swarm: Rule 4 — engram-write is @manager-ONLY, enforced by capability

New hard invariant (Will): only the orchestrator mutates global engram state;
workers are read-only against the full engram + write only their own local
geometry. This is an AUTHORITY gate (capability), not a health gate — a worker
is STRUCTURALLY UNABLE to mutate global engram state regardless of engram health.

- containment.el: scope tokens now carry a caps set. Orchestrator token holds
  engram:write + dharma:emit (@manager-only, the VBD rule that only the manager
  mutates global state); worker token holds ONLY engram:read. Rule 4:
  containment_check_engram_write / _dharma_emit reject any caller lacking the
  capability — same scope-token mechanism as the live Rule-2 denial.
- swarm.el: swarm_engram_write is the ONLY engram write path, gated by Rule 4;
  a worker token is denied before any HTTP is issued (no mutation). The curated
  merge (commit=1) is the sole writer: the orchestrator commits approved
  geometry via its write-capable token. Workers' full-engram READ stays intact.
- reshape_surface.el: compose op_write (json_escape_string) for the commit path.
- harness: Rule-4 suite proven — worker engram-write DENIED by capability, no
  node created, violation journalled; orchestrator passes the gate as sole
  writer. 24/24 green on the :8901 clone with real cognition.

Authority gate holds independent of daemon write-health (proven with daemon
both alive and, earlier, crashed). Prod :8742 untouched.

lang/swarm/containment.el

@@ -21,8 +21,19 @@
 
 // ── Token minting ────────────────────────────────────────────────────────────
 
-// containment_coordinator_token — the token a coordinator holds. Depth 0.
-// Only a coordinator token may open a swarm.
+// CAPABILITIES. A scope token carries a `caps` set — the authority it holds.
+// This is an AUTHORITY gate, not a health gate: capability is decided at mint
+// time and cannot be acquired at runtime. Engram-WRITE (op_write/op_relate/
+// op_supersede -> POST /api/nodes, /api/edges, DELETE) and dharma_emit are
+// @manager-ONLY capabilities — exactly the VBD rule that only the orchestrator
+// mutates global state. The orchestrator's token carries them; a worker's token
+// NEVER does. A worker is therefore STRUCTURALLY UNABLE to mutate global engram
+// state, regardless of engram health.
+fn cap_orchestrator() -> String { return "engram:read,engram:write,dharma:emit,state:write" }
+fn cap_worker() -> String { return "engram:read" }
+
+// containment_coordinator_token — the token the orchestrator (@manager) holds.
+// Depth 0. Carries the engram-WRITE + dharma-emit capabilities (@manager-only).
 fn containment_coordinator_token(corr_id: String) -> String {
     let kv: [String] = el_list_empty()
     let kv = el_list_append(kv, "kind")
@@ -33,11 +44,15 @@ fn containment_coordinator_token(corr_id: String) -> String {
     let kv = el_list_append(kv, "")
     let kv = el_list_append(kv, "depth")
     let kv = el_list_append(kv, "0")
+    let kv = el_list_append(kv, "caps")
+    let kv = el_list_append(kv, cap_orchestrator())
     return json_build_object(kv)
 }
 
 // containment_worker_token — the token stamped into a worker's envelope. Depth 1.
-// A worker token is a closed boundary: holding it forbids opening/joining swarms.
+// A closed boundary: forbids opening/joining swarms AND carries ONLY the
+// engram:READ capability — no engram:write, no dharma:emit. Read-only against the
+// full engram; may write only its own local geometry (its returned result).
 fn containment_worker_token(corr_id: String, worker_id: String) -> String {
     let kv: [String] = el_list_empty()
     let kv = el_list_append(kv, "kind")
@@ -48,9 +63,16 @@ fn containment_worker_token(corr_id: String, worker_id: String) -> String {
     let kv = el_list_append(kv, worker_id)
     let kv = el_list_append(kv, "depth")
     let kv = el_list_append(kv, "1")
+    let kv = el_list_append(kv, "caps")
+    let kv = el_list_append(kv, cap_worker())
     return json_build_object(kv)
 }
 
+// containment_has_cap — does this token carry capability `cap`?
+fn containment_has_cap(token: String, cap: String) -> Bool {
+    return str_contains(json_get_string(token, "caps"), cap)
+}
+
 // ── Rule checks (return "" on allow, or a rejection reason string) ───────────
 
 // containment_check_open — may the holder of `token` OPEN a new swarm?
@@ -97,6 +119,28 @@ fn containment_check_lateral(from_token: String, to_worker_id: String) -> String
     return ""
 }
 
+// containment_check_engram_write — RULE 4: only a token carrying the
+// engram:write capability (the orchestrator's) may mutate global engram state.
+// A worker token (engram:read only) is REJECTED — the authority gate. Reuses the
+// exact scope-token mechanism as Rule 2's open-denial. Returns "" on allow, or a
+// rejection reason. This is an AUTHORITY gate: it does not consult engram health.
+fn containment_check_engram_write(token: String, op: String) -> String {
+    if containment_has_cap(token, "engram:write") {
+        return ""
+    }
+    return "CONTAINMENT rule 4: engram-write is @manager-only — a worker is read-only against the engram and may not mutate global state (op=" + op + " kind=" + json_get_string(token, "kind") + " worker=" + json_get_string(token, "worker") + " caps=" + json_get_string(token, "caps") + ")"
+}
+
+// containment_check_dharma_emit — the same @manager-only rule for dharma_emit,
+// grounding Rule 4 in VBD: global-state mutations (engram-write, dharma-emit) are
+// orchestrator-only, checked by the one capability mechanism.
+fn containment_check_dharma_emit(token: String) -> String {
+    if containment_has_cap(token, "dharma:emit") {
+        return ""
+    }
+    return "CONTAINMENT rule 4: dharma_emit is @manager-only (kind=" + json_get_string(token, "kind") + ")"
+}
+
 // ── Enforcement helpers ──────────────────────────────────────────────────────
 
 // containment_allows_open — Bool convenience over containment_check_open.
@@ -121,3 +165,17 @@ fn containment_guard_open(token: String, corr_id: String) -> String {
     worktrack_append("containment.violation", corr_id, "open", p)
     return reason
 }
+
+// containment_guard_engram_write — assert a token may mutate global engram state
+// (Rule 4). Returns "" if allowed; otherwise journals a containment.violation and
+// returns the reason. The write path MUST abort on a non-empty return.
+fn containment_guard_engram_write(token: String, corr_id: String, op: String) -> String {
+    let reason: String = containment_check_engram_write(token, op)
+    if str_eq(reason, "") {
+        return ""
+    }
+    let p0: String = json_set_str("{}", "reason", reason)
+    let p1: String = json_set_str(p0, "op", op)
+    worktrack_append("containment.violation", corr_id, "engram-write", p1)
+    return reason
+}