feat(soul): write-through to the persistence owner — memories survive restart (#117)

The soul obeys half of its own ownership rule. soul.el:571-573 says "when
ENGRAM_URL is set the HTTP Engram owns persistence — the soul must NEVER write
to the local snapshot", and it doesn't. But nothing was ever built to hand the
soul's writes TO that owner: sync is pull-only (/api/sync -> engram_load_merge),
so every node created inside the soul lived in process RAM and was shed on
restart. Measured live 2026-08-07: soul node_count=102184, engram 79197.

SCOPE CORRECTION vs the earlier internal spec: engram provisional claim 17's
"pull-then-push" is a PEER-ENGRAM to PEER-ENGRAM protocol (claims 15-18 say so
explicitly). The soul is a CALLER of the database API, not a peer. Claim 17 is
NOT authority for a soul<->engram contract and is no longer cited as such. The
design here follows from the ownership rule alone.

Mechanism: a new Accessor, persist.el, is the single boundary. Writes stage a
delta to a filesystem spool and are pushed to the owner via POST /api/load-merge
— NOT POST /api/nodes, which mints a new server-side id (breaking dedup and
edges) and drops label/tier/tags/importance/confidence (verified in a sandbox:
a tier "Canonical" probe came back "Working"). load-merge preserves the id and
every field, dedups nodes by id and edges by (from,to,relation) so retries are
no-ops, and calls persist_canonical() so THE OWNER writes its own file — the
ownership rule is honoured rather than worked around.

Spool-and-drain rather than push-per-write: measured ~0.38s per load-merge at
live scale (79k nodes/176MB), and a chat turn writes 5-7 nodes. The spool is on
disk, not in process state, because the soul serves each connection on its own
pthread and a shared buffer would lose entries to a read-modify-write race. That
also buys crash recovery: writes orphaned by kill -9 are drained on next boot.

Honesty: api_persisted (the gate all 10 MCP write handlers pass through) and
mem_store now assert AT THE OWNER instead of reading back the soul's own RAM.
With the owner down a write returns {"ok":false,"error":"write_not_persisted"}
and the delta is queued — where main returns {"ok":true} for a write that dies.

Coverage: 35 node sites + 9 edge sites routed through the boundary. Deliberately
excluded, with reasons in persist.el: 4 InternalStateEvent sites (Will's own
telemetry carve-out), the boot counter and the persona (both already have
bespoke owner-side write-backs), and soul.el's 54 genesis identity edges
(file-mode only). engram_strengthen and engram_forget are NOT propagated —
load-merge cannot update or delete, and hard-deleting at the owner would fail
verify-soul-contract.sh section B.

Also fixed here:
- routes.el GET /api/graph/edges engram_save()'d straight over the owner's
  canonical snapshot.json — a read route, in a non-owner process, clobbering the
  canonical on every call. Same defect class Will removed from the engram in el
  dc39a61. Now exports to a scratch path. With this gone the soul writes nothing
  at all in HTTP mode.
- persist.el must clear the runtime's _tl_fs_read_len hint after every fs_read.
  In vendored runtime v1.0.0-20260501 that hint becomes the NEXT response's
  Content-Length, so reading a spool file mid-request made an 86-byte reply go
  out as 497 bytes with 411 bytes of adjacent heap trailing it. Caught and fixed
  at our boundary; the runtime class was fixed upstream in el 43636ae, which is
  not the pinned runtime here.

Rung: E2E-VERIFIED, discriminating. Same harness, same engram binary:
  write-through: LEG 1 PRESENT at owner, LEG 2 SURVIVED kill -9 + restart
  main:          LEG 1 ABSENT  at owner, LEG 2 LOST
verify-soul-contract.sh: GATE PASS on both builds (27/27 routes, immutability).

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

chat.el

@@ -1162,7 +1162,7 @@ fn hist_trim_with_bell_guard(hist: String) -> String {
             + " | evicted_at:" + ts_str
             + " | message:" + safe_content
         let preserve_tags: String = "[\"bell-history\",\"bell:" + bell_level + "\",\"evicted\",\"affective\",\"BellEvent\"]"
-        let discard: String = engram_node_full(
+        let discard: String = wt_node(
             preserve_content,
             "BellEvent",
             "bell:" + bell_level + ":preserved",
@@ -1210,7 +1210,7 @@ fn conv_history_persist(session_id: String, hist: String) -> Void {
     if !str_contains(hist, "]") { return "" }
     let tags: String = "[\"conv-history\",\"persistent\"]"
     // FIX B: one label rule, shared with the agentic path. See conv_hist_label.
-    let node_id: String = engram_node_full(
+    let node_id: String = wt_node(
         hist, "Conversation", conv_hist_label(session_id),
         el_from_float(0.7), el_from_float(0.8), el_from_float(0.9),
         "Episodic", tags
@@ -3461,7 +3461,7 @@ fn handle_dharma_room_turn(body: String) -> String {
     // engram_node(content, "episodic", ...) which wrongly put a TIER into the node_type
     // slot — that's why nodes showed node_type="episodic". Use the full, correct contract.)
     let utterance_tags: String = "[\"soul-utterance\",\"episodic\"]"
-    let discard_id: String = engram_node_full(
+    let discard_id: String = wt_node(
         clean_response, "Conversation", "soul:utterance",
         el_from_float(0.6), el_from_float(0.6), el_from_float(0.8),
         "Episodic", utterance_tags
@@ -3552,7 +3552,7 @@ fn session_summary_write(summary_text: String) -> String {
         }
     }
     let tags: String = "[\"SessionSummary\",\"session-summary\",\"previous-session\",\"consolidate\"]"
-    let node_id: String = engram_node_full(
+    let node_id: String = wt_node(
         content, "SessionSummary", "session:summary",
         el_from_float(0.85), el_from_float(0.85), el_from_float(1.0),
         "Episodic", tags
@@ -3578,7 +3578,7 @@ fn session_summary_write_dated(summary_text: String, label: String) -> String {
     let ts_str: String = int_to_str(ts)
     let content: String = "[session-summary] " + trimmed + " | ts:" + ts_str
     let tags: String = "[\"SessionSummary\",\"session-summary\",\"previous-session\",\"consolidate\"]"
-    let node_id: String = engram_node_full(
+    let node_id: String = wt_node(
         content, "SessionSummary", label,
         el_from_float(0.9), el_from_float(0.8), el_from_float(1.0),
         "Episodic", tags
@@ -3654,7 +3654,7 @@ fn auto_persist(req: String, resp: String) -> Void {
         + ",\"bell\":\"" + bell_level + "\""
         + ",\"label\":\"chat:" + ts_str + "\"}"
 
-    let conv_node_id: String = engram_node_full(
+    let conv_node_id: String = wt_node(
         content,
         "Conversation",
         "chat:" + ts_str,
@@ -3692,7 +3692,7 @@ fn auto_persist(req: String, resp: String) -> Void {
         let bell_tags: String = "[\"safety\",\"bell\",\"bell:" + bell_level + "\",\"affective\",\"BellEvent\"]"
         let bell_ts_str: String = int_to_str(time_now())
         let bell_label: String = "bell:" + bell_level + ":" + bell_ts_str
-        let bell_node_id: String = engram_node_full(
+        let bell_node_id: String = wt_node(
             bell_content,
             "BellEvent",
             bell_label,
@@ -3751,7 +3751,7 @@ fn auto_persist(req: String, resp: String) -> Void {
         let pos_tags: String = "[\"joy\",\"positive\",\"joy:" + positive_level + "\",\"affective\",\"PositiveEvent\"]"
         let pos_ts_label: String = int_to_str(time_now())
         let pos_label: String = "joy:" + positive_level + ":" + pos_ts_label
-        let pos_node_id: String = engram_node_full(
+        let pos_node_id: String = wt_node(
             pos_content, "PositiveEvent", pos_label,
             pos_sal_a, pos_sal_b, pos_sal_c, "Episodic", pos_tags
         )