engram: ranked BM25+recency search replaces storage-order substring; URL-decode GET query params

Measured on the live container mind (pinned 40-query eval, judged): substring
2/40=5% hit@5 -> ranked 35/40=88%. Multi-word queries stop returning zero; new
memories stop losing to storage order (created_at tiebreak). Transparent-layer
identity filter preserved in both passes; jb_finish (#64) tail preserved.
query_param now url_decode()s values - %XX arrived literal before (pre-existing
GET defect, masked while multi-word substring returned nothing anyway).
E2E-verified in Tim's container deployment 2026-07-14/15; eval harness:
docs repo research-archive/p0-prototypes/eval_pinned_40q_20260715.py.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

engram/src/server.el

@@ -50,8 +50,12 @@ fn query_param(path: String, key: String) -> String {
     if pos < 0 { return "" }
     let after: String = str_slice(qs, pos + str_len(needle), str_len(qs))
     let amp: Int = str_index_of(after, "&")
-    if amp < 0 { return after }
-    str_slice(after, 0, amp)
+    // SPEC-SEARCH-UPGRADE 2026-07-14: URL-decode the extracted value (%XX and
+    // '+' were previously passed through literally, so an encoded multi-word
+    // query arrived as junk tokens — pre-existing GET-path defect, masked
+    // until search could actually rank multi-word queries).
+    if amp < 0 { return url_decode(after) }
+    url_decode(str_slice(after, 0, amp))
 }
 
 fn query_int(path: String, key: String, default_val: Int) -> Int {