harness-tui + engine: jobs pane, subtask drill-in, reminders (M4)

TUI: Ctrl+J (or /jobs) opens a jobs pane listing the current session's board —
alias, agent, state, objective, files read — populated on load and kept live via
JobUpdated events; Enter drills into a subtask's child session. Snapshot test added.

Engine: optional orchestration reminders (off by default) injected as synthetic,
non-persisted turn-start blocks and, after a file tool runs, an after-file-tool
block on the following turn. Processor reports file-tool usage via StepOutcome.

This completes M4.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

crates/harness-core/src/engine/processor.rs

@@ -33,6 +33,9 @@ pub struct StepOutcome {
     /// Dollar cost of this step's usage (0.0 when no pricing is available).
     pub cost: f64,
     pub aborted: bool,
+    /// Whether a file-mutating tool (`edit`/`write`) ran this step — drives the optional
+    /// `after_file_tool` reminder injection on the next turn.
+    pub used_file_tool: bool,
 }
 
 pub struct StepError {
@@ -98,9 +101,13 @@ impl FlushTracker {
     }
 }
 
+/// Tool names that mutate files — after one runs, the optional `after_file_tool` reminder fires.
+const FILE_TOOLS: &[&str] = &["edit", "write"];
+
 struct Run<'a> {
     ctx: &'a StepContext,
     assistant: Option<Message>,
+    used_file_tool: bool,
     next_idx: u32,
     active_text: Option<PartId>,
     active_reasoning: Option<PartId>,
@@ -117,6 +124,7 @@ impl<'a> Run<'a> {
         Self {
             ctx,
             assistant: None,
+            used_file_tool: false,
             next_idx: 0,
             active_text: None,
             active_reasoning: None,
@@ -386,6 +394,9 @@ impl<'a> Run<'a> {
         input: serde_json::Value,
         doomloop: &mut DoomLoopGuard,
     ) -> Result<(), ProviderError> {
+        if FILE_TOOLS.contains(&name.as_str()) {
+            self.used_file_tool = true;
+        }
         let part_id = self.pending_tools.remove(&call_id).unwrap_or_default();
         let running = Part {
             id: part_id.clone(),
@@ -607,6 +618,7 @@ pub async fn process_step(
                     usage,
                     cost: step_cost,
                     aborted: true,
+                    used_file_tool: run.used_file_tool,
                 });
             }
         };
@@ -679,5 +691,6 @@ pub async fn process_step(
         usage,
         cost: step_cost,
         aborted: false,
+        used_file_tool: run.used_file_tool,
     })
 }