Observability

[SETTLED] Events flow through a sink trait parameter. A no-op sink inlines to nothing — observability is free when off, always available when wanted. Unconditional emission on hot paths is banned.

[DESIGN] The demand-event vocabulary preserves the current driver's distinctions: demanded, the three memo-hit tiers with verified counts, spawned (fn-level and exact-invocation-level separately), parked, completed, store-alloc with dedup bit, the exec lifecycle triple carrying the tier verdict, generic observations with replay bit, and artifact-probe events with their own cache bit. Four reuse axes, four event shapes (machine.arch.reuse-axes-distinct).

[DESIGN] Standing counters: hostcalls per inner-loop iteration, scheduler requests per iteration, interns per branch, memo hit economics (hits, verified-counts, allocation on hit = 0), effect-pool saturation. Counters are load-independent attribution — the instrument of record when wall clocks lie.

[DESIGN] Stax sees everything: jitdump/DWARF registration wired for every compiled stencil (the mechanism exists in weavy; WIRING it is the rule), phase spans at machine boundaries (demand entry, freeze, effect begin/ complete) as user events. A profile with anonymous regions is a spec violation, not a tooling gap.

[SETTLED] Graph VIR, partitioned VIR, lowered Weavy IR, native mapping tables, and the source-map chain have deterministic text plus typed inspection forms. A machine whose compiled form cannot be read is unreviewable by construction.

[SETTLED] Observability surfaces do not clone the world: a debug/inspection snapshot is a view, iterator, or copy-on-write, never an O(store) allocation. (L11's observability half; the store half is machine.store.snapshot-no-clone.)

[SETTLED] Every conservative fallback — safe-miss, safe-rebuild, safe-false — emits a reasoned event. A receipts system cannot contain a rebuild cause that leaves no receipt; "correct but slow" gets the same rigor as "wrong" because nothing else ever catches it.

[DESIGN] Nondeterminism is machine-detected: diverging read-sets or results on a memo re-run (machine.memo.rerun-audit) surface as typed events. Flakiness is an observation, not folklore.