diff --git a/checkpoint.json b/checkpoint.json
index 278ff9174..c5758fe27 100644
--- a/checkpoint.json
+++ b/checkpoint.json
@@ -1,33 +1,40 @@
 {
-  "timestamp": "2026-03-16T02:00:22.109258Z",
-  "current_node": "preflight_lint",
+  "timestamp": "2026-03-16T02:04:28.578690Z",
+  "current_node": "implement",
   "completed_nodes": [
     "start",
     "toolchain",
     "preflight_compile",
-    "preflight_lint"
+    "preflight_lint",
+    "implement"
   ],
   "node_retries": {
     "preflight_compile": 1,
     "start": 1,
     "preflight_lint": 1,
+    "implement": 1,
     "toolchain": 1
   },
   "context_values": {
+    "internal.retry_count.implement": 1,
+    "thread.preflight_lint.current_node": "implement",
+    "last_response": "Everything looks correct. Here's a summary of what was done:\n\n## Changes Made\n\n**File:** `lib/crates/fabro-workflows/src/cli/backend.rs`\n\n### 1. Extracted `track_file_event` helper function (lines 33",
     "internal.run_id": "01KKT5VYJ8FG6KX44AVXK8PY96",
     "outcome": "success",
-    "current.preamble": "Goal: # Fix: Sub-agent file writes not tracked in API backend\n\n## Context\n\nWhen the API backend's agent spawns sub-agents that call `edit_file`/`write_file`, those files are missing from `outcome.files_touched`. This causes downstream nodes (like `simplify_opus`) to receive an incomplete file list in their prompt preamble.\n\nRoot cause: `spawn_event_forwarder` in `backend.rs` only matches top-level `ToolCallStarted`/`ToolCallCompleted` events. Sub-agent tool calls arrive wrapped as `AgentEvent::SubAgentEvent { event: Box<inner> }` and hit the `_ => {}` catch-all.\n\n## Plan\n\n**Single file change:** `lib/crates/fabro-workflows/src/cli/backend.rs`\n\nIn `spawn_event_forwarder` (line 51), replace the flat match with a helper that recursively unwraps `SubAgentEvent` to extract the inner `ToolCallStarted`/`ToolCallCompleted`:\n\n```\nmatch &event.event {\n    AgentEvent::ToolCallStarted { .. } => { /* existing logic */ }\n    AgentEvent::ToolCallCompleted { .. } => { /* existing logic */ }\n+   AgentEvent::SubAgentEvent { event: inner, .. } => {\n+       // Recursively extract file-tracking events from sub-agents\n+       track_file_event(inner, &pending_tool_calls, &files_touched, &last_file_touched);\n+   }\n    _ => {}\n}\n```\n\nExtract the file-tracking logic into a `track_file_event(event, pending, touched, last)` function that:\n1. Matches `ToolCallStarted` for `write_file`/`edit_file` → records to `pending_tool_calls`\n2. Matches `ToolCallCompleted` (non-error) → moves from pending to `files_touched`\n3. Matches `SubAgentEvent` → recurses into the inner event (handles sub-sub-agents)\n4. Otherwise → no-op\n\nThe existing inline match in `spawn_event_forwarder` calls `track_file_event` for both top-level and sub-agent events.\n\n## Verification\n\n1. `cargo test -p fabro-workflows` — existing tests pass\n2. `cargo clippy --workspace -- -D warnings` — clean\n3. Add a unit test: emit a `SubAgentEvent` wrapping a `ToolCallStarted`/`ToolCallCompleted` for `edit_file`, verify it appears in `files_touched`\n\n\n## Completed stages\n- **toolchain**: success\n  - Script: `command -v cargo >/dev/null || { curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y && sudo ln -sf $HOME/.cargo/bin/* /usr/local/bin/; }; cargo --version 2>&1`\n  - Stdout:\n    ```\n    cargo 1.94.0 (85eff7c80 2026-01-15)\n    ```\n  - Stderr: (empty)\n- **preflight_compile**: success\n  - Script: `cargo check -q --workspace 2>&1`\n  - Stdout: (empty)\n  - Stderr: (empty)\n",
+    "current.preamble": "Goal: # Fix: Sub-agent file writes not tracked in API backend\n\n## Context\n\nWhen the API backend's agent spawns sub-agents that call `edit_file`/`write_file`, those files are missing from `outcome.files_touched`. This causes downstream nodes (like `simplify_opus`) to receive an incomplete file list in their prompt preamble.\n\nRoot cause: `spawn_event_forwarder` in `backend.rs` only matches top-level `ToolCallStarted`/`ToolCallCompleted` events. Sub-agent tool calls arrive wrapped as `AgentEvent::SubAgentEvent { event: Box<inner> }` and hit the `_ => {}` catch-all.\n\n## Plan\n\n**Single file change:** `lib/crates/fabro-workflows/src/cli/backend.rs`\n\nIn `spawn_event_forwarder` (line 51), replace the flat match with a helper that recursively unwraps `SubAgentEvent` to extract the inner `ToolCallStarted`/`ToolCallCompleted`:\n\n```\nmatch &event.event {\n    AgentEvent::ToolCallStarted { .. } => { /* existing logic */ }\n    AgentEvent::ToolCallCompleted { .. } => { /* existing logic */ }\n+   AgentEvent::SubAgentEvent { event: inner, .. } => {\n+       // Recursively extract file-tracking events from sub-agents\n+       track_file_event(inner, &pending_tool_calls, &files_touched, &last_file_touched);\n+   }\n    _ => {}\n}\n```\n\nExtract the file-tracking logic into a `track_file_event(event, pending, touched, last)` function that:\n1. Matches `ToolCallStarted` for `write_file`/`edit_file` → records to `pending_tool_calls`\n2. Matches `ToolCallCompleted` (non-error) → moves from pending to `files_touched`\n3. Matches `SubAgentEvent` → recurses into the inner event (handles sub-sub-agents)\n4. Otherwise → no-op\n\nThe existing inline match in `spawn_event_forwarder` calls `track_file_event` for both top-level and sub-agent events.\n\n## Verification\n\n1. `cargo test -p fabro-workflows` — existing tests pass\n2. `cargo clippy --workspace -- -D warnings` — clean\n3. Add a unit test: emit a `SubAgentEvent` wrapping a `ToolCallStarted`/`ToolCallCompleted` for `edit_file`, verify it appears in `files_touched`\n\n\n## Completed stages\n- **toolchain**: success\n  - Script: `command -v cargo >/dev/null || { curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y && sudo ln -sf $HOME/.cargo/bin/* /usr/local/bin/; }; cargo --version 2>&1`\n  - Stdout:\n    ```\n    cargo 1.94.0 (85eff7c80 2026-01-15)\n    ```\n  - Stderr: (empty)\n- **preflight_compile**: success\n  - Script: `cargo check -q --workspace 2>&1`\n  - Stdout: (empty)\n  - Stderr: (empty)\n- **preflight_lint**: success\n  - Script: `cargo clippy -q --workspace -- -D warnings 2>&1`\n  - Stdout: (empty)\n  - Stderr: (empty)\n",
     "command.stderr": "",
     "graph.model_stylesheet": "\n            * { backend: api; model: claude-opus-4-6;}\n        ",
     "internal.fidelity": "compact",
-    "internal.thread_id": "preflight_compile",
+    "response.implement": "Everything looks correct. Here's a summary of what was done:\n\n## Changes Made\n\n**File:** `lib/crates/fabro-workflows/src/cli/backend.rs`\n\n### 1. Extracted `track_file_event` helper function (lines 33–75)\n\nA new recursive function that handles file-tracking logic for `write_file`/`edit_file` tool calls:\n- **`ToolCallStarted`** → records the `file_path` argument in `pending_tool_calls` keyed by `tool_call_id`\n- **`ToolCallCompleted`** (non-error) → moves the path from `pending_tool_calls` to `files_touched` and updates `last_file_touched`\n- **`ToolCallCompleted`** (error) → removes from `pending_tool_calls` without recording\n- **`SubAgentEvent`** → recursively unwraps the inner event and calls itself (handles arbitrarily nested sub-agents)\n- Everything else → no-op\n\n### 2. Refactored `spawn_event_forwarder` to use `track_file_event`\n\nReplaced the inline `match` block with a single call to `track_file_event(&event.event, ...)`, which now handles both top-level and sub-agent events.\n\n### 3. Added 4 unit tests\n\n- `track_file_event_records_top_level_write` — verifies basic `write_file` tracking still works\n- `track_file_event_unwraps_sub_agent_edit` — verifies `SubAgentEvent`-wrapped `edit_file` calls are tracked\n- `track_file_event_unwraps_nested_sub_sub_agent` — verifies double-nested `SubAgentEvent` (sub-sub-agent) is handled\n- `track_file_event_error_removes_pending` — verifies errored sub-agent tool calls don't pollute `files_touched`\n\n### Verification\n- ✅ `cargo test -p fabro-workflows` — 179 passed, 0 failed\n- ✅ `cargo clippy --workspace -- -D warnings` — clean",
+    "last_stage": "implement",
+    "internal.thread_id": "preflight_lint",
     "thread.start.current_node": "toolchain",
     "command.output": "",
     "graph.goal": "# Fix: Sub-agent file writes not tracked in API backend\n\n## Context\n\nWhen the API backend's agent spawns sub-agents that call `edit_file`/`write_file`, those files are missing from `outcome.files_touched`. This causes downstream nodes (like `simplify_opus`) to receive an incomplete file list in their prompt preamble.\n\nRoot cause: `spawn_event_forwarder` in `backend.rs` only matches top-level `ToolCallStarted`/`ToolCallCompleted` events. Sub-agent tool calls arrive wrapped as `AgentEvent::SubAgentEvent { event: Box<inner> }` and hit the `_ => {}` catch-all.\n\n## Plan\n\n**Single file change:** `lib/crates/fabro-workflows/src/cli/backend.rs`\n\nIn `spawn_event_forwarder` (line 51), replace the flat match with a helper that recursively unwraps `SubAgentEvent` to extract the inner `ToolCallStarted`/`ToolCallCompleted`:\n\n```\nmatch &event.event {\n    AgentEvent::ToolCallStarted { .. } => { /* existing logic */ }\n    AgentEvent::ToolCallCompleted { .. } => { /* existing logic */ }\n+   AgentEvent::SubAgentEvent { event: inner, .. } => {\n+       // Recursively extract file-tracking events from sub-agents\n+       track_file_event(inner, &pending_tool_calls, &files_touched, &last_file_touched);\n+   }\n    _ => {}\n}\n```\n\nExtract the file-tracking logic into a `track_file_event(event, pending, touched, last)` function that:\n1. Matches `ToolCallStarted` for `write_file`/`edit_file` → records to `pending_tool_calls`\n2. Matches `ToolCallCompleted` (non-error) → moves from pending to `files_touched`\n3. Matches `SubAgentEvent` → recurses into the inner event (handles sub-sub-agents)\n4. Otherwise → no-op\n\nThe existing inline match in `spawn_event_forwarder` calls `track_file_event` for both top-level and sub-agent events.\n\n## Verification\n\n1. `cargo test -p fabro-workflows` — existing tests pass\n2. `cargo clippy --workspace -- -D warnings` — clean\n3. Add a unit test: emit a `SubAgentEvent` wrapping a `ToolCallStarted`/`ToolCallCompleted` for `edit_file`, verify it appears in `files_touched`\n",
     "internal.retry_count.start": 1,
     "internal.retry_count.preflight_compile": 1,
     "graph.rankdir": "LR",
-    "current_node": "preflight_lint",
+    "current_node": "implement",
     "internal.retry_count.toolchain": 1,
     "failure_class": "",
     "thread.preflight_compile.current_node": "preflight_lint",
@@ -38,6 +45,28 @@
   },
   "logs": [],
   "node_outcomes": {
+    "implement": {
+      "status": "success",
+      "context_updates": {
+        "last_response": "Everything looks correct. Here's a summary of what was done:\n\n## Changes Made\n\n**File:** `lib/crates/fabro-workflows/src/cli/backend.rs`\n\n### 1. Extracted `track_file_event` helper function (lines 33",
+        "response.implement": "Everything looks correct. Here's a summary of what was done:\n\n## Changes Made\n\n**File:** `lib/crates/fabro-workflows/src/cli/backend.rs`\n\n### 1. Extracted `track_file_event` helper function (lines 33–75)\n\nA new recursive function that handles file-tracking logic for `write_file`/`edit_file` tool calls:\n- **`ToolCallStarted`** → records the `file_path` argument in `pending_tool_calls` keyed by `tool_call_id`\n- **`ToolCallCompleted`** (non-error) → moves the path from `pending_tool_calls` to `files_touched` and updates `last_file_touched`\n- **`ToolCallCompleted`** (error) → removes from `pending_tool_calls` without recording\n- **`SubAgentEvent`** → recursively unwraps the inner event and calls itself (handles arbitrarily nested sub-agents)\n- Everything else → no-op\n\n### 2. Refactored `spawn_event_forwarder` to use `track_file_event`\n\nReplaced the inline `match` block with a single call to `track_file_event(&event.event, ...)`, which now handles both top-level and sub-agent events.\n\n### 3. Added 4 unit tests\n\n- `track_file_event_records_top_level_write` — verifies basic `write_file` tracking still works\n- `track_file_event_unwraps_sub_agent_edit` — verifies `SubAgentEvent`-wrapped `edit_file` calls are tracked\n- `track_file_event_unwraps_nested_sub_sub_agent` — verifies double-nested `SubAgentEvent` (sub-sub-agent) is handled\n- `track_file_event_error_removes_pending` — verifies errored sub-agent tool calls don't pollute `files_touched`\n\n### Verification\n- ✅ `cargo test -p fabro-workflows` — 179 passed, 0 failed\n- ✅ `cargo clippy --workspace -- -D warnings` — clean",
+        "last_stage": "implement"
+      },
+      "notes": "Stage completed: implement",
+      "usage": {
+        "model": "claude-opus-4-6",
+        "input_tokens": 23355,
+        "output_tokens": 7498,
+        "cache_read_tokens": 535214,
+        "cache_write_tokens": 28496,
+        "reasoning_tokens": 43,
+        "cost": 0.912675
+      },
+      "files_touched": [
+        "/home/daytona/workspace/lib/crates/fabro-workflows/src/cli/backend.rs"
+      ],
+      "duration_ms": 244188
+    },
     "preflight_lint": {
       "status": "success",
       "context_updates": {
@@ -70,8 +99,9 @@
       "duration_ms": 69914
     }
   },
-  "next_node_id": "implement",
+  "next_node_id": "simplify_opus",
   "node_visits": {
+    "implement": 1,
     "preflight_compile": 1,
     "preflight_lint": 1,
     "toolchain": 1,
diff --git a/nodes/implement/prompt.md b/nodes/implement/prompt.md
new file mode 100644
index 000000000..1cd997f43
--- /dev/null
+++ b/nodes/implement/prompt.md
@@ -0,0 +1,60 @@
+Goal: # Fix: Sub-agent file writes not tracked in API backend
+
+## Context
+
+When the API backend's agent spawns sub-agents that call `edit_file`/`write_file`, those files are missing from `outcome.files_touched`. This causes downstream nodes (like `simplify_opus`) to receive an incomplete file list in their prompt preamble.
+
+Root cause: `spawn_event_forwarder` in `backend.rs` only matches top-level `ToolCallStarted`/`ToolCallCompleted` events. Sub-agent tool calls arrive wrapped as `AgentEvent::SubAgentEvent { event: Box<inner> }` and hit the `_ => {}` catch-all.
+
+## Plan
+
+**Single file change:** `lib/crates/fabro-workflows/src/cli/backend.rs`
+
+In `spawn_event_forwarder` (line 51), replace the flat match with a helper that recursively unwraps `SubAgentEvent` to extract the inner `ToolCallStarted`/`ToolCallCompleted`:
+
+```
+match &event.event {
+    AgentEvent::ToolCallStarted { .. } => { /* existing logic */ }
+    AgentEvent::ToolCallCompleted { .. } => { /* existing logic */ }
++   AgentEvent::SubAgentEvent { event: inner, .. } => {
++       // Recursively extract file-tracking events from sub-agents
++       track_file_event(inner, &pending_tool_calls, &files_touched, &last_file_touched);
++   }
+    _ => {}
+}
+```
+
+Extract the file-tracking logic into a `track_file_event(event, pending, touched, last)` function that:
+1. Matches `ToolCallStarted` for `write_file`/`edit_file` → records to `pending_tool_calls`
+2. Matches `ToolCallCompleted` (non-error) → moves from pending to `files_touched`
+3. Matches `SubAgentEvent` → recurses into the inner event (handles sub-sub-agents)
+4. Otherwise → no-op
+
+The existing inline match in `spawn_event_forwarder` calls `track_file_event` for both top-level and sub-agent events.
+
+## Verification
+
+1. `cargo test -p fabro-workflows` — existing tests pass
+2. `cargo clippy --workspace -- -D warnings` — clean
+3. Add a unit test: emit a `SubAgentEvent` wrapping a `ToolCallStarted`/`ToolCallCompleted` for `edit_file`, verify it appears in `files_touched`
+
+
+## Completed stages
+- **toolchain**: success
+  - Script: `command -v cargo >/dev/null || { curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y && sudo ln -sf $HOME/.cargo/bin/* /usr/local/bin/; }; cargo --version 2>&1`
+  - Stdout:
+    ```
+    cargo 1.94.0 (85eff7c80 2026-01-15)
+    ```
+  - Stderr: (empty)
+- **preflight_compile**: success
+  - Script: `cargo check -q --workspace 2>&1`
+  - Stdout: (empty)
+  - Stderr: (empty)
+- **preflight_lint**: success
+  - Script: `cargo clippy -q --workspace -- -D warnings 2>&1`
+  - Stdout: (empty)
+  - Stderr: (empty)
+
+
+Read the plan file referenced in the goal and implement every step. Make all the code changes described in the plan. Use red/green TDD.
\ No newline at end of file
diff --git a/nodes/implement/provider_used.json b/nodes/implement/provider_used.json
new file mode 100644
index 000000000..c1905ff10
--- /dev/null
+++ b/nodes/implement/provider_used.json
@@ -0,0 +1,5 @@
+{
+  "mode": "agent",
+  "provider": "anthropic",
+  "model": "claude-opus-4-6"
+}
\ No newline at end of file
diff --git a/nodes/implement/response.md b/nodes/implement/response.md
new file mode 100644
index 000000000..65c6e1e86
--- /dev/null
+++ b/nodes/implement/response.md
@@ -0,0 +1,29 @@
+Everything looks correct. Here's a summary of what was done:
+
+## Changes Made
+
+**File:** `lib/crates/fabro-workflows/src/cli/backend.rs`
+
+### 1. Extracted `track_file_event` helper function (lines 33–75)
+
+A new recursive function that handles file-tracking logic for `write_file`/`edit_file` tool calls:
+- **`ToolCallStarted`** → records the `file_path` argument in `pending_tool_calls` keyed by `tool_call_id`
+- **`ToolCallCompleted`** (non-error) → moves the path from `pending_tool_calls` to `files_touched` and updates `last_file_touched`
+- **`ToolCallCompleted`** (error) → removes from `pending_tool_calls` without recording
+- **`SubAgentEvent`** → recursively unwraps the inner event and calls itself (handles arbitrarily nested sub-agents)
+- Everything else → no-op
+
+### 2. Refactored `spawn_event_forwarder` to use `track_file_event`
+
+Replaced the inline `match` block with a single call to `track_file_event(&event.event, ...)`, which now handles both top-level and sub-agent events.
+
+### 3. Added 4 unit tests
+
+- `track_file_event_records_top_level_write` — verifies basic `write_file` tracking still works
+- `track_file_event_unwraps_sub_agent_edit` — verifies `SubAgentEvent`-wrapped `edit_file` calls are tracked
+- `track_file_event_unwraps_nested_sub_sub_agent` — verifies double-nested `SubAgentEvent` (sub-sub-agent) is handled
+- `track_file_event_error_removes_pending` — verifies errored sub-agent tool calls don't pollute `files_touched`
+
+### Verification
+- ✅ `cargo test -p fabro-workflows` — 179 passed, 0 failed
+- ✅ `cargo clippy --workspace -- -D warnings` — clean
\ No newline at end of file
diff --git a/nodes/implement/status.json b/nodes/implement/status.json
new file mode 100644
index 000000000..b2517d54a
--- /dev/null
+++ b/nodes/implement/status.json
@@ -0,0 +1,6 @@
+{
+  "status": "success",
+  "notes": "Stage completed: implement",
+  "failure_reason": null,
+  "timestamp": "2026-03-16T02:04:28.577446+00:00"
+}
\ No newline at end of file