Long-running builds

bazel-mcp can keep ordinary calls synchronous or return durable task handles when the MCP client declares compatible task support.

Default: automatic negotiation

mcp_execution_policy = "auto"
task_ttl_seconds = 86400
task_poll_interval_ms = 2000

With auto, the server selects the protocol flow from capabilities negotiated for the current request:

Client capability	Execution behavior
No compatible task support	Ordinary synchronous tools/call result
MCP 2025-11-25 legacy tasks	Nested task handle, then task protocol methods
Tasks extension	Extension task result and polling methods

The task ID is also the Bazel invocation ID, so accepted work is immediately addressable for status, result retrieval, inspection, and cancellation.

Policy choices

• auto is the recommended default.
• sync_only always returns an ordinary CallToolResult for new calls.
• tasks_required rejects bazel.run before Bazel starts when the client did not declare compatible task support.

Changing policy does not strand existing unexpired task handles. They remain readable and cancellable after restart or configuration changes.

Expiration and recovery

The task TTL is the minimum time a terminal task result remains available. A queued or running task does not expire. The polling interval is advisory so clients can avoid excessive status traffic.

For complete settings and constraints, see configuration.