diff --git a/AGENTS.md b/AGENTS.md
index 549cb082..832bddfc 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -12,6 +12,7 @@ All AI agents consuming this project must read `./conductor/workflow.md` and tre
 
 Detailed agent guidance lives in the following locations — read these directly, do not duplicate content here:
 
+- **MUST READ TO DE-RETARD EDIT WORKFLOW** `conductor/edit_workflow.md`
 - **Operational workflow:** `conductor/workflow.md`
 - **Code style and process:** `conductor/product-guidelines.md`
 - **Tech stack and constraints:** `conductor/tech-stack.md`
@@ -33,6 +34,39 @@ For understanding, using, and maintaining the tool, see `docs/Readme.md` and the
 - Do not skip TDD - write failing tests before implementation
 - Do not batch commits - commit per-task for atomic rollback
 - Do not add comments to source code; documentation lives in `/docs`
+- Do not use `set_file_slice` for multi-line content; it's literal line replacement by design (see `conductor/edit_workflow.md`)
+- Do not use `git restore` while a user is mid-conversation without first confirming the desired state
+
+## Session-Learned Anti-Patterns (Added 2026-06-07)
+
+These burned the most time in a recent startup_speedup session. The rules below are short because the rules above (and `conductor/edit_workflow.md`) are the source of truth.
+
+### 1. ALWAYS use the proper edit tool, not a custom script
+
+- For Python source edits, use `manual-slop_edit_file` with `old_string`/`new_string`. **Do NOT** write a standalone Python script that does file-level replacements.
+- Custom scripts fail silently on: wrong indent in `new_content`, wrong EOL (CRLF vs LF) in `old_string` searches, wrong exact-string match (whitespace drift).
+- When a script fails, debug the actual error message. Do not dismiss it and try a different approach.
+
+### 2. The decorator-orphan pitfall
+
+When inserting new methods **before an existing `@property` def**, your script will leave the `@property` decorator on the line above your new methods. The decorator then accidentally decorates YOUR new method (which is no longer a property, breaking any subsequent `@your_method.setter` calls). The file passes `ast.parse()` but blows up at import time.
+
+The fix: anchor on the **def line that has the `@property` ABOVE it**, and replace the pair `@property\n def foo(...)` with `@property\n def your_new(...)\n ...\n def foo(...)` — keeping the decorator attached to its original method. Or anchor on a different non-decorated landmark (e.g. `self._init_actions()`).
+
+### 3. `ast.parse()` "Syntax OK" is not enough
+
+`ast.parse()` only catches syntax errors. Semantic errors (wrong decorator targets, wrong class attribute, missing `self`, etc.) are NOT caught. After a multi-line edit, ALWAYS:
+- Import the module
+- Instantiate the class
+- Call the new method in the way it's expected to be called (e.g. `ctrl.foo_ts` vs `ctrl.foo_ts()` for properties vs methods)
+
+### 4. The "I'll just check git status" trap
+
+If you suspect you might have lost work, the worst move is to run `git status` / `git restore` while a frantic user is watching. Pause, read the actual file, and admit what state you're in. The user knows their state better than you do.
+
+### 5. Small, verified edits beat big scripts
+
+`conductor/edit_workflow.md` says it explicitly: 3-10 lines at a time, verify after each, repeat. If you find yourself writing a 200-line Python script to do an edit, you're doing it wrong. Use the MCP tools.
 
 ## Compaction Recovery
 
diff --git a/conductor/edit_workflow.md b/conductor/edit_workflow.md
index 9fd657d2..0fd98f32 100644
--- a/conductor/edit_workflow.md
+++ b/conductor/edit_workflow.md
@@ -38,6 +38,33 @@ Before ANY edit to a function you haven't touched recently:
 - Nested blocks: `   ` (3 spaces total)
 - NO 4-space indentation anywhere in this file
 
+### 6. The Decorator-Orphan Pitfall (Added 2026-06-07)
+
+When inserting new methods **before an existing `@property` def**:
+```
+@property
+def perf_profiling_enabled(self) -> bool:
+    ...
+```
+If you anchor on `def perf_profiling_enabled` and insert before it, the `@property` decorator on the line above is left orphaned on the line right before YOUR new method. Now `@property` decorates your method (which is no longer a property), and the original setter `@perf_profiling_enabled.setter` blows up at import with `'function' object has no attribute 'setter'`.
+
+**Fix:** Anchor on a non-decorated landmark, or include the decorator in the replacement:
+- `old_string` = `  self._init_actions()\n\n @property\n def perf_profiling_enabled`
+- `new_string` = `  self._init_actions()\n\n def your_new(...)\n ...\n\n @property\n def perf_profiling_enabled`
+
+This keeps the `@property` attached to its original method.
+
+### 7. ast.parse() Is Not Enough (Added 2026-06-07)
+
+`py_check_syntax` only confirms `ast.parse()` succeeds. Semantic errors (wrong decorator targets, wrong base class, wrong attribute, missing `self`) are NOT caught. After any multi-line edit, ALWAYS:
+1. Import the module: `python -c "from src.app_controller import AppController"`
+2. Instantiate the class
+3. Call the new method in the way it's expected to be called (`ctrl.foo_ts` for a property, `ctrl.foo_ts()` for a method)
+
+### 8. Do Not Use `set_file_slice` For Multi-Line Content (Added 2026-06-07)
+
+`set_file_slice` does literal line replacement by design. It does not reindent, does not normalize EOL, does not parse decorators. Use it for surgical line-level edits (3-10 lines). If you need to insert or replace a multi-method block, use `manual-slop_edit_file` with verified exact-text old_string/new_string, or use `py_add_def` / `py_update_definition` for class/method-level work.
+
 ## Step-by-Step Workflow for gui_2.py
 
 ### Before ANY edit: