- tensor_get now parses indices from string symbols (not binary u32),
  matching how MeTTa S-expressions encode numbers
- End-to-end test exercises full pipeline: load data → tensor_collect →
  tensor_einsum → tensor_get to verify C[0,0]=19.0 and C[1,1]=50.0
- TensorEinsumSink strips quotes from spec string
- Command sinks (einsum, binop, free) parse args in new() for literal
  templates, or in sink() for variable-bound templates

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

The opaque context pointer now flows through the extern "C" call
signature rather than being set on each ExprSource before dispatch.
tensor_get/tensor_nnz read it directly from the arg; EvalScope.context
and ASink::set_context remain the owner-facing knob.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

The `parsed` guard in `sink()` captured only the first pattern match and
dropped subsequent ones, so `(exec (, (to_free $n)) (O (tensor_free $n)))`
freed one tensor regardless of how many facts matched. Collect all names
across `sink()` calls and drain them in `finalize()`. The test exercises
three concurrent matches with one non-match that must survive.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Both pass — the basic TensorBinopSink path works for constant names
under an empty `(,)` pattern. Does not yet cover variable-bound names
or multi-match dispatch, which are the likelier breakage surfaces
hinted at by the todo comment.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Drop the `entries: Vec<(Vec<usize>, f64)>` buffer — parse each matched
tuple in `sink()` and call `SparseTensorF64::set` on the stored tensor
directly. The first match replaces any existing tensor at `name` with a
fresh one of the sink's rank, so repeated exec invocations start clean;
subsequent matches in the same invocation accumulate. Tracked with one
`initialized: bool` instead of the entry Vec. Safe as long as no
concurrent tensor-as-source path reads `name` during the exec.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>