prevent engram corruption: idempotent boot seeding, session-start event cap

Fix 1: mem_boot_count_inc prunes all existing soul:boot_count nodes before
        inserting the new one — keeps exactly one boot counter node instead
        of accumulating a new node per boot. Also fixes a latent ordering
        bug where engram_search_json oldest-first results caused the counter
        to read stale (low) values once >3 copies accumulated.

Fix 3: handle_api_node_delete comment clarified — the no-verify exception
        is correct for deletes (not a write path); read-back-verify is for
        writes only.

Fix 4: emit_session_start_event prunes old session-start InternalStateEvent
        nodes after each boot, keeping the 10 most recent and forgetting
        older ones. Prevents unbounded accumulation of ~120+ copies.

memory.el

@@ -134,12 +134,30 @@ fn mem_boot_count_get() -> Int {
     return str_to_int(num_str)
 }
 
-// mem_boot_count_inc — increment boot counter, store new node, return new count.
-// Each boot creates a new "soul:boot_count:N" node. Old ones accumulate as
-// history — the search above always returns the highest value seen.
+// mem_boot_count_inc — increment boot counter, store a single canonical node, return new count.
+// Prunes ALL existing soul:boot_count nodes before inserting the new one so there is
+// always at most ONE such node in the graph. Without pruning, engram_node_full inserts
+// a new node every boot (no upsert) and the old ones accumulate. The search-first
+// approach also fixes a latent ordering bug: engram_search_json returns oldest-first,
+// so mem_boot_count_get() with limit=3 would read a stale (lower) count once more
+// than 3 copies accumulate.
 fn mem_boot_count_inc() -> Int {
     let current: Int = mem_boot_count_get()
     let next: Int = current + 1
+    // Prune all existing boot_count nodes — keep exactly one.
+    let old_results: String = engram_search_json("soul:boot_count", 50)
+    if !str_eq(old_results, "") && !str_eq(old_results, "[]") {
+        let old_len: Int = json_array_len(old_results)
+        let oi: Int = 0
+        while oi < old_len {
+            let old_node: String = json_array_get(old_results, oi)
+            let old_id: String = json_get(old_node, "id")
+            if !str_eq(old_id, "") {
+                engram_forget(old_id)
+            }
+            let oi = oi + 1
+        }
+    }
     let content: String = "soul:boot_count:" + int_to_str(next)
     let tags: String = "[\"soul-meta\",\"boot-counter\"]"
     let boot_node_id: String = engram_node_full(