diff --git a/docs/Architecture-Build-Spec.md b/docs/Architecture-Build-Spec.md
index 54e8b71..9c43c9a 100644
--- a/docs/Architecture-Build-Spec.md
+++ b/docs/Architecture-Build-Spec.md
@@ -622,6 +622,56 @@ rests on.
 **Deferred:** the operator-writable procedures collection. The interface is defined
 here; the content and the C2 binding list arrive with the policy taxonomy (Part H).
 
+**Concrete mapping onto Outline.** Observed in the running instance: a **collection**
+carries per-user permissions with three tiers — visible-to (read), read-write, and
+manager. Permissions are collection-scoped, not per-document.
+- Therefore **one collection per writing principal**, with read membership granted to
+  everyone else who needs it: `nisse-ops-world` (write: `nisse-ops`),
+  `nisse-dev-world` (write: `nisse-dev`), `procedures` (write: operator).
+- **What this enforces, precisely:** no *other agent* can write a given agent's world
+  model — the collision that would otherwise be silent and unattributable. It does not
+  enforce operator-versus-agent exclusion, because the operator holds manager on their
+  own wiki and can always grant themselves write. That half is procedural: the
+  break-glass routine stops the agents first, so concurrent writers do not exist while
+  editing.
+- **Assign per user, not per group.** Outline groups appear to be internal to Outline
+  rather than federated with LLDAP (A8), so using them would put membership in a second
+  place that nothing syncs. With three principals the manual mapping is trivial and
+  obvious; revisit only if the cast grows.
+- **Each agent's API token must belong to that agent's own Outline user.** Outline API
+  keys are per-user, so the token *is* the identity every permission above evaluates
+  against. A token minted from the operator's account — or an admin's — silently voids
+  the entire boundary while appearing to work.
+- **Identify collections and documents by ID, from config and state.** Collection IDs
+  come from env (`NISSE_OUTLINE_*_COLLECTION`), never discovered from "whatever the
+  token can write": a permission change must not silently redefine what an agent
+  considers its own. Document IDs are recorded in the state store (A2) when created and
+  used for updates, which also makes writing idempotent — a retry after a crash updates
+  the document instead of creating a second one.
+- **Revision reads, not conditional writes.** Because break-glass stops the agents,
+  compare-and-swap is unnecessary; what is needed is the ability to *observe* that a
+  document changed since the agent last read it, feeding the A3 divergence check.
+  Whether Outline exposes a revision identifier or only a modified timestamp is
+  unverified — either satisfies this.
+
+#### Considered and deferred: Outline's MCP server
+
+Outline can expose search, read, create and edit over MCP (remote, Streamable HTTP,
+enabled workspace-wide). **Not adopted for the retrieval path**, because A17's
+enforcement depends on this library sitting *between* the model and the store: staleness
+marking, snapshotting into the canonical log, binding procedures to action classes, and
+gating a failed confirm-first read all happen to a retrieval before the model sees it.
+MCP's purpose is the opposite — direct model access — and a procedure the model may
+decline to fetch does not constrain it (A12).
+
+It remains a reasonable candidate for the *discretionary* search tool later, and unlike
+the vendor agent SDKs A13 rejects, MCP is a neutral standard rather than lock-in: one
+client would serve many servers if others are ever added. Before adopting it, verify
+that it honours the key owner's **collection** permissions rather than mere workspace
+membership, and that the workspace-level toggle does not force broader exposure than
+intended.
+
+
 ---
 
 ## PART B — THE DEV AGENT / `nisse-dev` (build first)