Foundation primitive for the native+pluggable runtime principle (task
#117, blocks #87). Lets each adapter declare which cross-cutting
capabilities it owns natively (heartbeat, scheduler, durable session,
status mgmt, retry, activity decoration, channel dispatch) versus
delegates to the platform's fallback implementation.
Pure additive: every existing adapter inherits BaseAdapter.capabilities()
which returns RuntimeCapabilities() — every flag False — so today's
"platform owns everything" behavior is preserved exactly. Subsequent
PRs land platform-side consumers (idle-timeout override, scheduler
skip, status-transition hook, etc.) one capability at a time.
Why a frozen dataclass instead of class attributes: capabilities are
declared at class-load time and read by the platform on every heartbeat.
A mutable value would let a runtime change capabilities mid-flight,
creating impossible-to-debug state where the platform's idea of who-
owns-heartbeat drifts from the adapter's actual code.
Why a `to_dict()` with explicit short keys: the Go side will read these
from the heartbeat payload by string key. The dict's wire names are
pinned independently of Python field names so a Python-side rename
doesn't silently break the Go consumer (test pins this).
Tests (9 new):
- is a frozen dataclass (mutation rejected)
- all 7 default flags are False (load-bearing — flipping any default
silently moves ownership for langgraph/crewai/deepagents)
- to_dict() keys are stable wire names (Go contract)
- BaseAdapter.capabilities() default returns all-False
- subclass override mechanism works
- sibling adapters' defaults aren't affected by an override
Verification:
- 1300/1300 workspace pytest pass (was 1291, +9)
- Zero behavior change for any existing code path
See project memory `project_runtime_native_pluggable.md`.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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