Add Windows cross-platform support

.project/PROMPT.md

@@ -16,7 +16,7 @@ If HANDOFF.md doesn't exist, this is the first iteration. Read `.project/SPEC.md
 ### 2. Pick a Task
 
 ```bash
-.project/task next
+python .project/task next
 ```
 
 This returns the highest-priority task with satisfied dependencies. If it returns an in-progress task, a previous iteration crashed — pick up where it left off.
@@ -30,15 +30,15 @@ echo "DONE: All tasks complete" > .project/STOP
 ### 3. Read the Task
 
 ```bash
-.project/task <ID>
+python .project/task <ID>
 ```
 
 Read the full task file. Understand the acceptance criteria before writing any code.
 
 ### 4. Implement
 
 ```bash
-.project/task <ID> progress
+python .project/task <ID> progress
 ```
 
 Mark it in-progress, then implement. Follow existing code patterns. Make the smallest change that satisfies the acceptance criteria.
@@ -55,7 +55,7 @@ Run the project's quality checks (lint, typecheck, test — whatever applies). D
 ### 6. Complete
 
 ```bash
-.project/task <ID> done
+python .project/task <ID> done
 ```
 
 Commit your changes:
@@ -83,13 +83,13 @@ git add -A && git commit -m "feat(<scope>): <ID> - <description>"
 <anything the next iteration needs to know>
 
 ## Remaining Work
-<output of .project/task list>
+<output of python .project/task list>
 ```
 
 ### 8. Check for Completion
 
 ```bash
-.project/task list
+python .project/task list
 ```
 
 If all tasks are done (nothing under OPEN or IN PROGRESS), write a STOP file:
@@ -117,3 +117,4 @@ echo "CLARIFY: <question for the human>" > .project/STOP
 - **Always write HANDOFF.md last.** It's the next iteration's memory.
 - **Don't be clever.** Simple, obvious code that works.
 - **Commit after completing each task.** Never leave uncommitted work.
+- **Use the Python venv.** If a `.venv` directory does not yet exist, create one with `python -m venv .venv` and activate it with `source .venv/Scripts/activate` (Windows) or `source .venv/bin/activate` (Linux/macOS) before installing packages or running Python commands. Always activate the venv before running pip, pytest, ruff, or any project Python code. Check for the venv at the start of every iteration.

.project/loop

@@ -30,7 +30,7 @@ LOGS_DIR = os.path.join(SCRIPT_DIR, "logs")
 
 
 def read_file(path):
-    with open(path, "r") as f:
+    with open(path, "r", encoding="utf-8") as f:
         return f.read()
 
 
@@ -42,7 +42,7 @@ def clean_stale_stop():
 
 def ensure_learnings():
     if not os.path.exists(LEARNINGS_FILE):
-        with open(LEARNINGS_FILE, "w") as f:
+        with open(LEARNINGS_FILE, "w", encoding="utf-8") as f:
             f.write("# Learnings\n\nPatterns and gotchas discovered during implementation.\n")
 
 
@@ -178,7 +178,7 @@ def run_iteration(iteration, model=None, verbose=False):
             cwd=PROJECT_DIR,
         )
 
-        with open(jsonl_path, "w") as jsonl_file:
+        with open(jsonl_path, "w", encoding="utf-8") as jsonl_file:
             for raw_line in proc.stdout:
                 line = raw_line.decode("utf-8", errors="replace")
                 # Write raw JSON to log
@@ -244,7 +244,7 @@ def run_iteration(iteration, model=None, verbose=False):
 
 def _write_summary(path, header, model, tools, texts, result, elapsed, error=None):
     """Write a human-readable iteration summary."""
-    with open(path, "w") as f:
+    with open(path, "w", encoding="utf-8") as f:
         f.write(f"# {header}\n\n")
         f.write(f"- **Model**: {model}\n")
         f.write(f"- **Duration**: {elapsed:.0f}s\n")
@@ -300,7 +300,7 @@ def main():
             # Re-read result from jsonl for accurate cost
             jsonl_path = log_path.replace(".md", ".jsonl")
             if os.path.exists(jsonl_path):
-                with open(jsonl_path) as f:
+                with open(jsonl_path, encoding="utf-8") as f:
                     for line in f:
                         try:
                             obj = json.loads(line)