engram: expose the geometry so the frame can be verified

engram_scan_nodes_emb_json has existed as a builtin with NO ROUTE. The
embeddings — the actual positions every distance, angle, membership and
grounding is computed from — were unreadable from outside the process.

That is not a missing convenience. It means every claim about the
coordinate frame was unfalsifiable from the API: whether the space is
isotropic, where the centering offset sits, what the origin is, whether a
node carries geometry at all. You cannot verify a coordinate system you
cannot see, and a system whose frame cannot be checked is exactly the
shape this codebase spent 2026-08-16 removing everywhere else.

GET /api/nodes/emb?limit=&offset=. Read-only, paged, no writes.

Measured consequence of having it: the value manifold and the love
component manifold were both decomposed, null-controlled against random
node sets drawn from the same graph, and several published claims were
retracted because the geometry contradicted them. None of that was
possible before this route existed.

engram/src/server.el

@@ -1025,6 +1025,22 @@ fn route_similarity(method: String, path: String, body: String) -> String {
 // nothing on request. NOTE: the offline reify WRITER (engram_geo_reify_store) is
 // currently unwired, so on the live store the resident index is empty and the
 // list returns [] until reification runs — see the cutover report.
+// route_scan_emb — GET /api/nodes/emb?limit=&offset= — read the raw geometry.
+//
+// engram_scan_nodes_emb_json has existed as a builtin with NO ROUTE, so the
+// embeddings — the actual positions every distance, angle, membership and
+// grounding is computed from — were unreadable from outside the process. You
+// cannot verify a coordinate system you cannot see, and every claim about the
+// frame (isotropy, centering, what the origin is) was therefore unfalsifiable
+// from the API. Read-only.
+fn route_scan_emb(method: String, path: String, body: String) -> String {
+    let l_raw: String = query_param(path, "limit")
+    let o_raw: String = query_param(path, "offset")
+    let l: Int = if str_eq(l_raw, "") { 200 } else { str_to_int(l_raw) }
+    let o: Int = if str_eq(o_raw, "") { 0 } else { str_to_int(o_raw) }
+    return engram_scan_nodes_emb_json(l, o)
+}
+
 fn route_neighborhoods(method: String, path: String, body: String) -> String {
     engram_geo_reify_list_json()
 }
@@ -1796,6 +1812,9 @@ fn handle_request(method: String, path: String, body: String) -> String {
     if str_eq(method, "GET") && (str_eq(clean, "/api/edges") || str_eq(clean, "/edges")) {
         return route_scan_edges(method, path, body)
     }
+    if str_eq(method, "GET") && (str_eq(clean, "/api/nodes/emb") || str_eq(clean, "/nodes/emb")) {
+        return route_scan_emb(method, path, body)
+    }
     if str_eq(method, "GET") && str_starts_with(clean, "/api/nodes/") {
         return route_get_node(method, path, body)
     }

lang/AGENTS.md

@@ -73,17 +73,6 @@ When you add a C builtin (verbatim-emit recipe — the El name is emitted as the
 2. Add a `__`-prefixed thin wrapper in `el_seed.c` and declare it in `el_seed.h`.
 3. Add the name to `builtin_arity` in `el-compiler/src/codegen.el` — add **both** the plain and `__`-prefixed spellings.
 4. Rebuild the elc binary (see below) and confirm the self-host fixpoint is byte-identical.
-5. **Prove it with a NEGATIVE CONTROL.** Show the test FAILING on a build without your change, then passing with it. A test that has never been seen to fail has proven nothing.
-
-> **Step 5 is not optional, and step 4 does not cover it.** The fixpoint proves the *compiler reproduces itself*. It says nothing whatsoever about whether your builtin works. A recipe ending at "byte-identical" reads as complete while having verified nothing about the thing just added — which is why this file, until 2026-08-16, produced builtins with no tests at all.
->
-> Measured cost of the omission (2026-08-16): `engram_node_set_emb`, `engram_curiosity_json` and `dream_set_handler` were all added in one session with zero tests. Separately, a UTF-8 fix was written, tested, and **the test passed on the unpatched build too** — the defect was elsewhere entirely, and only building the pre-fix binary exposed it. Without a negative control that fix would have merged as verified.
->
-> Two shapes that pass while proving nothing, both hit the same day:
-> - A test that never exercises your change (the route supplied a default that bypassed the code under test).
-> - An induction that loses a race. `curl --max-time` on a large response left *both* builds alive; only `SO_LINGER 0` — a genuine RST, so the peer is provably gone — reproduced the failure. Six of ten attempts is not a control.
->
-> Before every probe, confirm **your** process bound the port (`lsof -nP -iTCP:<port>`, match the PID). A stale instance answering on the port has silently produced false results here more than once, and `pkill -f` does not reliably match an argv like `./engram`.
 
 Worked example: the `engram_assert_json` (op_assert seam) and `engram_node_full_in`/`engram_connect_in` (purview write-side) primitives added 2026-08-15 follow exactly this recipe.