The TaskEvent API was removed in favor of a future OpenTelemetry
integration. The README should not document APIs that no longer
exist in the codebase.

Add new top-level sections for Tasks (dataclass, nested tracking,
proxy serialization, two-layer serialization) and Workers (gRPC
server, dedicated execution thread, bidirectional streaming).

Expand Routines with dispatch gate and coroutine vs async generator
semantics, Discovery with events and protocol internals, Load
balancing with error classification and worker connections, Security
with TLS modes and discovery filtering, and Error handling with
exception transmission and version compatibility.

Add stable pip install command. Remove task lifecycle events section.

Covers channel pooling lifecycle, reactive error detection via
gRPC/HTTP2, and the absence of keepalive ping configuration.

 (#40)

LocalWorker.__init__ was eagerly resolving WorkerCredentials properties
into grpc.ServerCredentials and grpc.ChannelCredentials — C extension
types that cannot be pickled. On spawn-based platforms (macOS),
multiprocessing.Process.start() pickles the WorkerProcess, causing a
TypeError.

Drop @Property from WorkerCredentials credential methods, store the
picklable dataclass through the subprocess boundary, and resolve gRPC
credential objects only at the point of use in _serve() and _stop().

BREAKING CHANGE: WorkerCredentials.server_credentials and
client_credentials are now methods (call with parentheses) instead of
properties. WorkerProcess accepts credentials (WorkerCredentials | None)
instead of server_credentials (ServerCredentialsType).

…tate

The _index dict accumulates LoadBalancerContext → WorkerConnection
references containing unpicklable grpc.ChannelCredentials objects.
When WorkerProxy.__reduce__ pickles a live lb instance for nested
dispatch, this causes a TypeError. The connection state is dead
weight — the restored proxy creates a fresh context and re-discovers
workers from scratch.

WorkerCredentials gains a module-level ContextVar, __enter__/__exit__
methods, and a current() classmethod. Workers set their credentials
into this ContextVar on startup so that unpickled proxies can resolve
peer credentials without serializing private key material.

BREAKING CHANGE: _token field added to frozen dataclass (excluded from
init, repr, compare, and equality — no behavioral break for existing
callers).

Credentials now live in WorkerCredentials.current() via ContextVar,
so RuntimeContext no longer needs to carry them. This separates
concerns ahead of RuntimeContext becoming a task-level dispatch
settings container.

BREAKING CHANGE: RuntimeContext no longer accepts a credentials
parameter or exposes a credentials property.

Wraps the entire server lifecycle in the WorkerCredentials context
manager so that nested proxies created during task execution can
resolve peer credentials from WorkerCredentials.current() instead
of requiring serialized credentials.

WorkerProxy now defaults to Undefined credentials and resolves them
from WorkerCredentials.current() at construction time. __reduce__
serializes options but omits credentials entirely — the restored
proxy re-resolves from the worker's ContextVar, implementing peer
authentication without credential delegation.

WorkerPool passes WorkerCredentials directly to WorkerProxy instead
of pre-resolving client credentials. WorkerConnection now accepts
grpc.ChannelCredentials directly.

Removes ChannelCredentialsType and resolve_channel_credentials from
base.py — the callable-credential indirection layer is no longer
needed now that WorkerCredentials.client_credentials() is the sole
resolution path.

BREAKING CHANGE: WorkerProxy credentials parameter type changed from
ChannelCredentialsType to WorkerCredentials | None | UndefinedType.
WorkerPool credentials parameter type changed from
WorkerCredentials | None | UndefinedType to WorkerCredentials | None.
ChannelCredentialsType and resolve_channel_credentials removed.

#77)

Define a RuntimeContext message with a dispatch_timeout field and add
it as an optional submessage on Task (field 11). The optional qualifier
enables HasField checks so workers can distinguish absent context
(older clients) from context with default values. Re-export the new
RuntimeContext type from the protocol package.

RuntimeContext gains to_protobuf/from_protobuf methods that serialize
the wire-safe subset of the context (dispatch_timeout only; credentials
are TLS material and intentionally excluded). The proto default 0.0
maps to None in Python.

Task gains a context field captured automatically in __post_init__ via
RuntimeContext.get_current(). The field is serialized as an optional
submessage on the wire Task and deserialized with a HasField check for
backward compatibility with older clients.

_run() and _stream() now enter self.context as a context manager before
calling the user's function, restoring dispatch_timeout into the
ContextVar so nested dispatch respects the original timeout. The
existing __enter__/__exit__ token machinery on RuntimeContext ensures
sequential tasks on the same worker loop do not leak state.

…pagation

Cover RuntimeContext.to_protobuf/from_protobuf with example-based and
property-based (Hypothesis) roundtrip tests. Cover Task context capture
in __post_init__, protobuf roundtrip with context submessage, backward
compatibility for messages without context, and dispatch_timeout
restoration in both _run() and _stream() including sequential task
isolation.

…Closes #69 (#72)

The context manager protocol (__enter__/__exit__) and the current()
classmethod on WorkerCredentials existed solely for internal ContextVar
propagation in worker subprocesses.  Exposing them publicly invited
misuse where users could override credentials outside of WorkerPool,
causing silent divergence between pool-configured and ContextVar
credentials.

Introduce _CredentialContext — an internal helper that owns the
ContextVar lifecycle — and strip the CM protocol, current(), and
the _token field from WorkerCredentials.  Update WorkerProcess._serve()
and WorkerProxy.__init__() to use the new helper.

…t internal — Closes #78 (#79)