pS-usage: captures held by live ReaSampler 9000 instances are un-prunable — instances publish usage_<guid> ext-state records (ComponentState v11), prune unions live holds into referenced

src/ext_keys.h

@@ -69,4 +69,23 @@ inline constexpr const char* kProjExtBankGenKey = "bank_generation";
 // changing this spelling strands any pending request an already-shipped instrument watches.
 inline constexpr const char* kProjExtAssignKey = "assign_request";
 
+// The pS-usage PER-INSTANCE USAGE-RECORD key prefix. The INSTRUMENT writes one key per
+// instance — "usage_<instanceGuid>" — carrying the sample_usage wire record of every
+// capture that instance holds; the EXTENSION enumerates the prefix at prune-scan time
+// and folds live instances' holds into the prune's `referenced` set so a held capture
+// can never be pruned. This is the ONE sanctioned instrument-side ext-state write
+// (Daniel's ruling — the VST publishes its OWN usage; it never mutates banks/view/
+// tail/assign, and the bridge's write entry point structurally accepts only this
+// prefix). WIRE-SHARED in the write->read direction the other keys reverse. FOREVER-
+// STABLE once shipped: changing the prefix strands every saved project's usage records
+// (prune falls back to bank-references-only until instances republish — graceful, but
+// the instance-hold protection lapses for stale-saved projects).
+inline constexpr const char* kProjExtUsageKeyPrefix = "usage_";
+
+// The full per-instance usage key for a minted instance GUID (the one composition
+// point, shared by the instrument's writer and the extension's enumerator).
+inline std::string usageKeyFor(const std::string& instanceGuid) {
+    return std::string(kProjExtUsageKeyPrefix) + instanceGuid;
+}
+
 }  // namespace reasampler