claudetool: add simplified patch support

For weaker models.

Also, improve fallback parsing introduced earlier.
diff --git a/llm/ant/ant.go b/llm/ant/ant.go
index 046456f..7be2911 100644
--- a/llm/ant/ant.go
+++ b/llm/ant/ant.go
@@ -565,3 +565,8 @@
 		}
 	}
 }
+
+// For debugging only, Claude can definitely handle the full patch tool.
+// func (s *Service) UseSimplifiedPatch() bool {
+// 	return true
+// }
diff --git a/llm/llm.go b/llm/llm.go
index ffaad3e..19a1d8d 100644
--- a/llm/llm.go
+++ b/llm/llm.go
@@ -21,6 +21,18 @@
 	TokenContextWindow() int
 }
 
+type SimplifiedPatcher interface {
+	// UseSimplifiedPatch reports whether the service should use the simplified patch input schema.
+	UseSimplifiedPatch() bool
+}
+
+func UseSimplifiedPatch(svc Service) bool {
+	if sp, ok := svc.(SimplifiedPatcher); ok {
+		return sp.UseSimplifiedPatch()
+	}
+	return false
+}
+
 // MustSchema validates that schema is a valid JSON schema and returns it as a json.RawMessage.
 // It panics if the schema is invalid.
 // The schema must have at least type="object" and a properties key.
diff --git a/llm/oai/oai.go b/llm/oai/oai.go
index c561095..6a32a74 100644
--- a/llm/oai/oai.go
+++ b/llm/oai/oai.go
@@ -37,11 +37,12 @@
 )
 
 type Model struct {
-	UserName         string // provided by the user to identify this model (e.g. "gpt4.1")
-	ModelName        string // provided to the service provide to specify which model to use (e.g. "gpt-4.1-2025-04-14")
-	URL              string
-	APIKeyEnv        string // environment variable name for the API key
-	IsReasoningModel bool   // whether this model is a reasoning model (e.g. O3, O4-mini)
+	UserName           string // provided by the user to identify this model (e.g. "gpt4.1")
+	ModelName          string // provided to the service provide to specify which model to use (e.g. "gpt-4.1-2025-04-14")
+	URL                string
+	APIKeyEnv          string // environment variable name for the API key
+	IsReasoningModel   bool   // whether this model is a reasoning model (e.g. O3, O4-mini)
+	UseSimplifiedPatch bool   // whether to use the simplified patch input schema; defaults to false
 }
 
 var (
@@ -210,17 +211,19 @@
 	}
 
 	Qwen3CoderFireworks = Model{
-		UserName:  "qwen3-coder-fireworks",
-		ModelName: "accounts/fireworks/models/qwen3-coder-480b-a35b-instruct",
-		URL:       FireworksURL,
-		APIKeyEnv: FireworksAPIKeyEnv,
+		UserName:           "qwen3-coder-fireworks",
+		ModelName:          "accounts/fireworks/models/qwen3-coder-480b-a35b-instruct",
+		URL:                FireworksURL,
+		APIKeyEnv:          FireworksAPIKeyEnv,
+		UseSimplifiedPatch: true,
 	}
 
 	// Qwen is a skaband-specific model name for Qwen3-Coder
 	// Provider details (URL and APIKeyEnv) are handled by skaband
 	Qwen = Model{
-		UserName:  "qwen",
-		ModelName: "qwen", // skaband will map this to the actual provider model
+		UserName:           "qwen",
+		ModelName:          "qwen", // skaband will map this to the actual provider model
+		UseSimplifiedPatch: true,
 	}
 )
 
@@ -783,3 +786,7 @@
 		}
 	}
 }
+
+func (s *Service) UseSimplifiedPatch() bool {
+	return s.Model.UseSimplifiedPatch
+}