user/shared-lib",
"/home/user/product-docs"
],
"mcpServers": []
})
);
assert_eq!(
Expand Down
2 changes: 1 addition & 1 deletion docs/protocol/v2/draft/schema.mdx
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Expand Up @@ -1278,7 +1278,7 @@ additional roots are activated for the new session.
<ResponseField name="cwd" type={"string"} required>
The working directory for this session. Must be an absolute path.
</ResponseField>
<ResponseField name="mcpServers" type={<a href="#mcpserver">McpServer[]</a>} required>
<ResponseField name="mcpServers" type={<a href="#mcpserver">McpServer[]</a>} >
List of MCP (Model Context Protocol) servers the agent should connect to.
</ResponseField>

Expand Down
2 changes: 1 addition & 1 deletion docs/protocol/v2/schema.mdx
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Original file line number Diff line number Diff line change
Expand Up @@ -520,7 +520,7 @@ additional roots are activated for the new session.
<ResponseField name="cwd" type={"string"} required>
The working directory for this session. Must be an absolute path.
</ResponseField>
<ResponseField name="mcpServers" type={<a href="#mcpserver">McpServer[]</a>} required>
<ResponseField name="mcpServers" type={<a href="#mcpserver">McpServer[]</a>} >
List of MCP (Model Context Protocol) servers the agent should connect to.
</ResponseField>

Expand Down
8 changes: 6 additions & 2 deletions schema/v1/schema.json
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Expand Up @@ -3456,14 +3456,18 @@
"type": "array",
"items": {
"type": "string"
}
},
"x-deserialize-default-on-error": true,
"x-deserialize-skip-invalid-items": true
},
"mcpServers": {
"description": "List of MCP (Model Context Protocol) servers the agent should connect to.",
"type": "array",
"items": {
"$ref": "#/$defs/McpServer"
}
},
"x-deserialize-default-on-error": true,
"x-deserialize-skip-invalid-items": true
},
"_meta": {
"description": "The _meta property is reserved by ACP to allow clients and agents to attach additional\nmetadata to their interactions. Implementations MUST NOT make assumptions about values at\nthese keys.\n\nSee protocol docs: [Extensibility](https://agentclientprotocol.com/protocol/extensibility)",
Expand Down
8 changes: 6 additions & 2 deletions schema/v1/schema.unstable.json
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Expand Up @@ -6289,14 +6289,18 @@
"type": "array",
"items": {
"type": "string"
}
},
"x-deserialize-default-on-error": true,
"x-deserialize-skip-invalid-items": true
},
"mcpServers": {
"description": "List of MCP (Model Context Protocol) servers the agent should connect to.",
"type": "array",
"items": {
"$ref": "#/$defs/McpServer"
}
},
"x-deserialize-default-on-error": true,
"x-deserialize-skip-invalid-items": true
},
"_meta": {
"description": "The _meta property is reserved by ACP to allow clients and agents to attach additional\nmetadata to their interactions. Implementations MUST NOT make assumptions about values at\nthese keys.\n\nSee protocol docs: [Extensibility](https://agentclientprotocol.com/protocol/extensibility)",
Expand Down
10 changes: 7 additions & 3 deletions schema/v2/schema.json
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Expand Up @@ -4036,22 +4036,26 @@
"type": "array",
"items": {
"type": "string"
}
},
"x-deserialize-default-on-error": true,
"x-deserialize-skip-invalid-items": true
},
"mcpServers": {
"description": "List of MCP (Model Context Protocol) servers the agent should connect to.",
"type": "array",
"items": {
"$ref": "#/$defs/McpServer"
}
},
"x-deserialize-default-on-error": true,
"x-deserialize-skip-invalid-items": true
},
"_meta": {
"description": "The _meta property is reserved by ACP to allow clients and agents to attach additional\nmetadata to their interactions. Implementations MUST NOT make assumptions about values at\nthese keys.\n\nSee protocol docs: [Extensibility](https://agentclientprotocol.com/protocol/extensibility)",
"type": ["object", "null"],
"additionalProperties": true
}
},
"required": ["cwd", "mcpServers"],
"required": ["cwd"],
"x-side": "agent",
"x-method": "session/new"
},
Expand Down
10 changes: 7 additions & 3 deletions schema/v2/schema.unstable.json
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Expand Up @@ -6949,22 +6949,26 @@
"type": "array",
"items": {
"type": "string"
}
},
"x-deserialize-default-on-error": true,
"x-deserialize-skip-invalid-items": true
},
"mcpServers": {
"description": "List of MCP (Model Context Protocol) servers the agent should connect to.",
"type": "array",
"items": {
"$ref": "#/$defs/McpServer"
}
},
"x-deserialize-default-on-error": true,
"x-deserialize-skip-invalid-items": true
},
"_meta": {
"description": "The _meta property is reserved by ACP to allow clients and agents to attach additional\nmetadata to their interactions. Implementations MUST NOT make assumptions about values at\nthese keys.\n\nSee protocol docs: [Extensibility](https://agentclientprotocol.com/protocol/extensibility)",
"type": ["object", "null"],
"additionalProperties": true
}
},
"required": ["cwd", "mcpServers"],
"required": ["cwd"],
"x-side": "agent",
"x-method": "session/new"
},
Expand Down