Pinned Wasmtime reentrancy fixture crosses a synchronous instance boundary

[lannbot]

Finding

Pinned Wasmtime cc546eee265b805dda0f034b2007d110a541093d adds
tests/misc_testsuite/component-model/thread-transparency/reentrancy.wast.
Its line 114 expects the outer thread to reenter Mid and reach a guest
unreachable. Component Model reference a53b241d4d50487d256900fcad77cd6cda51808f
requires an earlier synchronous-block trap.

Evidence

• Outer.run is async-typed and callback-lifted. It creates a second ready Outer
  thread with thread.resume-later, then calls Mid.f.
• Mid.f is synchronous-typed and synchronously lifted. It calls Inner.g.
• Inner.g is async-typed but synchronously lifted. It waits on a fresh empty
  waitable set, with no producer.
• Inner's async canon_lift returns blocked. Mid's sync canon_lower waits for
  the result. Mid's synchronous canon_lift must drive only ready threads in
  Mid's own instance and trap when that candidate set is empty.
• Mid has no eligible thread. Outer's ready thread is in another instance.

Authorities in pinned definitions.py: canon_lift (sync instance-local loop),
canon_lower (sync wait for resolution), Thread.resume (explicit direct
transfers), and Store.tick (top-level nesting requirement). No direct transfer
occurs in this fixture; resume-later only makes a thread ready.

Polyengine trace confirms an empty Mid candidate set and a ready Outer thread.
The result is wasm trap: cannot block a synchronous task before returning,
not the fixture's wasm unreachable instruction executed category. This is
independent of FIFO/seed choice because Mid has zero candidates.

Handling

Keep the supplementary assertion executed and classify the exact mismatch
separately from runtime defects. Do not equate the two trap conditions, exclude
the file, or widen the synchronous candidate set. Revisit after upstream
adjudication or a future spec/test revision.

This finding is based on pinned source and a polyengine trace, not a newly
measured native Wasmtime run. No upstream issue/comment has been filed.

Related inventory: #372.