Why

The catalog already assigns stable ${packId}:${localId} level IDs, but the application still carries the active proof as a mutable array index while catalog access repeatedly clones every pack and level. Pack replacement, removal, progress updates, and win handoff can therefore resolve different levels after the catalog changes, while ordinary UI refreshes pay a full catalog clone cost.

What Changes

• Make the canonical active-level identity the existing stable global level ID, while retaining numeric index arguments for compatibility.
• Define catalog read boundaries that resolve one level or the active level by stable ID and invalidate derived views after register, replace, and remove.
• Keep existing public clone and mutation-safety guarantees for getLevels, getLevel, and getPack; add focused cache and identity tests before changing callers.
• Migrate application handoff, progress marking, level replacement, and pack removal flows to re-resolve by stable ID instead of retaining a stale index.

This change does not alter pack IDs, local level IDs, sharing payloads, save keys, solver state, or level ordering semantics.

Capabilities

New Capabilities

• stable-active-level-identity

Modified Capabilities

None.

Impact

src/catalog.js, src/main.js, and their focused tests will change. Existing catalog methods remain compatible and continue returning caller-owned data. The implementation may add internal generation counters or immutable records, but those details are not exposed in pack or level payloads.