feat(acp): forward meta/locations fields and use parentToolUseId for precise Agent child grouping

Forward the previously-dropped `locations` and `meta` fields from ACP
SDK ToolCall/ToolCallUpdate events through to the frontend. The meta
field carries `claudeCode.parentToolUseId` which enables precise
parent-child matching for concurrent Agent tool calls during streaming.

- Forward locations/meta in Rust AcpEvent types and connection handlers
- Use parentToolUseId for exact agent→child mapping, with position-based
  fallback for agents that don't provide it (Codex, OpenCode)
- Replace `any` types with proper ToolCallMeta / unknown types
- Add runtime guards for meta field parsing (defensive against
  unexpected shapes from different agents)
- Cache inferLiveToolName results per tool_call_id to avoid redundant
  computation across Phase 1 and Phase 2
- Lazy-construct agentStats only when children exist

src-tauri/src/acp/connection.rs

@@ -1554,6 +1554,8 @@ fn emit_terminal_output_update(
             raw_input: None,
             raw_output: Some(output),
             raw_output_append: Some(append),
+            locations: None,
+            meta: None,
         },
     );
 }
@@ -2501,6 +2503,12 @@ fn emit_conversation_update(
                 .map(|text| resolve_live_tool_input(&text, cwd));
             let raw_output = json_value_to_text(&tc.raw_output)
                 .map(|text| structurize_live_output(&text));
+            let locations = if tc.locations.is_empty() {
+                None
+            } else {
+                serde_json::to_value(&tc.locations).ok()
+            };
+            let meta = tc.meta.map(serde_json::Value::Object);
             crate::web::event_bridge::emit_event(
                 emitter,
                 "acp://event",
@@ -2513,6 +2521,8 @@ fn emit_conversation_update(
                     content,
                     raw_input,
                     raw_output,
+                    locations,
+                    meta,
                 },
             );
         }
@@ -2526,6 +2536,13 @@ fn emit_conversation_update(
                 .map(|text| resolve_live_tool_input(&text, cwd));
             let raw_output = json_value_to_text(&tcu.fields.raw_output)
                 .map(|text| structurize_live_output(&text));
+            let locations = tcu
+                .fields
+                .locations
+                .as_ref()
+                .filter(|l| !l.is_empty())
+                .and_then(|l| serde_json::to_value(l).ok());
+            let meta = tcu.meta.clone().map(serde_json::Value::Object);
             crate::web::event_bridge::emit_event(
                 emitter,
                 "acp://event",
@@ -2538,6 +2555,8 @@ fn emit_conversation_update(
                     raw_input,
                     raw_output,
                     raw_output_append: None,
+                    locations,
+                    meta,
                 },
             );
         }

src-tauri/src/acp/types.rs

@@ -63,6 +63,10 @@ pub enum AcpEvent {
         content: Option<String>,
         raw_input: Option<String>,
         raw_output: Option<String>,
+        #[serde(skip_serializing_if = "Option::is_none")]
+        locations: Option<serde_json::Value>,
+        #[serde(skip_serializing_if = "Option::is_none")]
+        meta: Option<serde_json::Value>,
     },
     /// Tool call status/content updated
     ToolCallUpdate {
@@ -75,6 +79,10 @@ pub enum AcpEvent {
         raw_output: Option<String>,
         #[serde(skip_serializing_if = "Option::is_none")]
         raw_output_append: Option<bool>,
+        #[serde(skip_serializing_if = "Option::is_none")]
+        locations: Option<serde_json::Value>,
+        #[serde(skip_serializing_if = "Option::is_none")]
+        meta: Option<serde_json::Value>,
     },
     /// Agent requests permission
     PermissionRequest {