Fix Windows Unicode crash and Bedrock Claude 4.6 model IDs

Windows (fixes #65):
- Reconfigure stdout/stderr to UTF-8 on Windows in wrap.py (cp1252 can't
encode box-drawing characters in CLI banner)
- Pass PYTHONIOENCODING=utf-8 to proxy subprocess env
- Add encoding="utf-8", errors="replace" to subprocess.run() calls in
rtk/installer.py

Bedrock (fixes #64):
- Fix Claude 4.6 model IDs in static fallback map:
anthropic.claude-opus-4-6-v1:0 → anthropic.claude-opus-4-6-v1
anthropic.claude-sonnet-4-6-v1:0 → anthropic.claude-sonnet-4-6

headroom/backends/litellm.py

@@ -96,8 +96,8 @@ def _build_bedrock_fallback_map(region: str) -> dict[str, str]:
     # Base model IDs without region prefix
     _CLAUDE_MODELS = [
         # Claude 4.6
-        ("claude-opus-4-6", "anthropic.claude-opus-4-6-v1:0"),
-        ("claude-sonnet-4-6", "anthropic.claude-sonnet-4-6-v1:0"),
+        ("claude-opus-4-6", "anthropic.claude-opus-4-6-v1"),
+        ("claude-sonnet-4-6", "anthropic.claude-sonnet-4-6"),
         # Claude 4.5
         ("claude-sonnet-4-5-20250929", "anthropic.claude-sonnet-4-5-20250929-v1:0"),
         ("claude-opus-4-5-20251101", "anthropic.claude-opus-4-5-20251101-v1:0"),

headroom/cli/wrap.py

@@ -12,6 +12,7 @@ Usage:
 
 from __future__ import annotations
 
+import io
 import os
 import shutil
 import signal
@@ -22,6 +23,12 @@ import time
 from pathlib import Path
 from typing import Any
 
+# Fix Windows cp1252 encoding — box-drawing characters require UTF-8
+if sys.platform == "win32" and hasattr(sys.stdout, "buffer"):
+    if sys.stdout.encoding and sys.stdout.encoding.lower().replace("-", "") != "utf8":
+        sys.stdout = io.TextIOWrapper(sys.stdout.buffer, encoding="utf-8", errors="replace")
+        sys.stderr = io.TextIOWrapper(sys.stderr.buffer, encoding="utf-8", errors="replace")
+
 import click
 
 from .main import main
@@ -68,10 +75,15 @@ def _start_proxy(port: int, *, learn: bool = False) -> subprocess.Popen:
     log_path = _get_log_path()
     log_file = open(log_path, "a")  # noqa: SIM115
 
+    # Ensure proxy subprocess uses UTF-8 (Windows defaults to cp1252)
+    proxy_env = os.environ.copy()
+    proxy_env["PYTHONIOENCODING"] = "utf-8"
+
     proc = subprocess.Popen(
         cmd,
         stdout=log_file,
         stderr=log_file,
+        env=proxy_env,
     )
 
     # Wait for proxy to be ready (up to 15 seconds)

headroom/rtk/installer.py

@@ -125,6 +125,8 @@ def download_rtk(version: str | None = None) -> Path:
             [str(RTK_BIN_PATH), "--version"],
             capture_output=True,
             text=True,
+            encoding="utf-8",
+            errors="replace",
             timeout=5,
         )
         if result.returncode != 0:
@@ -153,6 +155,8 @@ def register_claude_hooks(rtk_path: Path | None = None) -> bool:
             [str(rtk_path), "init", "--global", "--auto-patch"],
             capture_output=True,
             text=True,
+            encoding="utf-8",
+            errors="replace",
             timeout=10,
         )
         if result.returncode == 0: