diff --git a/docs/milestones/M09/M09_plan.md b/docs/milestones/M09/M09_plan.md
index 34795560a..2faf52705 100644
--- a/docs/milestones/M09/M09_plan.md
+++ b/docs/milestones/M09/M09_plan.md
@@ -1,3 +1,255 @@
-# M09 Plan — Execution Context Seam
+# M09 Plan — Execution Context Introduction
 
-(To be populated.)
+Project: **Serena**
+Phase: **Phase II — Runtime Seam Preparation**
+Milestone: **M09**
+Title: **Execution Context Introduction**
+
+Branch: `m09-execution-context`
+
+---
+
+## 1. Intent / Target
+
+M08 migrated runtime reads from `shared.opts` to `p.opts_snapshot` inside the generation pipeline.
+
+However the runtime still depends heavily on **global shared state**:
+
+- `shared.sd_model`
+- `shared.device`
+- `shared.state`
+- `shared.cmd_opts`
+
+These globals prevent the generation pipeline from becoming a **testable runtime component**.
+
+The goal of **M09** is to introduce a **lightweight runtime execution context** that groups these runtime dependencies together.
+
+Example concept:
+
+```python
+RuntimeContext(
+    model,
+    opts_snapshot,
+    device,
+    state,
+    cmd_opts
+)
+```
+
+The context will be **attached to the processing object** but will **not yet replace global state everywhere**.
+
+This milestone introduces the seam without changing behavior.
+
+---
+
+## 2. Scope Boundaries
+
+### In Scope
+
+Create a new runtime structure:
+
+```
+modules/runtime_context.py
+```
+
+Define `RuntimeContext` with fields:
+
+- `model`
+- `opts_snapshot`
+- `device`
+- `state`
+- `cmd_opts`
+
+Attach it during generation:
+
+```
+p.runtime_context
+```
+
+Initial wiring occurs in `process_images_inner()`:
+
+```python
+p.runtime_context = RuntimeContext(
+    model=shared.sd_model,
+    opts_snapshot=p.opts_snapshot,
+    device=shared.device,
+    state=shared.state,
+    cmd_opts=shared.cmd_opts,
+)
+```
+
+Place this **after snapshot creation**.
+
+### Out of Scope
+
+M09 must **NOT**:
+
+- remove `shared.sd_model`
+- remove `shared.device`
+- modify extension interfaces
+- change sampling behavior
+- change API responses
+- refactor the sampler pipeline
+
+The context exists **in parallel with shared state** for now.
+
+---
+
+## 3. Invariants
+
+The following must remain identical.
+
+| Invariant | Description |
+|-----------|-------------|
+| Generation determinism | Same inputs → same outputs |
+| Sampling math | No changes to samplers or conditioning |
+| File outputs | Paths and naming unchanged |
+| Extension compatibility | Extensions must still use `shared.*` |
+| API behavior | txt2img/img2img responses unchanged |
+| CLI behavior | No change to CLI flags |
+
+---
+
+## 4. Verification Plan
+
+CI gates must remain green.
+
+| Check | Requirement |
+|-------|-------------|
+| Linter | Pass |
+| Smoke tests | Pass |
+| Quality tests | Pass |
+| Coverage | ≥ 40% |
+
+Local verification:
+
+```
+pytest test/smoke
+pytest test/quality
+```
+
+Manual checks:
+
+- txt2img generation
+- img2img generation
+- highres fix
+- image saving
+- grid saving
+
+---
+
+## 5. Implementation Steps
+
+### Step 1 — Create runtime context module
+
+Create file: `modules/runtime_context.py`
+
+```python
+from dataclasses import dataclass
+
+@dataclass
+class RuntimeContext:
+    model: object
+    opts_snapshot: object
+    device: object
+    state: object
+    cmd_opts: object
+```
+
+### Step 2 — Attach context to processing object
+
+Modify: `modules/processing.py`
+
+Inside `process_images_inner()`, after snapshot creation:
+
+```python
+from modules.runtime_context import RuntimeContext
+
+p.runtime_context = RuntimeContext(
+    model=shared.sd_model,
+    opts_snapshot=p.opts_snapshot,
+    device=shared.device,
+    state=shared.state,
+    cmd_opts=shared.cmd_opts,
+)
+```
+
+### Step 3 — No migration yet
+
+Do **NOT** change runtime reads yet.
+
+For example this must remain:
+
+```python
+shared.sd_model
+shared.device
+```
+
+The context is introduced but **not yet consumed**.
+
+---
+
+## 6. Risk & Rollback Plan
+
+Risk level: **Very low**
+
+Changes introduce a new object but do not change runtime behavior.
+
+| Risk | Mitigation |
+|------|------------|
+| Missing import | CI smoke tests |
+| Attribute collision | Use `runtime_context` name |
+
+Rollback: `git revert milestone commit`
+
+---
+
+## 7. Deliverables
+
+Expected code changes:
+
+- `modules/runtime_context.py` (new)
+- `modules/processing.py` (modified)
+
+Documentation artifacts:
+
+- `docs/milestones/M09/M09_plan.md`
+- `docs/milestones/M09/M09_toolcalls.md`
+
+---
+
+## 8. Expected Outcome
+
+After M09 the generation runtime will expose `p.runtime_context` which groups:
+
+- `model`
+- `opts_snapshot`
+- `device`
+- `state`
+- `cmd_opts`
+
+The runtime seam stack becomes:
+
+```
+temporary_opts()             M05
+prepare_prompt_seed_state()  M06
+opts snapshot                M07
+snapshot threading           M08
+execution context            M09
+```
+
+This completes **Phase II runtime seam preparation**.
+
+---
+
+## 9. Success Criteria
+
+M09 is complete when:
+
+- [ ] Runtime context introduced
+- [ ] Context attached to processing object
+- [ ] CI fully green
+- [ ] No behavior change
+- [ ] Milestone artifacts generated
+- [ ] Ledger updated
+- [ ] Tag created: `v0.0.09-m09`
diff --git a/docs/milestones/M09/M09_toolcalls.md b/docs/milestones/M09/M09_toolcalls.md
index 1c2f1f788..0c39211fd 100644
--- a/docs/milestones/M09/M09_toolcalls.md
+++ b/docs/milestones/M09/M09_toolcalls.md
@@ -2,4 +2,7 @@
 
 Implementation toolcalls for Cursor execution.
 
-(To be filled during milestone execution.)
+| Timestamp | Tool | Purpose | Files/Target | Status |
+|-----------|------|---------|--------------|--------|
+| 2026-03-11 | write | Populate M09_plan.md with full plan | docs/milestones/M09/M09_plan.md | completed |
+| 2026-03-11 | run | git checkout main, pull, create branch | git | pending |