Reconcile session start guidance with Codex ownership model

SESSION_START.md

@@ -7,25 +7,37 @@ After reading `README.md`, use this checklist to start work.
 ## Required
 
 1. Review `OPEN_THREADS.md`
-2. Review `CONSTRAINTS.md`
+2. Review `Codex/README.md`
+3. Identify the owning repo for the task:
+   - `Codex/API/*`
+   - `Codex/Portal/*`
+   - `Codex/Agent/*`
+4. Review the relevant repo’s:
+   - `CURRENT_STATE.md`
+   - `OPEN_ITEMS.md`
+   - `DECISIONS.md`
+5. Review `CONSTRAINTS.md`
 
 ## Read If Relevant
 
-3. Review `PROJECT_CONTEXT.md` if current platform state or routing model matters
-4. Review `INFRASTRUCTURE.md` if VM, IP, or host context matters
-5. Review `UPSTREAMS.md` if other repos or external dependencies matter
+6. Review `PROJECT_CONTEXT.md` if current platform state or routing model matters
+7. Review `INFRASTRUCTURE.md` if VM, IP, host, or PBS context matters
+8. Review `UPSTREAMS.md` if other repos or external dependencies matter
 
 ## Deep Recovery Only
 
 Use these only if the live working set is not enough:
-
 - `SESSION_LOG/`
 - `Session_Summaries/`
 - `SCRATCH/`
 
 ## Final Check Before Working
 
-- Confirm no drift between portal, API, and agent assumptions
-- Confirm file model assumptions are accurate
-- Confirm upload transport is using raw piping
+- Confirm whether the task is repo-owned or cross-repo/platform-owned
+- Keep repo-specific work in the relevant `Codex/*` folder
+- Keep root `OPEN_THREADS.md` limited to active cross-repo/platform work
+- Remove completed items from `OPEN_ITEMS.md` instead of leaving them behind
+- Move durable implemented behavior into `CURRENT_STATE.md`
+- Move settled choices into `DECISIONS.md`
 - Never assume speculative features are implemented
+- Confirm upload transport is using raw piping where applicable