Fix actor/task flow fixed-point convergence

[BoSuY0]

Summary

Fixes the inherited actor/task semantic flow fixed-point blocker:

TestActorTaskBoundedStressExamples/task_bounded_stress
examples/tasks/task_bounded_stress.tetra:14:5:
flow fixed point did not converge

This is semantic flow fixed-point convergence cleanup, not actor feature work.

Root cause

The loop-local task handle in task_bounded_stress.tetra was assigned a fresh resource id on each loop fixed-point iteration. core.task_join_i32(task) marked that id as finalized, then scope cleanup removed the scoped resourceVars["task"] path but left the id-keyed finalizedResources[id] fact behind. The fixed-point state therefore grew by one orphan finalization id per iteration and never converged within the existing limit.

The fix prunes id-keyed resource flow facts when a scoped local resource path is removed and no remaining resource path references that id.

Scope / nonclaims

• fixes inherited actor/task flow fixed-point blocker;
• no Actor Core v2;
• no distributed actors;
• no actor runtime behavior change;
• no Memory Core change;
• no optimizer change;
• no .t4i or .tobj change;
• no release approval;
• no security signoff.

Validation

Focused:

go test -buildvcs=false \
  ./compiler/tests/ownership/actor_task/... \
  -run 'TestActorTaskBoundedStressExamples|FlowFixedPointActorTask' \
  -count=20 \
  -v

Result: pass.

go test -buildvcs=false \
  ./compiler/internal/semantics/flow \
  -run 'FixedPoint|Join|Digest|Actor|Task|Await|Callable' \
  -count=20

Result: pass.

go test -buildvcs=false \
  ./compiler/internal/semantics/... \
  -run 'FixedPoint|Actor|Task|Transfer|Await|Callable' \
  -count=10

Result: pass.

Guards:

go test -buildvcs=false \
  ./compiler/internal/actorsafety/... \
  ./compiler/internal/actorsrt/... \
  ./compiler/internal/parallelrt/... \
  ./compiler/actorwire/... \
  ./cli/internal/actornet/... \
  -count=5

Result: pass.

go test -buildvcs=false \
  ./compiler/internal/t4iface \
  ./compiler/internal/format/tobj \
  ./compiler/internal/buildlink/... \
  -count=3

Result: pass.

go run ./tools/cmd/verify-docs --manifest docs/generated/manifest.json

Result: pass.

Broad delta:

• go test -buildvcs=false ./compiler/... -count=1: red from inherited baseline failures only; compiler/tests/ownership/actor_task is now green.
• go test -buildvcs=false ./cli/... ./tools/... -count=1: red from workspace wrapper around the same inherited compiler failures.

Inherited remaining classes include ownership diagnostic mismatch, selective-import actor payload diagnostics, secret/capsule effects diagnostics, and surface frame diagnostic wording.