Make completed MultiCompiler cohorts authoritative without FIFO hook identity

[ScriptedAlchemy]

Follow-up to the Rsbuild conformance audit: #72.

Problem

The runtime compile observer assigns an attempt ID in global onBeforeDevCompile and consumes IDs FIFO in onAfterDevCompile. Rsbuild documents lifecycle order but not a stable cycle ID, exact callback cardinality under coalesced invalidations, or one-to-one pairing when MultiCompiler children invalidate at different times. Rsbuild 2.2.1's shared-promise invalidation deduplication and synthesized global completion are implementation details.

A minor scheduling change can associate MultiStats with an older attempt, leave a newer activation barrier unsettled, or wedge generation supersession. The bounded conformance fix detects any non-singleton pending queue, fails all live attempts, and throws rather than silently misassociating them.

Proposed direction

• Treat each successful completed MultiStats cohort as the authoritative monotonic identity.
• Keep pre-compile observation advisory; it must not own an activation-blocking barrier.
• Base supersession on completed cohort ordinals and prepared-runtime authority.
• Add deterministic tests for coalesced, missing, duplicated, and reordered global callbacks plus skewed child invalidations.

Acceptance

• No generation identity depends on FIFO position between global hooks.
• Missing/duplicate/reordered callbacks cannot wedge activation or associate Stats with stale state.
• Existing failed/no-op attempt and commit-window protections remain intact.

[ScriptedAlchemy]

Issue audit result: this is not superseded by the #93-#105 meta-framework stack. It is the remaining low-level dev-runtime correctness follow-up from #72. Implementation remains in PR #83; keep this issue open until that PR lands.