Add 2D grid program_id semantics (ADR-0022)

tl.program_id(axis=0) returns local PE id within cube,
tl.program_id(axis=1) returns cube id. Enables cube-aware
sharding in benchmark kernels.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/kernbench/triton_emu/tl_context.py

@@ -53,9 +53,13 @@ class TLContext:
         num_programs: int = 1,
         dispatch_cycles: int = 1,
         runner: Any = None,
+        cube_id: int = 0,
+        num_cubes: int = 1,
     ) -> None:
         self._pe_id = pe_id
         self._num_programs = num_programs
+        self._cube_id = cube_id
+        self._num_cubes = num_cubes
         self._dispatch_cycles = dispatch_cycles
         self._commands: list[PeCommand] = []
         self._handle_counter = 0
@@ -234,11 +238,23 @@ class TLContext:
     # ── Index / Scalar (PE_CPU, no engine) ────────────────────────
 
     def program_id(self, axis: int = 0) -> int:
-        """Return program instance index."""
+        """Return program instance index.
+
+        axis=0: local PE id within cube.
+        axis=1: cube id.
+        """
+        if axis == 1:
+            return self._cube_id
         return self._pe_id
 
     def num_programs(self, axis: int = 0) -> int:
-        """Return total number of program instances."""
+        """Return total number of program instances.
+
+        axis=0: num PEs per cube.
+        axis=1: num cubes.
+        """
+        if axis == 1:
+            return self._num_cubes
         return self._num_programs
 
     def arange(self, start: int, end: int, dtype: str = "i32") -> TensorHandle: