feat: real-time tool call streaming indicator with blinking UI

- Add ToolParsingHint enum (Detected/Active/Complete) for UI feedback
- New UiWriter methods: print_tool_streaming_hint(), print_tool_streaming_active()
- Refactor ConsoleUiWriter state to use atomics in ParsingHintState
- Add tool_call_streaming field to CompletionChunk for provider hints
- Anthropic provider sends streaming hints when tool name detected
- New streaming helpers: make_tool_streaming_hint(), make_tool_streaming_active()

Parser improvements:
- Add is_json_invalidated() to detect false positive tool patterns
- Fix tool result poisoning when file contents contain partial JSON
- Unescaped newlines in strings or prose after JSON invalidates detection

User sees ' ● tool_name |' immediately when tool call starts streaming,
with blinking indicator while args are received.

crates/g3-core/src/lib.rs

@@ -1959,6 +1959,17 @@ Skip if nothing new. Be brief."#;
                             );
                         }
 
+                        // Handle tool call streaming hint (show UI indicator immediately)
+                        if let Some(ref tool_name) = chunk.tool_call_streaming {
+                            if tool_name.is_empty() {
+                                // Empty string = "active" hint for blinking
+                                self.ui_writer.print_tool_streaming_active();
+                            } else {
+                                // Non-empty = "detected" hint with tool name
+                                self.ui_writer.print_tool_streaming_hint(tool_name);
+                            }
+                        }
+
                         // Store raw chunk for debugging (limit to first 20 and last 5)
                         if chunks_received < 20 || chunk.finished {
                             raw_chunks.push(format!(