diff --git a/SESSION_LOG.md b/SESSION_LOG.md
index eb329d2..d66ce44 100644
--- a/SESSION_LOG.md
+++ b/SESSION_LOG.md
@@ -1,6 +1,7 @@
 # Session Log – zlh-grind
 
-Append-only execution log for GPT working in ZeroLagHub environment.
+Append-only execution log for GPT-assisted development work.  
+Do not rewrite or reorder past entries.
 
 ---
 
@@ -37,3 +38,49 @@ Append-only execution log for GPT working in ZeroLagHub environment.
 - Treat `container_type` as the canonical wire key until the next planned template rev.
 
 ---
+
+## 2025-12-21
+- Goal: Restore reliable end-to-end provisioning for devcontainers and agent-managed installs.
+- Observed repeated failures during devcontainer runtime installation (node, python, go, java).
+- Initial assumption was installer regression; investigation showed installers were enforcing contract correctly.
+- Root cause identified: agent was not exporting required runtime environment variables (notably `RUNTIME_VERSION`).
+
+### Devcontainer provisioning investigation
+- Deep dive on zlh-agent devcontainer provisioning flow.
+- Confirmed that all devcontainer installers intentionally require `RUNTIME_VERSION` and fail fast if missing.
+- Clarified that payload JSON is not read by installers; agent must project intent via environment variables.
+- Verified that installer logic itself (artifact naming, extraction, symlink layout) was correct.
+
+### Embedded installer execution findings
+- Agent executes installers as **embedded scripts**, not filesystem paths.
+- Identified critical requirement: shared installer logic (`common.sh`) and runtime installer must execute in the **same shell session**.
+- Failure mode observed: `install_runtime: command not found` → caused by running runtime installer without `common.sh` loaded.
+- Confirmed this explains missing runtime directories and lack of artifact downloads.
+
+### Installer architecture changes
+- Refactored installer model to:
+  - `common.sh`: shared, strict, embedded-safe installation logic
+  - per-runtime installers (`node`, `python`, `go`, `java`) as declarative descriptors only
+- Established that runtime installers are intentionally minimal and declarative by design.
+- Confirmed that this preserves existing runtime layout:
+  `/opt/zlh/runtime/<language>/<version>/current`
+
+### Artifact layout update
+- Artifact naming and layout standardized to simplified form:
+  - `node-24.tar.xz`
+  - `python-3.12.tar.xz`
+  - `go-1.22.tar.gz`
+  - `jdk-21.tar.gz`
+- Identified mismatch between runtime name and archive prefix (notably Java).
+- Introduced `ARCHIVE_PREFIX` as a runtime-level variable to resolve naming cleanly.
+
+### Final conclusions
+- No regression in installer logic; failures were execution-order and environment-projection issues.
+- Correct fix is agent-side:
+  - concatenate `common.sh` + runtime installer into one bash invocation
+  - inject `RUNTIME_VERSION` (and related vars) into environment
+- Architecture now supports deterministic, artifact-driven, embedded-safe installs.
+
+Status: **Root cause resolved; implementation pending agent patch & installer updates.**
+
+---