docs: record V2 session-relative memory permission

Describe the OpenCode 2 FileAccess.resolve behavior and the deliberate
divergence from Codex, which rebinds the consolidator cwd and managed
sandbox to the memory root instead.

Refs #7

Author: moritzfl

ARCHITECTURE.md

@@ -203,7 +203,13 @@ differs by host:
 - **OpenCode2:** V2 agents are location-scoped, so helpers spawn in the
   active plugin location (`setSubSessionDirectory`). Session boundary is the
   project; path permissions scope `read`/`edit` + `external_directory` to the
-  memory workspace. `glob`/`grep` permissions match search patterns, so V2
+  memory workspace. OpenCode 2 asserts a session-relative resource when the
+  target is inside the session or project directory, so the helper session
+  also allows that posix-relative form of its one root. When the helper runs
+  at or inside the root, relative grants exclude normalized traversal above
+  that root and absolute paths outside it. `external_directory` grants remain
+  absolute. Memory remains global. `glob`/`grep` permissions match
+  search patterns, so V2
   wraps their built-in executors to validate paths against the helper's one
   session-granted memory root, defaulting relative searches to that root.
   Helper creation supplies session-scoped deny-first rules that narrow access

codex-map.yaml

@@ -391,6 +391,13 @@ mappings:
       upstream is not emitted (no plugin telemetry backend). OpenCode helper
       permissions restrict each job to its own memory root even in dual mode;
       V1 uses session external_directory rules, V2 uses session deny-first rules.
+      DELIBERATE DIVERGENCE (OpenCode 2.0.18 FileAccess.resolve): in-tree targets
+      are asserted as session-relative resources, so V2 helper rules also allow
+      the posix-relative form of that one memory root, including helpers at or
+      inside it, with normalized parent escapes denied. external_directory
+      grants remain absolute. Codex instead rebinds the consolidator cwd and
+      managed sandbox to the memory root; these string rules adapt OpenCode's
+      permission API without changing global memory scope.
   - ours: src/workspace.ts
     theirs: codex-rs/memories/write/src/storage.rs
     note: >