Q-W5: persist → session/ext_state_io/prune_fs (deletion authority concentrated); one GetProjExtState grow-loop in bridge_marshal (T2-04, ×3 rewired); bank_book JSON codec → bank_book_json via private static nameKey; persist.h stays umbrella. 61/61 green.

src/shell/instrument/reaper_bridge.cpp

@@ -93,21 +93,19 @@ std::optional<std::string> ReaperBridge::readReasamplerExtState(const std::strin
 
     // GetProjExtState writes into a caller buffer; the bank blob can be large (many
     // samples), so grow the buffer until the value fits rather than risk a silent
-    // truncation — mirrors persist.cpp's getProjExtStateString growing strategy. The
-    // return value is the value length; if it fits strictly inside the buffer it is
-    // complete, else grow and retry up to a 16 MB ceiling.
-    for (int cap = 1 << 16; cap <= (1 << 24); cap <<= 2) {
-        std::vector<char> buf(static_cast<std::size_t>(cap), '\0');
-        const int rv = getProjExtState_(proj, kProjExtNamespace(), key.c_str(),
-                                        buf.data(), cap);
-        if (rv <= 0) return std::nullopt;  // absent / empty key
-        std::string s(buf.data());
-        if (static_cast<int>(s.size()) + 1 < cap) {
-            return decodeGetProjExtState(rv, s);
-        }
-        // else: possibly truncated -> grow and retry.
-    }
-    return std::nullopt;  // pathologically large (>16 MB) — give up rather than loop
+    // truncation. The retry policy is the SHARED pure
+    // instrument::map::readProjExtStateGrowing (Q-W5 rider T2-04 — one loop for the
+    // extension's persist/usage reads and this bridge read; the rules cannot drift):
+    // absent (rv <= 0) and the >16 MB ceiling both fold to nullopt here, and a
+    // complete value still runs through decodeGetProjExtState (the stale/empty-buffer
+    // guard) exactly as before.
+    const auto read = instrument::map::readProjExtStateGrowing(
+        [&](char* buf, int cap) {
+            return getProjExtState_(proj, kProjExtNamespace(), key.c_str(), buf, cap);
+        });
+    if (read.status != instrument::map::GrowingExtStateRead::Status::Complete)
+        return std::nullopt;  // absent / empty key, or pathologically large (>16 MB)
+    return decodeGetProjExtState(read.apiReturn, read.value);
 }
 
 bool ReaperBridge::writeUsageExtState(const std::string& usageKey,