[ariscript]

First of three stacked follow-ups to #573, in the order agreed on that PR: gate layout (this PR),
then rounds (#617), then destinations and arrival groups (#618). They address @dsidler's review points
1 and 4.

What changes

• Gates are one int32 symmetric tensor: a counter and an arrival counter per chunk, then a completion
  counter per peer.
• The copy engine polls a chunk's counter against writers × round, so mark_ready is a single
  release atomic. There is no last-writer election and no separate ready word.
• plan.counters is contiguous int32, so a kernel that signals per tile can increment it directly
  instead of calling TriggeredView.mark_ready. That includes a tritonBLAS EpilogueConfig(counter_buffer=...)
  (Add SignalView and WaitView tritonBLAS#81).
• Every round, each peer queue's chains end with one copy-engine add on the sending rank's completion
  counter for that peer:
  • plan.wait() now reads only local memory; the progress kernel's remote reads are gone.
  • Kernels can wait inline with the new TriggeredView.sent() / wait_sent(), for example before
    overwriting their source.
• Limit: writers × round must stay at or below 2³¹ − 1 (over 7M rounds at 304 writers).

Testing (MI300X, torch allocator)

• tests/unittests/test_plan.py at 2 and 4 ranks. New tests:
  • a kernel that increments plan.counters with a plain gpu-scope atomic_add after
    debug_barrier, as the tritonBLAS epilogue does: 8 writers on one 4 MiB chunk, 10 rounds,
    no stale data;
  • wait_sent before reusing the source;
  • the round limit.
• View tests (Triton and Gluon) on one GPU.
• Docs build.

[Copilot]

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Copilot review overview

4 open issues

• Same issue as the Triton path: the loop bound is loaded at runtime, but the Python range(...) in… · New
• In Triton, range(...) must have a compile-time constant bound; `tl.load(self.view +… · New
• tl.constexpr is meant to be used as a parameter annotation in Triton kernel signatures, not… · New
• H_SENDS_TO is stored in a single int64 header word (bitmask), which cannot represent `world_size… · New

What changed in this PR

Updates triggered-plan gate layout and device/host synchronization to use contiguous int32 counters (per-chunk marks + arrivals, and per-peer completion), enabling single-atomic mark_ready and local-only wait() progress checks.

Changes:

• Replace per-chunk “ready word + counter” gate rows with int32 counters/arrivals and per-peer completion counters (ABI v2).
• Add device APIs TriggeredView.sent() / wait_sent() and host-side completion signaling per peer queue.
• Update unit tests and docs to reflect the new gate tensor layout and semantics.

File	Description
iris/​experimental/​plan/​triton.py	Switches device ABI/layout to int32 gates and adds sent()/wait_sent() logic.
iris/​experimental/​plan/​gluon.py	Mirrors Triton TriggeredView changes for Gluon device code.
iris/​experimental/​plan/​triggered.py	Allocates/slices new gate tensor, adds round limit check, and switches wait logic to local-only gates.
iris/​experimental/​plan/​kernels.py	Replaces progress kernel with local-only wait kernel; updates release semantics.
iris/​experimental/​plan/​armer.py	Arms chains polling counter thresholds and signals int32 arrivals + per-peer completion.
tests/​unittests/​test_plan.py	Adds coverage for external counter increments, wait_sent, and round limit; updates arrivals assertions.
tests/​unittests/​test_plan_view.py	Updates view tests for new counter/arrival layout and adds sent()/wait_sent() coverage.
tests/​unittests/​test_plan_view_gluon.py	Updates Gluon view tests similarly and adds sent()/wait_sent() coverage.
docs/​conceptual/​triggered-plans.md	Updates conceptual model and memory-ordering text for counter-based gating and completion counters.
docs/​reference/​host/​plan.md	Exposes new device methods sent/wait_sent in API docs.
iris/​experimental/​plan/​__init__.py	Updates module docstring to mention new device APIs.

_{Review effort: Lite}