diff --git a/CLAUDE.md b/CLAUDE.md
index 2f68fde..70741a2 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -334,19 +334,26 @@ A clear comment at the declaration site is mandatory.
 
 ## On every session start
 
-Three active workstreams run in parallel — **IR** (the language compiler),
-**FFI** (Obj-C / JNI ceremony reduction), and **MEM** (memory module
-overhaul, mem.sx + protocol expansion). They touch mostly disjoint
-files; any can be advanced independently.
+Five active workstreams run in parallel — **IR** (the language compiler),
+**FFI** (Obj-C / JNI ceremony reduction), **MEM** (memory module
+overhaul, mem.sx + protocol expansion), **LANG** (user-facing language
+features — diagnostics renderer, heterogeneous variadic packs), and
+**ERR** (error handling: separate-channel `!` errors, `try` / `catch` /
+`or` / `errdefer`, return traces). They touch mostly disjoint files;
+any can be advanced independently.
 
-1. Read all three checkpoints to see where each stream is paused:
+1. Read all five checkpoints to see where each stream is paused:
    - `current/CHECKPOINT.md` — IR progress tracker.
    - `current/CHECKPOINT-FFI.md` — FFI progress tracker.
    - `current/CHECKPOINT-MEM.md` — MEM progress tracker + issues log.
+   - `current/CHECKPOINT-LANG.md` — LANG progress tracker.
+   - `current/CHECKPOINT-ERR.md` — ERR progress tracker.
 2. Read the plan that corresponds to the stream the user wants to advance:
    - `current/PLAN.md` — IR implementation plan.
    - `current/PLAN-FFI.md` — FFI ceremony reduction plan.
    - `~/.claude/plans/tidy-doodling-cray.md` — MEM (mem.sx) implementation plan.
+   - `current/PLAN-LANG.md` — LANG implementation plan.
+   - `current/PLAN-ERR.md` — ERR implementation plan.
 3. Read `specs.md` if you need to understand language behavior.
 4. Pick up from the next incomplete step in the relevant `CHECKPOINT*.md`.
    If the user hasn't said which stream to work on, ask before picking.
@@ -363,7 +370,9 @@ files; any can be advanced independently.
   probes/snippets there (e.g. `.sx-tmp/probe.sx`).
 - Work on **one step at a time**. Complete it fully before moving on.
 - After completing a step, immediately update the relevant checkpoint
-  (`current/CHECKPOINT.md` for IR, `current/CHECKPOINT-FFI.md` for FFI):
+  (`current/CHECKPOINT.md` for IR, `current/CHECKPOINT-FFI.md` for FFI,
+  `current/CHECKPOINT-MEM.md` for MEM, `current/CHECKPOINT-LANG.md` for
+  LANG, `current/CHECKPOINT-ERR.md` for ERR):
   - Update `## Last completed step` with the step you just finished.
   - Update `## Current state` with what exists now.
   - Update `## Next step` with what comes next.
@@ -526,6 +535,10 @@ Wiring a new bundling step:
 | `current/CHECKPOINT.md` | **Active** IR progress tracker. Update after every step. |
 | `current/PLAN-FFI.md` | **Active** FFI ceremony reduction plan (Obj-C / JNI intrinsics, JNI DSL, Obj-C header import). |
 | `current/CHECKPOINT-FFI.md` | **Active** FFI progress tracker. Update after every step. |
+| `current/PLAN-LANG.md` | **Active** LANG implementation plan (diagnostics renderer, heterogeneous variadic packs). |
+| `current/CHECKPOINT-LANG.md` | **Active** LANG progress tracker. Update after every step. |
+| `current/PLAN-ERR.md` | **Active** ERR implementation plan (`!` errors, `try` / `catch` / `or` / `errdefer`, return traces). |
+| `current/CHECKPOINT-ERR.md` | **Active** ERR progress tracker. Update after every step. |
 | `implementation_plan.md` | Archive of completed work (closures, protocols, etc.). Do not pick up tasks from here. |
 | `readme.md` | Original syntax sketches. Do not modify. |
 | `CLAUDE.md` | This file. Session instructions. |