Add experimental typed chain API for tmux command sequences

CHANGES

@@ -45,6 +45,20 @@ $ uvx --from 'libtmux' --prerelease allow python
 _Notes on the upcoming release will go here._
 <!-- END PLACEHOLDER - ADD NEW CHANGELOG ENTRIES BELOW THIS LINE -->
 
+### What's new
+
+#### New: chainable tmux commands (`libtmux._experimental.chain`)
+
+Build a sequence of tmux commands and run it in a single tmux call,
+instead of one subprocess per command. References to panes, windows,
+and sessions can be lazy — point at an object a command will create
+and keep building against it — and they all resolve together when the
+chain runs. Experimental and opt-in: import from
+`libtmux._experimental.chain`, not the top-level `libtmux`.
+When callers need per-command output, the experimental control-mode
+runner batches command lines through one persistent `tmux -C` client
+and returns one result per command. (#685)
+
 ## libtmux 0.58.1 (2026-06-16)
 
 libtmux 0.58.1 restores compatibility with pytest 9.1. The bundled

docs/experiment/api/libtmux._experimental.chain._async.md

@@ -0,0 +1,13 @@
+# Async - `libtmux._experimental.chain._async`
+
+:::{warning}
+Experimental. This API is **not** covered by version policies and can break or
+be removed between minor versions.
+:::
+
+```{eval-rst}
+.. automodule:: libtmux._experimental.chain._async
+   :members:
+   :undoc-members:
+   :show-inheritance:
+```

docs/experiment/api/libtmux._experimental.chain._connection.md

@@ -0,0 +1,13 @@
+# Connecting to live tmux sessions - `libtmux._experimental.chain._connection`
+
+:::{warning}
+Experimental. This API is **not** covered by version policies and can break or
+be removed between minor versions.
+:::
+
+```{eval-rst}
+.. automodule:: libtmux._experimental.chain._connection
+   :members:
+   :undoc-members:
+   :show-inheritance:
+```

docs/experiment/api/libtmux._experimental.chain.chain.md

@@ -0,0 +1,13 @@
+# Chain - `libtmux._experimental.chain.chain`
+
+:::{warning}
+Experimental. This API is **not** covered by version policies and can break or
+be removed between minor versions.
+:::
+
+```{eval-rst}
+.. automodule:: libtmux._experimental.chain.chain
+   :members:
+   :undoc-members:
+   :show-inheritance:
+```

docs/experiment/api/libtmux._experimental.chain.control.md

@@ -0,0 +1,13 @@
+# Control mode - `libtmux._experimental.chain.control`
+
+:::{warning}
+Experimental. This API is **not** covered by version policies and can break or
+be removed between minor versions.
+:::
+
+```{eval-rst}
+.. automodule:: libtmux._experimental.chain.control
+   :members:
+   :undoc-members:
+   :show-inheritance:
+```

docs/experiment/api/libtmux._experimental.chain.ir.md

@@ -0,0 +1,13 @@
+# Intermediate representation - `libtmux._experimental.chain.ir`
+
+:::{warning}
+Experimental. This API is **not** covered by version policies and can break or
+be removed between minor versions.
+:::
+
+```{eval-rst}
+.. automodule:: libtmux._experimental.chain.ir
+   :members:
+   :undoc-members:
+   :show-inheritance:
+```

docs/experiment/api/libtmux._experimental.chain.plan.md

@@ -0,0 +1,13 @@
+# Expressions - `libtmux._experimental.chain.plan`
+
+:::{warning}
+Experimental. This API is **not** covered by version policies and can break or
+be removed between minor versions.
+:::
+
+```{eval-rst}
+.. automodule:: libtmux._experimental.chain.plan
+   :members:
+   :undoc-members:
+   :show-inheritance:
+```

docs/experiment/index.md

@@ -0,0 +1,195 @@
+(experimental)=
+
+# Experimental
+
+:::{danger}
+**No stability guarantee.** Everything under `libtmux._experimental` is **not**
+covered by the project's versioning policy. It can change or be removed between
+any releases without notice.
+
+These APIs are published so the design can be exercised and reviewed before any
+stability commitment. If you depend on something here and want it stabilized,
+please [file an issue](https://github.com/tmux-python/libtmux/issues).
+:::
+
+## Chainable commands
+
+`libtmux._experimental.chain` lets you build an ordered sequence of
+typed tmux commands that runs as **one** native `tmux ... \; ...` invocation,
+instead of one subprocess per command. The pieces layer up, so you can reach for
+as much or as little as you need:
+
+- **Intermediate representation** -- the typed argv layer beneath everything: a
+  {class}`~libtmux._experimental.chain.ir.CommandCall` is a single
+  command, and a
+  {class}`~libtmux._experimental.chain.ir.CommandChain` is an
+  ordered group that renders to one argv (with standalone `;` separators) and
+  dispatches once.
+- **Expressions** -- compose commands from a lazy, target-safe pane query. A
+  {class}`~libtmux._experimental.chain.plan.PaneQuery` resolves
+  against a pure
+  {class}`~libtmux._experimental.chain.plan.TmuxSnapshot`, maps each
+  typed row to commands, and compiles to one sequence -- so you can build and
+  assert the result without touching tmux.
+- **Async** -- {mod}`~libtmux._experimental.chain._async` mirrors the
+  same query and dispatch API with `await`, while command construction stays
+  synchronous and one expression still compiles to one invocation.
+- **Connecting to live tmux sessions** -- the bridge to a real server:
+  {func}`~libtmux._experimental.chain._connection.snapshot_from_session`
+  reads live panes, and
+  {class}`~libtmux._experimental.chain._connection.SessionPlanExecutor`
+  (with its async counterpart
+  {class}`~libtmux._experimental.chain._connection.AsyncSessionPlanExecutor`)
+  resolves and runs an expression against a live {class}`~libtmux.Session` in one
+  invocation.
+- **Control mode** --
+  {class}`~libtmux._experimental.chain.control.ControlModeRunner`
+  batches command lines through one persistent `tmux -C` client and returns one
+  result per command when callers need per-command output.
+- **Chainability** --
+  {mod}`~libtmux._experimental.chain.chain` decides which commands
+  may share one invocation: the static
+  {attr}`~libtmux._experimental.chain.ir.CommandSpec.chainable`
+  flag, plus a deferred result that won't hand back output until the chain has
+  run.
+
+::::{grid} 1 2 2 2
+:gutter: 2 2 3 3
+
+:::{grid-item-card} Intermediate representation
+:link: api/libtmux._experimental.chain.ir
+:link-type: doc
+The typed argv layer: `CommandCall`, `CommandChain`, `CommandSpec`.
+:::
+
+:::{grid-item-card} Expressions
+:link: api/libtmux._experimental.chain.plan
+:link-type: doc
+Build commands from a lazy, target-safe pane query.
+:::
+
+:::{grid-item-card} Async
+:link: api/libtmux._experimental.chain._async
+:link-type: doc
+The same query and dispatch API, with `await`.
+:::
+
+:::{grid-item-card} Connecting to live tmux sessions
+:link: api/libtmux._experimental.chain._connection
+:link-type: doc
+Read live panes and run an expression against a real session.
+:::
+
+:::{grid-item-card} Chainability
+:link: api/libtmux._experimental.chain.chain
+:link-type: doc
+Which commands may share one invocation.
+:::
+
+:::{grid-item-card} Control mode
+:link: api/libtmux._experimental.chain.control
+:link-type: doc
+Batch command lines with per-command results.
+:::
+
+::::
+
+## At a glance
+
+Compose typed calls and dispatch them as one tmux invocation:
+
+```python
+>>> from libtmux._experimental.chain.ir import CommandCall
+>>> sequence = (
+...     CommandCall("set-option", ("-g", "@cc_docs_a", "1"))
+...     >> CommandCall("set-option", ("-g", "@cc_docs_b", "2"))
+... )
+>>> sequence.argv()
+('set-option', '-g', '@cc_docs_a', '1', ';', 'set-option', '-g', '@cc_docs_b', '2')
+>>> sequence.run(session.server).returncode
+0
+>>> session.server.cmd("show-option", "-gv", "@cc_docs_b").stdout
+['2']
+```
+
+Build an expression from a query and compile it to one sequence -- pure, no tmux
+required:
+
+```python
+>>> from libtmux._experimental.chain.plan import (
+...     PaneRef,
+...     PaneTarget,
+...     SessionTarget,
+...     TmuxSnapshot,
+...     WindowTarget,
+...     panes,
+... )
+>>> snapshot = TmuxSnapshot(
+...     panes=(
+...         PaneRef.concrete(pane_id="%1", window_id="@1", session_id="$0",
+...                 pane_index=0, active=True, title="editor"),
+...         PaneRef.concrete(pane_id="%2", window_id="@1", session_id="$0",
+...                 pane_index=1, active=True, title="logs"),
+...     ),
+... )
+>>> plan = (
+...     panes()
+...     .filter(active=True)
+...     .order_by("pane_index")
+...     .commands(lambda pane: pane.cmd.resize_pane(height=20))
+... )
+>>> plan.to_chain(snapshot).argvs()
+(('resize-pane', '-t', '%1', '-y', '20'), ('resize-pane', '-t', '%2', '-y', '20'))
+```
+
+Against a live server, run the same expression in one invocation with
+{class}`~libtmux._experimental.chain._connection.SessionPlanExecutor`:
+
+```python
+>>> from libtmux._experimental.chain import SessionPlanExecutor, panes
+>>> runner = SessionPlanExecutor(session)
+>>> live_plan = panes().filter(active=True).commands(
+...     lambda pane: pane.cmd.send_keys("echo libtmux", enter=True),
+... )
+>>> live_plan.run(runner)
+```
+
+The same expression can be built and compiled asynchronously -- construction
+stays synchronous; only resolution and dispatch await:
+
+```python
+>>> import asyncio
+>>> from libtmux._experimental.chain import aio
+>>> from libtmux._experimental.chain.plan import (
+...     PaneRef,
+...     PaneTarget,
+...     SessionTarget,
+...     TmuxSnapshot,
+...     WindowTarget,
+... )
+>>> snapshot = TmuxSnapshot(
+...     panes=(
+...         PaneRef.concrete(pane_id="%1", window_id="@1", session_id="$0",
+...                 pane_index=0, active=True, title="editor"),
+...     ),
+... )
+>>> async def _resize() -> tuple[tuple[str, ...], ...]:
+...     plan = aio.panes().filter(active=True).commands(
+...         lambda pane: pane.cmd.resize_pane(height=20),
+...     )
+...     return (await plan.to_chain(snapshot)).argvs()
+>>> asyncio.run(_resize())
+(('resize-pane', '-t', '%1', '-y', '20'),)
+```
+
+```{toctree}
+:hidden:
+:maxdepth: 1
+
+api/libtmux._experimental.chain.ir
+api/libtmux._experimental.chain.plan
+api/libtmux._experimental.chain._async
+api/libtmux._experimental.chain._connection
+api/libtmux._experimental.chain.chain
+api/libtmux._experimental.chain.control
+```

docs/index.md

@@ -101,6 +101,7 @@ topics/index
 api/index
 api/testing/index
 internals/index
+experiment/index
 project/index
 history
 migration

docs/project/public-api.md

@@ -29,12 +29,16 @@ This includes:
 
 ## What Is Internal
 
-Modules under `libtmux._internal` and `libtmux._vendor` are **not public**.
-They may change or be removed without notice between any release.
+Modules under `libtmux._internal`, `libtmux._vendor`, and
+`libtmux._experimental` are **not public**. They may change or be removed
+without notice between any release. `libtmux._experimental` additionally hosts
+in-progress designs that are published for feedback before any stability
+commitment (see {ref}`the experimental docs <experimental>`).
 
 Do not import from:
 - `libtmux._internal.*`
 - `libtmux._vendor.*`
+- `libtmux._experimental.*`
 
 ## Pre-1.0 Stability Policy
 

pyproject.toml

@@ -65,6 +65,7 @@ dev = [
   "pytest-mock",
   "pytest-watcher",
   "pytest-xdist",
+  "pytest-asyncio",
   # Coverage
   "codecov",
   "coverage",
@@ -87,6 +88,7 @@ testing = [
   "pytest-rerunfailures",
   "pytest-mock",
   "pytest-watcher",
+  "pytest-asyncio",
 ]
 coverage =[
   "codecov",
@@ -242,6 +244,8 @@ doctest_optionflags = [
   "ELLIPSIS",
   "NORMALIZE_WHITESPACE"
 ]
+asyncio_mode = "strict"
+asyncio_default_fixture_loop_scope = "function"
 testpaths = [
   "src/libtmux",
   "tests",

src/libtmux/_experimental/__init__.py

@@ -0,0 +1,13 @@
+"""Experimental libtmux APIs.
+
+Note
+----
+This is an **experimental** namespace. Everything under
+:mod:`libtmux._experimental` is **not** covered by the project's versioning
+policy and may change or be removed between any releases without notice.
+
+If you depend on something here and want it stabilized, please
+`file an issue <https://github.com/tmux-python/libtmux/issues>`_.
+"""
+
+from __future__ import annotations