From f705497b80ba86a8d63ee1cba6b026a1c5d98cec Mon Sep 17 00:00:00 2001
From: Tommy Carpenter <9419125+tommyjcarpenter@users.noreply.github.com>
Date: Fri, 26 Jun 2026 06:37:33 -0400
Subject: [PATCH] Refresh Explorer association cache after registering file
 associations

`install_file_associations` wrote each per-user class registration but never told
Explorer to refresh its cached file-type defaults, so a newly registered association only
took effect after the next sign-in or an Explorer restart. For an extension Explorer had
already resolved to another app (e.g. `.json` -> Visual Studio) the stale default kept
winning on double-click even though the new type showed up in "Open with". Extensions
nothing else had claimed (`.md`, `.yaml`, `.toml`) had no cached default, so they resolved
fresh to the new handler and masked the gap.

Changes:
- Add `_notify_assoc_changed()`, which calls `SHChangeNotify(SHCNE_ASSOCCHANGED, SHCNF_IDLIST, ...)` via `ctypes` to invalidate Explorer's association cache. It uses a local `import ctypes` to match the module's existing pattern for Windows-only APIs (`winreg`), so the module still imports cleanly on the Linux CI runner.
- Call it once in `install_file_associations` after the registration loop, so the broadcast fires a single time regardless of how many extensions were registered.

No unit test added: the helper is a thin `shell32` call with no return value to assert on; the existing import smoke test already covers it loading.
---
 bootstrap/os_specific/windows.py | 26 +++++++++++++++++++++++++-
 1 file changed, 25 insertions(+), 1 deletion(-)

diff --git a/bootstrap/os_specific/windows.py b/bootstrap/os_specific/windows.py
index 94dd314..96f3af5 100644
--- a/bootstrap/os_specific/windows.py
+++ b/bootstrap/os_specific/windows.py
@@ -146,8 +146,30 @@ def set_file_assoc(ext, progid, cmd, name=None, icon=None, label=None):
             pass
 
 
+def _notify_assoc_changed():
+    """Broadcast SHCNE_ASSOCCHANGED so Explorer drops its cached file-type defaults.
+
+    Writing HKCU\\Software\\Classes alone isn't enough: Explorer caches the resolved
+    default per extension, so a freshly written association doesn't take effect until the
+    next sign-in or an Explorer restart. For an extension Explorer already resolved to a
+    different app (e.g. .json -> Visual Studio) the stale default keeps winning until the
+    cache is invalidated — which is why a newly registered type appears in "Open with" yet
+    double-click still opens the old app. SHChangeNotify is the documented, admin-free way
+    to invalidate that cache; it lives in shell32 and returns nothing.
+    """
+    import ctypes
+
+    SHCNE_ASSOCCHANGED = 0x08000000
+    SHCNF_IDLIST = 0x0000
+    ctypes.windll.shell32.SHChangeNotify(SHCNE_ASSOCCHANGED, SHCNF_IDLIST, None, None)
+
+
 def install_file_associations(config):
-    """Top-level entry: reads config['file_associations']['windows'] and registers each."""
+    """Top-level entry: reads config['file_associations']['windows'] and registers each.
+
+    After registering every entry, broadcasts a single SHCNE_ASSOCCHANGED so Explorer
+    picks up the new defaults immediately instead of on the next sign-in.
+    """
     if "file_associations" not in config:
         log.skip("No file_associations in config")
         return
@@ -168,3 +190,5 @@ def install_file_associations(config):
             icon=assoc.get("icon"),
             label=assoc.get("label"),
         )
+    log.action("refreshing Explorer association cache (SHCNE_ASSOCCHANGED)")
+    _notify_assoc_changed()