fix: decode tag names from the URL only once

The tag lookup, rename and delete routes ran urllib.parse.unquote on
match_info values that aiohttp had already percent-decoded, so a tag
literally named '%41' (requested as %2541) was handled as 'A'. The
second decode is dropped.

py/api/prompts.py

@@ -387,9 +387,9 @@ class PromptRoutesMixin:
     async def get_tag_prompts(self, request):
         """Get prompts for a single tag."""
         try:
-            from urllib.parse import unquote
-
-            tag_name = unquote(request.match_info.get("tag_name", ""))
+            # aiohttp has already percent-decoded match_info; decoding again
+            # would turn a tag literally named "%41" into "A".
+            tag_name = request.match_info.get("tag_name", "")
             if not tag_name:
                 return web.json_response(
                     {"success": False, "error": "Tag name required"}, status=400
@@ -497,9 +497,9 @@ class PromptRoutesMixin:
     async def rename_tag_endpoint(self, request):
         """Rename a tag across all prompts."""
         try:
-            from urllib.parse import unquote
-
-            tag_name = unquote(request.match_info.get("tag_name", ""))
+            # aiohttp has already percent-decoded match_info; decoding again
+            # would turn a tag literally named "%41" into "A".
+            tag_name = request.match_info.get("tag_name", "")
             if not tag_name:
                 return web.json_response(
                     {"success": False, "error": "Tag name required"}, status=400
@@ -542,9 +542,9 @@ class PromptRoutesMixin:
     async def delete_tag_endpoint(self, request):
         """Delete a tag from all prompts."""
         try:
-            from urllib.parse import unquote
-
-            tag_name = unquote(request.match_info.get("tag_name", ""))
+            # aiohttp has already percent-decoded match_info; decoding again
+            # would turn a tag literally named "%41" into "A".
+            tag_name = request.match_info.get("tag_name", "")
             if not tag_name:
                 return web.json_response(
                     {"success": False, "error": "Tag name required"}, status=400

tests/test_api_prompts.py

@@ -431,6 +431,39 @@ class TestPublicPathsInPromptResponses(RouteCoverageCase):
             self.assertIn("prompts.db", data["error"], route)
 
 
+class TestTagNamesAreDecodedOnce(RouteCoverageCase):
+    """aiohttp already decodes match_info; a tag literally named '%41' stays '%41'."""
+
+    async def setUpAsync(self):
+        await super().setUpAsync()
+        self.pid = self._save_prompt("percent tag", tags=["%41"])
+
+    async def test_tag_prompts_lookup(self):
+        status, data = await self._json("GET", "/prompt_manager/tags/%2541/prompts")
+
+        self.assertEqual(status, 200)
+        self.assertEqual(data["tag"], "%41")
+        self.assertEqual(len(data["prompts"]), 1)
+
+    async def test_rename_tag(self):
+        status, data = await self._json(
+            "PUT", "/prompt_manager/tags/%2541", json={"new_name": "renamed"}
+        )
+
+        self.assertEqual(status, 200)
+        self.assertEqual(data["old_name"], "%41")
+        self.assertEqual(data["affected_count"], 1)
+        self.assertEqual(self.api.db.get_prompt_by_id(self.pid)["tags"], ["renamed"])
+
+    async def test_delete_tag(self):
+        status, data = await self._json("DELETE", "/prompt_manager/tags/%2541")
+
+        self.assertEqual(status, 200)
+        self.assertEqual(data["tag_name"], "%41")
+        self.assertEqual(data["affected_count"], 1)
+        self.assertEqual(self.api.db.get_prompt_by_id(self.pid)["tags"], [])
+
+
 class TestTagMutationRoutes(RouteCoverageCase):
 
     async def test_rename_rejects_bad_json_and_empty_name(self):