Metadata-Version: 2.4
Name: lazily
Version: 0.31.0
Summary: A library for lazy evaluation with context caching
Author-email: Brian Takita <brian.takita@gmail.com>
Maintainer-email: Brian Takita <brian.takita@gmail.com>
License:                                  Apache License
                                   Version 2.0, January 2004
                                http://www.apache.org/licenses/
        
           TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
        
           1. Definitions.
        
              "License" shall mean the terms and conditions for use, reproduction,
              and distribution as defined by Sections 1 through 9 of this document.
        
              "Licensor" shall mean the copyright owner or entity authorized by
              the copyright owner that is granting the License.
        
              "Legal Entity" shall mean the union of the acting entity and all
              other entities that control, are controlled by, or are under common
              control with that entity. For the purposes of this definition,
              "control" means (i) the power, direct or indirect, to cause the
              direction or management of such entity, whether by contract or
              otherwise, or (ii) ownership of fifty percent (50%) or more of the
              outstanding shares, or (iii) beneficial ownership of such entity.
        
              "You" (or "Your") shall mean an individual or Legal Entity
              exercising permissions granted by this License.
        
              "Source" form shall mean the preferred form for making modifications,
              including but not limited to software source code, documentation
              source, and configuration files.
        
              "Object" form shall mean any form resulting from mechanical
              transformation or translation of a Source form, including but
              not limited to compiled object code, generated documentation,
              and conversions to other media types.
        
              "Work" shall mean the work of authorship, whether in Source or
              Object form, made available under the License, as indicated by a
              copyright notice that is included in or attached to the work
              (an example is provided in the Appendix below).
        
              "Derivative Works" shall mean any work, whether in Source or Object
              form, that is based on (or derived from) the Work and for which the
              editorial revisions, annotations, elaborations, or other modifications
              represent, as a whole, an original work of authorship. For the purposes
              of this License, Derivative Works shall not include works that remain
              separable from, or merely link (or bind by name) to the interfaces of,
              the Work and Derivative Works thereof.
        
              "Contribution" shall mean any work of authorship, including
              the original version of the Work and any modifications or additions
              to that Work or Derivative Works thereof, that is intentionally
              submitted to Licensor for inclusion in the Work by the copyright owner
              or by an individual or Legal Entity authorized to submit on behalf of
              the copyright owner. For the purposes of this definition, "submitted"
              means any form of electronic, verbal, or written communication sent
              to the Licensor or its representatives, including but not limited to
              communication on electronic mailing lists, source code control systems,
              and issue tracking systems that are managed by, or on behalf of, the
              Licensor for the purpose of discussing and improving the Work, but
              excluding communication that is conspicuously marked or otherwise
              designated in writing by the copyright owner as "Not a Contribution."
        
              "Contributor" shall mean Licensor and any individual or Legal Entity
              on behalf of whom a Contribution has been received by Licensor and
              subsequently incorporated within the Work.
        
           2. Grant of Copyright License. Subject to the terms and conditions of
              this License, each Contributor hereby grants to You a perpetual,
              worldwide, non-exclusive, no-charge, royalty-free, irrevocable
              copyright license to reproduce, prepare Derivative Works of,
              publicly display, publicly perform, sublicense, and distribute the
              Work and such Derivative Works in Source or Object form.
        
           3. Grant of Patent License. Subject to the terms and conditions of
              this License, each Contributor hereby grants to You a perpetual,
              worldwide, non-exclusive, no-charge, royalty-free, irrevocable
              (except as stated in this section) patent license to make, have made,
              use, offer to sell, sell, import, and otherwise transfer the Work,
              where such license applies only to those patent claims licensable
              by such Contributor that are necessarily infringed by their
              Contribution(s) alone or by combination of their Contribution(s)
              with the Work to which such Contribution(s) was submitted. If You
              institute patent litigation against any entity (including a
              cross-claim or counterclaim in a lawsuit) alleging that the Work
              or a Contribution incorporated within the Work constitutes direct
              or contributory patent infringement, then any patent licenses
              granted to You under this License for that Work shall terminate
              as of the date such litigation is filed.
        
           4. Redistribution. You may reproduce and distribute copies of the
              Work or Derivative Works thereof in any medium, with or without
              modifications, and in Source or Object form, provided that You
              meet the following conditions:
        
              (a) You must give any other recipients of the Work or
                  Derivative Works a copy of this License; and
        
              (b) You must cause any modified files to carry prominent notices
                  stating that You changed the files; and
        
              (c) You must retain, in the Source form of any Derivative Works
                  that You distribute, all copyright, patent, trademark, and
                  attribution notices from the Source form of the Work,
                  excluding those notices that do not pertain to any part of
                  the Derivative Works; and
        
              (d) If the Work includes a "NOTICE" text file as part of its
                  distribution, then any Derivative Works that You distribute must
                  include a readable copy of the attribution notices contained
                  within such NOTICE file, excluding those notices that do not
                  pertain to any part of the Derivative Works, in at least one
                  of the following places: within a NOTICE text file distributed
                  as part of the Derivative Works; within the Source form or
                  documentation, if provided along with the Derivative Works; or,
                  within a display generated by the Derivative Works, if and
                  wherever such third-party notices normally appear. The contents
                  of the NOTICE file are for informational purposes only and
                  do not modify the License. You may add Your own attribution
                  notices within Derivative Works that You distribute, alongside
                  or as an addendum to the NOTICE text from the Work, provided
                  that such additional attribution notices cannot be construed
                  as modifying the License.
        
              You may add Your own copyright statement to Your modifications and
              may provide additional or different license terms and conditions
              for use, reproduction, or distribution of Your modifications, or
              for any such Derivative Works as a whole, provided Your use,
              reproduction, and distribution of the Work otherwise complies with
              the conditions stated in this License.
        
           5. Submission of Contributions. Unless You explicitly state otherwise,
              any Contribution intentionally submitted for inclusion in the Work
              by You to the Licensor shall be under the terms and conditions of
              this License, without any additional terms or conditions.
              Notwithstanding the above, nothing herein shall supersede or modify
              the terms of any separate license agreement you may have executed
              with Licensor regarding such Contributions.
        
           6. Trademarks. This License does not grant permission to use the trade
              names, trademarks, service marks, or product names of the Licensor,
              except as required for reasonable and customary use in describing the
              origin of the Work and reproducing the content of the NOTICE file.
        
           7. Disclaimer of Warranty. Unless required by applicable law or
              agreed to in writing, Licensor provides the Work (and each
              Contributor provides its Contributions) on an "AS IS" BASIS,
              WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
              implied, including, without limitation, any warranties or conditions
              of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A
              PARTICULAR PURPOSE. You are solely responsible for determining the
              appropriateness of using or redistributing the Work and assume any
              risks associated with Your exercise of permissions under this License.
        
           8. Limitation of Liability. In no event and under no legal theory,
              whether in tort (including negligence), contract, or otherwise,
              unless required by applicable law (such as deliberate and grossly
              negligent acts) or agreed to in writing, shall any Contributor be
              liable to You for damages, including any direct, indirect, special,
              incidental, or consequential damages of any character arising as a
              result of this License or out of the use or inability to use the
              Work (including but not limited to damages for loss of goodwill,
              work stoppage, computer failure or malfunction, or any and all
              other commercial damages or losses), even if such Contributor
              has been advised of the possibility of such damages.
        
           9. Accepting Warranty or Additional Liability. While redistributing
              the Work or Derivative Works thereof, You may choose to offer,
              and charge a fee for, acceptance of support, warranty, indemnity,
              or other liability obligations and/or rights consistent with this
              License. However, in accepting such obligations, You may act only
              on Your own behalf and on Your sole responsibility, not on behalf
              of any other Contributor, and only if You agree to indemnify,
              defend, and hold each Contributor harmless for any liability
              incurred by, or claims asserted against, such Contributor by reason
              of your accepting any such warranty or additional liability.
        
           END OF TERMS AND CONDITIONS
        
           APPENDIX: How to apply the Apache License to your work.
        
              To apply the Apache License to your work, attach the following
              boilerplate notice, with the fields enclosed by brackets "[]"
              replaced with your own identifying information. (Don't include
              the brackets!)  The text should be enclosed in the appropriate
              comment syntax for the file format. We also recommend that a
              file or class name and description of purpose be included on the
              same "printed page" as the copyright notice for easier
              identification within third-party archives.
        
           Copyright [yyyy] [name of copyright owner]
        
           Licensed under the Apache License, Version 2.0 (the "License");
           you may not use this file except in compliance with the License.
           You may obtain a copy of the License at
        
               http://www.apache.org/licenses/LICENSE-2.0
        
           Unless required by applicable law or agreed to in writing, software
           distributed under the License is distributed on an "AS IS" BASIS,
           WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
           See the License for the specific language governing permissions and
           limitations under the License.
        
Project-URL: Homepage, https://github.com/lazily-hub/lazily-py
Project-URL: Bug Reports, https://github.com/lazily-hub/lazily-py/issues
Project-URL: Source, https://github.com/lazily-hub/lazily-py
Keywords: lazy,evaluation,dependency,injection,context,lazily
Classifier: Development Status :: 3 - Alpha
Classifier: Intended Audience :: Developers
Classifier: License :: OSI Approved :: Apache Software License
Classifier: Programming Language :: Python :: 3
Classifier: Programming Language :: Python :: 3.12
Classifier: Programming Language :: Python :: 3.13
Classifier: Programming Language :: Python :: 3.14
Classifier: Topic :: Software Development :: Libraries :: Python Modules
Classifier: Topic :: Utilities
Requires-Python: >=3.12
Description-Content-Type: text/markdown
License-File: LICENSE
Requires-Dist: mypy-extensions>=1.0
Provides-Extra: dev
Requires-Dist: build==1.4.0; extra == "dev"
Requires-Dist: jsonschema==4.23.0; extra == "dev"
Requires-Dist: mypy[mypyc]>=2.3; extra == "dev"
Requires-Dist: poethepoet==0.40.0; extra == "dev"
Requires-Dist: pytest-cov==7.0.0; extra == "dev"
Requires-Dist: pytest==9.0.2; extra == "dev"
Requires-Dist: referencing==0.37.0; extra == "dev"
Requires-Dist: ruff==0.14.14; extra == "dev"
Requires-Dist: twine==6.2.0; extra == "dev"
Requires-Dist: ty==0.0.14; extra == "dev"
Dynamic: license-file

# lazily

Lazy reactive primitives for Python — Slots, Cells, and Signals with automatic
dependency tracking and cache invalidation, plus the language-agnostic
`lazily-spec` wire protocol for mirroring graph state across processes and
languages.

[![PyPI](https://img.shields.io/pypi/v/lazily.svg)](https://pypi.org/project/lazily/)

## Overview

`lazily` provides a small reactive family for context-aware computation:

- **Slot** — a lazily-computed cached value that automatically tracks its dependencies (`slot` / `slot_def`).
- **Cell** — a mutable value that invalidates dependent Slots when it changes (`cell` / `cell_def`, `Cell`, `CellSlot`).
- **Signal** — an *eager* derived value that recomputes the instant a dependency invalidates, with no intermediate unset value (`signal` / `signal_def`).

Values are **lazy by default**: dependents are marked dirty on invalidation but
only recompute when accessed. When you need eager push-style semantics —
recompute immediately, observe `v1 → v2` with no unset window — reach for
**`Signal`**, which layers a puller over a memoized Slot. The
`Slot → Cell → Signal` progression lets you choose lazy or eager per derived
value within one graph. An equal recompute is suppressed by a `PartialEq`/memo
guard, so unchanged values never cascade downstream work.

There is **no dedicated `Context` class** — a plain `dict` is the context. Slots
use themselves as dictionary keys to cache values, so any dict works as the
reactive "world."

## Feature coverage

The full `lazily` capability set across every binding. Legend: ✅ shipped ·
`~` partial · `—` absent or not applicable. The canonical matrix with per-cell
notes and platform carve-outs lives in
[`lazily-spec` § Cross-Language Coverage](https://github.com/lazily-hub/lazily-spec/blob/main/docs/coverage.md).

<!-- coverage-table:start -->
| Feature | Rust | Python | Kotlin | JS | Dart | Zig | Go | C++ |
| --------- | :----: | :------: | :------: | :--: | :----: | :---: | :--: | :---: |
| Reactive graph — core `Cell` / `Slot` / `Effect` (+ derived `Signal` = `Slot.eager`) / memo / batch | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| Keyed-map materialization (`SlotMap`) — mint-on-access derived slots: transparency + deferral (`#lzmatmode`) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| Thread-safe keyed map (`ThreadSafeSlotMap`) — `Send + Sync` + materialization confluence (`#lzmatmode`) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| Async keyed map (`AsyncSlotMap`) — eventual transparency (`#lzmatmode`) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| Keyed-map sync — membership propagation + materialize-on-ingest + derived-aggregate transparency (`#lzfamilysync`) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| Thread-safe context (lock-backed) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| Async reactive context | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| Flat state machine | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| Harel state charts | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| Keyed reactive maps (`ReactiveMap`: `CellMap` / `SlotMap`) + `CellTree` + reconcile | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| Memoized semantic tree (`SemTree`) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| Stable-id alignment (manufactured identity) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| Reactive queue (`QueueCell` SPSC/MPSC + `QueueStorage` adapter) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| Broadcast topic (`TopicCell`) — independent cursors + durable replay + safe GC (`#lztopiccell`) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| Competing-consumer work queue (`WorkQueueCell`) — exclusive leases + ack/nack + redelivery + DLQ (`#lzworkqueue`) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| Merge algebra + `MergeCell` — associative `MergePolicy` (`KeepLatest`/`Sum`/`Max`/`SetUnion`/`RawFifo`), `Cell ≡ MergeCell<KeepLatest>`, `Reactive`/`Source` split (`#relaycell`) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| RelayCell — conflating relay + `BackpressurePolicy` + `SpillStore` + `Transport` + Inbox/Outbox + Rate/Window/Expiry/Priority/keyed policies (`#relaycell`) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| Free-text character CRDT (`TextCrdt`) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| `TextCrdt` delta sync (`version_vector` / `delta_since` / `apply_delta`) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| `CrdtTree` lossless document contract (`#lzcrdttree`) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| Move-aware sequence CRDT (`SeqCrdt`) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| Lossless tree CRDT core (`LosslessTreeCrdt`, M1) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| Lossless tree — dotted-frontier anti-entropy | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| Lossless tree — concurrent merge convergence | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| Registers (LWW / MV) + `PnCounter` + `CellCrdt` | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| IPC wire — `Snapshot` + `Delta` + `CrdtSync` | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| Shared-memory blob path (`ShmBlobArena`) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| Cross-process zero-copy transport (`BlobBackend` / shm / arrow) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| Distributed CRDT plane (`CrdtPlaneRuntime` / anti-entropy) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| Reliable sync — resync coordinator + at-least-once durable outbox + OR-set/LWW liveness (`#lzsync`) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| Storage-independent durable outbox (`OutboxStore` + shared outbox protocol; SQLite/Room/IndexedDB/file adapters) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| Reliable-sync transport seam + full-duplex `SyncDriver` loop (`IpcSink`/`IpcSource`, `#sync-driver`) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| Distributed plane — WebRTC transport + signaling | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| State projection / mirror | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| Causal receipts (`CausalReceipts` outcome projection) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| Message-passing + RPC command plane (`command-plane-v1`) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| C-ABI FFI boundary | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| Permission boundary (`PeerPermissions` / `RemoteOp`) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| Capability negotiation (`SessionHandshake`) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| Instrumentation / benchmarks | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| Temporal sources — `TimerCell` / `IntervalCell` / `CronCell` / `DeadlineCell` over a logical clock (`#lztime`) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| Rate-shaping operators — `DebounceCell` / `ThrottleCell` / `SampleCell` / `ProbabilisticSampleCell` (`#lzrateshape`) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| Membership + failure detection — `MembershipCell` (SWIM + Phi-accrual) / `PeerSet` / `PeerChangeEvent` (`#lzmemb`) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| Distributed coordination — `LeaseCell` / `LeaderCell` / `LockCell` / `SemaphoreCell` / `BarrierCell`+`QuorumCell` (`#lzcoord`) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| Presence + ephemeral plane — `PresenceCell` / `AwarenessCell` / `EphemeralCell` + `Ephemeral`/`Durable` markers (`#lzpresence`) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| Stream windowing — `TumblingWindow` / `SlidingWindow` / `SessionWindow` over the merge algebra (`#lzwindow`) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| Fault tolerance — `CircuitBreakerCell` / `RetryPolicyCell` / `BulkheadCell` / `TimeoutCell` (`#lzresilience`) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| Embedded-service plane — `HealthCell` / `ReadinessCell` / `DiscoveryCell` / `ServiceRegistry` (`#lzservice`) | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
<!-- coverage-table:end -->

## Installation

```
pip install lazily
```

## Example usage

```python
from lazily import CellSlot, cell, slot

# Cells hold a value that can be updated.
name = CellSlot[dict, dict, str]()


# Slots are functions that depend on cells and other slots.
@slot
def greeting(ctx: dict) -> str:
    print("Calculating greeting...")
    return f"Hello, {name(ctx).value}!"


# A CellSlot can also have a default value.
@cell
def response(ctx: dict) -> str:
    return "How are you?"


@slot
def greeting_and_response(ctx: dict) -> str:
    print("Calculating greeting_and_response...")
    return f"{greeting(ctx)} {response(ctx).value}"


ctx = {}

name(ctx).value = "World"

# First access: runs the function
print(greeting(ctx))
# Calculating greeting...
# 'Hello, World!'

# Second access: uses cache (no print)
print(greeting(ctx))
# 'Hello, World!'

# Dependencies also access cached values
print(greeting_and_response(ctx))
# Calculating greeting_and_response...
# 'Hello, World! How are you?'

# Dependencies also cached
print(greeting_and_response(ctx))
# 'Hello, World! How are you?'

# Update cell: invalidates cache
name(ctx).value = "Lazily"

# Access again: re-runs the function
print(greeting_and_response(ctx))
# Calculating greeting_and_response...
# Calculating greeting...
# 'Hello, Lazily! How are you?'

# Another access: uses cache
print(greeting_and_response(ctx))
# 'Hello, Lazily! How are you?'
```

## Core Concepts

### Context

A plain `dict` is the context. It owns all cached Slot values; Slots store their
cache under themselves as keys. The current implementation is single-threaded —
create one dict per reactive graph.

### Slot

A Slot wraps a compute function `(ctx) -> T`; the result is cached after first
access. Dependencies are discovered automatically via a global `slot_stack` —
any Slot or Cell read during computation becomes a dependency and re-subscribes
on every recompute, so conditional branches update the dependency graph with no
manual cleanup. When a dependency invalidates, the Slot only marks its cache
dirty; it does **not** recompute until called again.

| Type | Purpose |
|------|---------|
| `BaseSlot[C_in, C_ctx, T]` | Base slot without subscriber support |
| `Slot[C_in, C_ctx, T]` | Slot with dependency tracking and invalidation |
| `slot` | Decorator: `Slot` with an identity context resolver |
| `slot_def(resolve_ctx)` | Decorator factory for a custom context resolver |

### Cell

A `Cell` holds a mutable value. Reading `cell.value` inside a Slot auto-subscribes
that Slot; assigning `cell.value = x` (or `cell.set(x)`) compares old and new via
`!=` and, only if changed, cascades invalidation to dependents.

| Type | Purpose |
|------|---------|
| `Cell[T]` | Mutable value with subscription support |
| `CellSlot[C_in, C_ctx, T]` | Slot that returns a `Cell` |
| `cell` | Decorator: `CellSlot` with an identity resolver |
| `cell_def(resolve_ctx)` | Decorator factory for a custom context resolver |

### Signal

A `Signal` is the **eager** counterpart to a lazy Slot — one step further along
the `Slot → Cell → Signal` progression. Where a Slot marks itself dirty on
invalidation and recomputes on the next read, a Signal recomputes *the instant a
dependency is invalidated*, before the mutating call returns. The value is always
materialized, so observers never see an intermediate unset value.

```python
from lazily import CellSlot, signal

n = CellSlot[dict, dict, int]()


@signal
def doubled(ctx: dict) -> int:
    return n(ctx).value * 2


ctx: dict = {}
n(ctx).value = 1

s = doubled(ctx)   # eager: materialized now
print(s.value)     # 2

n(ctx).value = 5   # doubled recomputes immediately
print(s.value)     # 10 — already current, no lazy read needed
```

A Signal is **composed from existing primitives**, not a parallel engine: a
memoized Slot supplies glitch-free, memo-guarded recomputation, and a small
puller re-materializes it after every invalidation to supply the eagerness.
Consequently a Signal inherits the memo guard (an equal recompute suppresses the
downstream cascade). `signal.dispose()` removes the eager puller — the value
stays readable but reverts to lazy (recompute-on-read) behavior.

| Type | Purpose |
|------|---------|
| `Signal[T]` | Eager derived value bound to a single context |
| `signal` | Decorator: context-cached eager-Signal factory (one Signal per context) |
| `signal_def(resolve_ctx)` | Decorator factory with a custom context resolver |

### StateMachine

`StateMachine[S, E]` is a finite state machine backed by a reactive `Cell`, so
its `state` participates in dependency tracking like any other reactive value.
Construct it with `StateMachine(ctx, initial, transition)` where `transition` is
a pure `(state, event) -> next_state | None` (returning `None` rejects the
event). `send(event)` returns whether the transition was accepted; a
self-transition to an equal state is accepted but suppressed by the Cell's
`PartialEq` guard.

### Reactive collections, async, and thread-safe contexts

lazily-py also implements the `lazily-spec` compute-layer `MUST`s, each ported
from its Lean formal model in [`lazily-formal`](https://github.com/lazily-hub/lazily-formal):

- **`ReactiveMap` / `CellMap` / `SlotMap` / `CellTree`** — keyed reactive
  collections (`#reactivemap`) with independent value/membership/order signals and
  atomic move. One generic `ReactiveMap` over a handle kind; `CellMap` (input
  cells, adds `set` + eager `entry`) and `SlotMap` (derived slots, lazy
  `get_or_insert_with` + eager `materialize_all`) are its specializations.
- **`QueueCell`** — a reactive FIFO queue (SPSC primitive with an MPSC-via-`batch`
  usage rule) with a pluggable `QueueStorage` backend. Reader-kind invalidation
  (head/len/is_empty/is_full/closed), bounded reactive backpressure via `is_full`,
  and the closure lifecycle (drain / Closed-distinct-from-Empty / idempotent).
- **`reconcile_ops`** — move-minimized keyed reconciliation (LIS kernel).
- **`AsyncSlot` / `AsyncEffect`** — the async slot lifecycle with stale-completion
  discard, and cleanup-before-body effect scheduling.
- **`ThreadSafeContext`** — a lock-serialized `batch` boundary that coalesces
  writes into one invalidation pass.
- **`lazily.ffi`** — the C-ABI FFI boundary (`LazilyFfiStatus`,
  `LazilyFfiMessageKind` incl. `CrdtSync = 3`, `LazilyFfiBytes`).

The test suite gates on `lazily-formal`'s `lake build` (every theorem checks)
and mirrors the named Lean theorems as property tests. See `SPEC.md` for the
full compliance surface.

## Reactive queue — `lazily.queue`

`QueueCell` is a FIFO collection composed of reactive cells — **not a new cell
kind** — that adds queue semantics (push to tail, pop from head) to the reactive
graph. It is an SPSC primitive; MPSC is a *usage rule* on the same primitive —
multiple producers push inside one `batch`, which serializes the pushes into a
deterministic order. The reactive shell wraps a pluggable `QueueStorage` backend
(default `VecDequeStorage`); the shell owns the reader-kind version cells and
invalidates by reader kind — a push to a non-empty queue does NOT invalidate the
`head` reader, a pop does.

```python
from lazily import QueueCell, QueuePopError, batch

ctx = {}
q: QueueCell[str] = QueueCell(ctx)

q.try_push("a")
q.try_push("b")
assert q.head() == "a"
assert q.len() == 2
assert q.try_pop() == "a"

# Bounded queue → reactive backpressure via is_full.
bq = QueueCell[int].with_capacity(ctx, 2)
bq.try_push(1)
bq.try_push(2)
assert bq.is_full()
assert bq.try_push(3).label == "Full"   # reject at capacity
assert bq.try_pop() == 1
assert not bq.is_full()                  # pop freed a slot → is_full reader invalidated

# MPSC: multiple producers push inside one batch → one invalidation pass.
batch(lambda: (q.try_push("p1"), q.try_push("p2")))

# Closure: pop on closed+empty returns Closed (distinct from Empty).
q.close()
assert q.is_closed()
assert q.try_push("x").label == "Closed"
```

### Competing-consumer work queue

`WorkQueueCell` provides exclusive FIFO claims with visibility deadlines,
worker-scoped acknowledgements, tail retries, and bounded dead-letter handling.
Item ids survive retries while each claim gets a fresh delivery id.

```python
from lazily import WorkQueueCell

work = WorkQueueCell[str](ctx, visibility_timeout=10, max_deliveries=3)
work.push("job")
delivery = work.claim("worker-a", 100)
assert delivery is not None
assert work.ack("worker-a", delivery.delivery_id)
```

The reader-kind independence law (a push to a non-empty queue does not change
`head`, so the `head` reader is not invalidated) comes for free from the Cell
`!=` (PartialEq) guard: after each op the shell re-derives each reader-kind cell
from storage and writes it back, and a cell whose value did not change is not
invalidated.

## IPC — the `lazily-spec` wire protocol

`lazily.ipc` implements the language-agnostic [`lazily-spec`](https://github.com/lazily-hub/lazily-spec)
wire protocol, so a Python graph's state can be mirrored to remote observers
across processes and languages. The JSON encoding is **byte-compatible** with the
Rust (`lazily-rs`), Zig (`lazily-zig`), and TypeScript (`@lazily/signaling`)
bindings, and is validated against the canonical `lazily-spec/conformance`
fixtures (vendored under `tests/conformance/`).

Two message kinds flow over any transport (WebSocket text, WebRTC data, FFI
buffer):

- **`Snapshot`** — the full graph state at an epoch (`nodes`, `edges`, `roots`).
- **`Delta`** — an ordered batch of the 7 `DeltaOp` variants (`CellSet`,
  `SlotValue`, `Invalidate`, `NodeAdd`, `NodeRemove`, `EdgeAdd`, `EdgeRemove`)
  applied with epoch sequencing and fail-closed resync.

```python
from lazily import (
    Snapshot, NodeSnapshot, EdgeSnapshot, ShmBlobRef,
    Delta, DeltaOp, IpcMessage,
)

# Build and serialize a snapshot — encode_json() returns transport-agnostic bytes.
snap = Snapshot(
    epoch=7,
    nodes=[
        NodeSnapshot.payload(1, "i32", bytes([1, 2, 3])),
        NodeSnapshot.opaque(2, "opaque-type"),
        NodeSnapshot.shared_blob(3, "text/plain", ShmBlobRef(0, 16, 1, 7, 999)),
    ],
    edges=[EdgeSnapshot(2, 1), EdgeSnapshot(3, 1)],
    roots=[1, 2],
)
wire = IpcMessage.of_snapshot(snap).encode_json()
assert IpcMessage.decode_json(wire).snapshot == snap

# An incremental delta carrying mutations.
delta = Delta.next(40, [
    DeltaOp.cell_set(1, bytes([10])),
    DeltaOp.invalidate(3),
])
IpcMessage.of_delta(delta).encode_json()
```

A `PeerPermissions` boundary gates what is shared: it is **default-deny**, so only
nodes a peer is explicitly allowed to read are serialized into a snapshot or
delta — non-allowlisted nodes are omitted entirely.

### Shared-memory blobs — `ShmBlobArena`

`ShmBlobArena` lets a Python process **host** blob payloads (not just carry
`ShmBlobRef` descriptors). It is a `bytearray`-backed, append-only arena with a
40-byte header (`LZSH` magic + FNV-1a-64 checksum) and wraparound, ported from
the `lazily-rs` `ShmBlobArena<B>` and byte-compatible with the Rust and Zig
arenas. The module exports `ShmBlobArena`, `ShmBlobArenaError` (with its variant
subclasses), and `SHM_BLOB_HEADER_LEN`.

## Lossless tree CRDT — `lazily.lossless_tree_crdt`

`LosslessTreeCrdt` (#lzlosstree) is a single rooted concrete-syntax tree whose
**leaves own every rendered byte** — `render(tree) == source_text` for valid,
invalid, and unknown source alike. Where `TextCrdt` is a flat lossless floor,
this is the structured tree that can itself be the wire authority. Element nodes
own structure only; all text lives in leaf nodes tagged `Token` / `Trivia` /
`Raw` / `Error`, so unknown/invalid spans round-trip exactly as `Raw`/`Error`
leaves rather than being discarded.

```python
from lazily import LeafKind, LosslessTreeCrdt, SeedElement, SeedLeaf
from lazily.lossless_tree_crdt import ROOT

tree = LosslessTreeCrdt(peer=1)
heading = tree.create_node(ROOT, None, SeedElement("heading"))
tree.create_node(heading, None, SeedLeaf(LeafKind.TOKEN, "# "))
title = tree.create_node(heading, None, SeedLeaf(LeafKind.RAW, "Título"))
assert tree.render() == "# Título"

# Op-based delta sync: fork, diverge, converge through a dotted frontier.
other = tree.fork(peer=2)
other.edit_leaf(title, 0, 0, "X")
tree.apply_update(other.diff(tree.frontier()))
assert tree.render() == other.render()
```

Leaf text embeds `TextCrdt` wholesale; child order is a fractional index
(`key_between`); the clock is a Lamport `TreeOpId`. Anti-entropy is op-based over
a **dotted, non-contiguous version frontier** (`TreeVersionFrontier`) — a dot
*set* (contiguous prefix + sparse holes), never a per-peer max, so a missing
interior op stays representable and re-requestable. Leaf-local wire offsets are
UTF-8 bytes (`byte_to_char`). The wire codec (`tree_update_to_wire` /
`tree_update_from_wire`) validates against `lazily-spec`'s
`lossless-tree-delta.json`, and all nine `conformance/lossless-tree/` fixtures
replay.

## Command / RPC message plane — `lazily.command`

`command-plane-v1` is an **additive sibling** to `Snapshot` / `Delta` /
`CrdtSync`: four evented frames (`CommandSubmit` / `CommandCancel` /
`CommandEvents` / `CommandProjection`) that carry command traffic, not cell
state. lazily owns the envelope; the namespace owns the `IpcValue` payload, which
lazily never decodes.

The single hard rule: **terminal authority is the causal receipt.** A command is
terminal only when a terminal `CausalReceipt` for its `command_id` folds in
(`applied`, or `rejected` — including the `cancelled` / `superseded` /
`timed_out` reasons). `observed` / `accepted` / `started` events are progress
only; a transport ACK is never terminal.

```python
from lazily import (
    CommandPolicy, CommandRpcClient, CommandSubmit, DedupePolicy,
    applied_receipt,
)
from lazily.ipc import IpcValue

class Transport:
    def __init__(self):
        self.sent = []

    def send(self, message):
        self.sent.append(message)

client = CommandRpcClient(Transport())
cmd_id = client.submit(CommandSubmit(
    command_id="cmd-1", causation_id="cmd-1", source="plugin",
    target="controller", namespace="agent-doc", name="editor_route",
    authority_generation=1, idempotency_key="doc:run", deadline_ms=0,
    policy=CommandPolicy(DedupePolicy.SAME_IDEMPOTENCY_KEY, False, True),
    payload_type="agent-doc.editor_route.v1", payload_hash="sha256:…",
    payload=IpcValue.of(b"{…}"),
    required_features=["command-plane-v1"],
))
# `call` resolves ONLY on a terminal receipt — never an ACK or `accepted`.
client.ingest_receipt(applied_receipt("rcpt-1", cmd_id, "controller", 1))
assert client.poll_call(cmd_id).kind.value == "resolved"
```

`CommandProjection` is the pure reducer (generation guards, idempotency,
cancel-before-terminal-only, terminal-conflict-fails-closed, reconnect
equivalence); `CommandRpcClient` is the derived RPC facade. The wire codec
validates against `lazily-spec`'s `message-passing.json`, and all eight
`conformance/message-passing/` fixtures replay.

## Benchmarks

Wall-clock benchmarks live in [`BENCHMARKS.md`](BENCHMARKS.md), covering both
the in-library micro-suite (reactive core, keyed reconciliation, `CellMap`,
`TextCrdt`, CRDT plane) and a large spreadsheet-shaped **scale** suite that
mirrors the lazily-rs / lazily-go `scale` groups (`N` input cells + `N` formula
slots, `formula[i] = input[i] + input[i-1]`). The scale suite is measured up to
a full **10,000,000-cell Google Sheets workbook** (`N = 5,000,000`); a one-cell
edit plus a 1,000-cell viewport read stays in the ~75 µs range regardless of
sheet size, because the lazy pull model recomputes only the ~2 formulas that
read the edited input.

```bash
make bench          # micro-suite
make bench-scale    # scale suite (default N = 1,000,000)

# or directly, with a custom size:
uv run python -m lazily.benchmarks
LAZILY_SCALE_N=5000000 uv run python -m lazily.scale_bench   # 10M-cell workbook
```

See [`BENCHMARKS.md`](BENCHMARKS.md) for the full results, hardware, and honest
notes on CPython's per-node overhead.

## The lazily family

`lazily-py` is one binding in a cross-language reactive family that shares the
`lazily-spec` wire protocol:

| Binding | Language | Package |
|---------|----------|---------|
| [`lazily-rs`](https://github.com/lazily-hub/lazily-rs) | Rust | `lazily` (crates.io) |
| **`lazily-py`** | Python | `lazily` (PyPI) |
| [`lazily-zig`](https://github.com/lazily-hub/lazily-zig) | Zig | GitHub |
| [`@lazily/signaling`](https://github.com/lazily-hub/lazily-js) | TypeScript / Cloudflare Worker | npm |
| [`lazily-spec`](https://github.com/lazily-hub/lazily-spec) | — | wire protocol + conformance fixtures |
| [`lazily-formal`](https://github.com/lazily-hub/lazily-formal) | — | Lean 4 formal model (FSM kernel + Harel state chart) |

See [`lazily-spec`](https://github.com/lazily-hub/lazily-spec) for the canonical
Snapshot/Delta schemas, the IPC Lean proofs of the epoch/memo/batch invariants,
and the conformance fixtures every IPC-capable binding validates against. The
language-agnostic formal model — the flat FSM kernel and the full Harel state
chart — lives in [`lazily-formal`](https://github.com/lazily-hub/lazily-formal).

## Development

This project uses [`uv`](https://github.com/astral-sh/uv). Run the local
CI-equivalent suite — type-check (`ty`), lint (`ruff`), the runnable README
example, and the test suite — with:

```bash
uv run poe precommit
```

`SPEC.md` is the authoritative specification for the Python primitives and the
`lazily-spec` compliance notes.
