M4: subagent context-file reporting to the job board

Lets subagents report context files back to the job board (surfaced from the read tool) so the parent session's next-turn context includes what a background child has been looking at.

crates/harness-tools/src/bash.rs

@@ -150,6 +150,7 @@ mod tests {
             ),
             metadata,
             spawner: None,
+            context_reporter: None,
         }
     }
 

crates/harness-tools/src/edit/mod.rs

@@ -233,6 +233,7 @@ mod tests {
             ),
             metadata,
             spawner: None,
+            context_reporter: None,
         }
     }
 

crates/harness-tools/src/glob.rs

@@ -131,6 +131,7 @@ mod tests {
             ),
             metadata,
             spawner: None,
+            context_reporter: None,
         }
     }
 

crates/harness-tools/src/grep.rs

@@ -160,6 +160,7 @@ mod tests {
             ),
             metadata,
             spawner: None,
+            context_reporter: None,
         }
     }
 

crates/harness-tools/src/read.rs

@@ -102,6 +102,13 @@ impl Tool for ReadTool {
                 "(empty file or offset past end)".to_string(),
             ));
         }
+
+        // In a subagent session, advertise this read on the job board.
+        if let Some(reporter) = &ctx.context_reporter {
+            let reported = paths::relative_pattern(&ctx.cwd, &path);
+            reporter.report_file(reported, numbered.len() as u32).await;
+        }
+
         Ok(ToolOutput::new(
             params.file_path.clone(),
             numbered.join("\n"),
@@ -140,6 +147,7 @@ mod tests {
             ),
             metadata,
             spawner: None,
+            context_reporter: None,
         }
     }
 

crates/harness-tools/src/write.rs

@@ -115,6 +115,7 @@ mod tests {
             ),
             metadata,
             spawner: None,
+            context_reporter: None,
         }
     }