feat: add 50% step budget warning before exhaustion

Nudge the agent at 50% of step budget to encourage taking action
rather than looping on research. The warning explains that action
tools (file_write, file_edit, shell) reset the counter.

agent/loop.go

@@ -667,17 +667,24 @@ func run(ctx context.Context, cfg agentConfig, state state) error {
 			}
 		}
 
-		// Soft step-budget guardrail: when MaxSteps is set and the budget is
-		// exhausted, nudge the model to wrap up and exit cleanly. This is not
-		// a hard abort — the model gets one final turn without tools to emit
-		// a summary or hand-off message.
-		if cfg.MaxSteps > 0 && step >= cfg.MaxSteps-1 {
-			emit(cfg, Event{Role: "maxsteps", Content: fmt.Sprintf("%d", step+1)})
-			state.update(backend.Message{
-				Role:    "user",
-				Content: fmt.Sprintf("[system: step budget exhausted (%d/%d steps used). Stop calling toolsrv. Summarize what you have done and what remains, then stop.]", step+1, cfg.MaxSteps),
-			}, nil)
-			break
+		// Step budget warnings: nudge the agent at 50% and when exhausted.
+		// These only fire for research-heavy loops — action tools (file_write,
+		// file_edit, shell) reset the counter, so active progress never triggers.
+		if cfg.MaxSteps > 0 {
+			halfBudget := cfg.MaxSteps / 2
+			if step == halfBudget {
+				state.update(backend.Message{
+					Role:    "user",
+					Content: fmt.Sprintf("[system: you have used %d/%d research steps without taking action. Consider making progress — write code, edit files, or run commands. Action tools reset this counter.]", step, cfg.MaxSteps),
+				}, nil)
+			} else if step >= cfg.MaxSteps-1 {
+				emit(cfg, Event{Role: "maxsteps", Content: fmt.Sprintf("%d", step+1)})
+				state.update(backend.Message{
+					Role:    "user",
+					Content: fmt.Sprintf("[system: step budget exhausted (%d/%d steps used). Stop calling tools. Summarize what you have done and what remains, then stop.]", step+1, cfg.MaxSteps),
+				}, nil)
+				break
+			}
 		}
 
 		// Periodic task state re-injection: every N tool rounds, surface the