Add idle-state classifier and Solo-parity timer tools

Classifies every running child as idle/working/thinking/permission/error
using one of three pluggable strategies (output_activity,
osc_title_stability, osc_title_status) plus optional regex promoters
applied to the tail of recent output. State and last-match reason are
exposed via MCP on ProcessInfo and get_process_status. Per-preset
configuration lives on a new preset.IdleDetection block with bundled
defaults for the first-party claude/codex/opencode presets.

OSC title plumbing is exposed as Emulator.Title(), polled from the
session pump after each emulator write so title-change activity feeds
into the classifier without an extra cgo callback.

The MCP timer surface expands to match Solo: timer_set,
timer_fire_when_idle_any/all, timer_cancel, timer_pause, timer_resume,
timer_list. timer_wait is now a thin wrapper that shares the same
manager so it shows up in timer_list while pending. Timer bodies are
delivered to the owner process through the existing
InjectAsOrchestrator path. Top-level (non-agent) callers can attach
timers to a specific process via owner_process_id; omitting it grants
universal cancel/pause/resume/list privileges.

The sidebar gains a state glyph per process row and appends a
nearest-timer indicator when one is pending or paused.

Tests: idle_test.go covers the classify() pure function across the
three strategies and regex promotion; timers_test.go covers the
manager. Harness scenarios cover output_activity, osc_title_stability,
osc_title_status, and regex promotion, plus timer_set delivery,
cancel, pause/resume, idle_any-on-transition, idle_all-pending, and
idle_all-already-satisfied. A new wait_until_mcp harness step type
polls an MCP method until an assertion holds.

internal/app/sidebar.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"os"
 	"strings"
+	"time"
 )
 
 const (
@@ -11,6 +12,24 @@ const (
 	statusRows  = 1
 )
 
+// formatShortDuration renders a duration as a short, sidebar-friendly
+// suffix: ms under 1s, "12s" under 60s, "3m" otherwise.
+func formatShortDuration(d time.Duration) string {
+	if d <= 0 {
+		return "0s"
+	}
+	if d < time.Second {
+		return fmt.Sprintf("%dms", int(d/time.Millisecond))
+	}
+	if d < time.Minute {
+		return fmt.Sprintf("%ds", int(d/time.Second))
+	}
+	if d < time.Hour {
+		return fmt.Sprintf("%dm", int(d/time.Minute))
+	}
+	return fmt.Sprintf("%dh", int(d/time.Hour))
+}
+
 // drawSidebar paints the right-rail session tree + scratchpad list.
 // SPEC §4: the rail is the active session's child hierarchy on top and
 // the scratchpad list (with preview) on the bottom.
@@ -62,14 +81,56 @@ func (st *uiState) drawSidebar() {
 		write(" " + styleActive + text + styleReset)
 		write(" " + styleBorder + strings.Repeat("─", width-2) + styleReset)
 	}
+	// timerIndicator returns a short " ⏱ 12s" or " ⏸ paused" suffix
+	// when c has a pending or paused timer attached (owns or watches).
+	// Empty string when no timer is in play.
+	timerIndicator := func(c *Child) string {
+		if st.timers == nil {
+			return ""
+		}
+		info := st.timers.activeForChild(c.ID)
+		if info == nil {
+			return ""
+		}
+		if info.Status == timerStatusPaused {
+			return " " + styleDim + "⏸" + styleReset
+		}
+		remaining := ""
+		if info.FiresAtUnixMS > 0 {
+			d := time.Until(time.UnixMilli(info.FiresAtUnixMS))
+			if d < 0 {
+				d = 0
+			}
+			remaining = formatShortDuration(d)
+		}
+		return " " + styleDim + "⏱" + styleReset + " " + styleHint + remaining + styleReset
+	}
 	statusGlyph := func(c *Child, focused bool) string {
 		if c.Status() != StatusRunning {
 			return styleDim + "○" + styleReset
 		}
+		// Idle-detection states paint over the plain running glyph so
+		// the rail communicates "running but waiting on you" vs "running
+		// and busy" at a glance. Focused entries always use the accent
+		// colour so the user's selection stays visible.
+		style := styleHint
 		if focused {
-			return styleAccent + "●" + styleReset
+			style = styleAccent
+		}
+		switch c.IdleState() {
+		case StateError:
+			return styleError + "✕" + styleReset
+		case StatePermission:
+			return styleAccent + "?" + styleReset
+		case StateThinking:
+			return style + "◐" + styleReset
+		case StateIdle:
+			return style + "○" + styleReset
+		case StateWorking:
+			return style + "●" + styleReset
+		default:
+			return style + "●" + styleReset
 		}
-		return styleHint + "●" + styleReset
 	}
 
 	// Processes section — top-level command/terminal processes,
@@ -92,9 +153,9 @@ func (st *uiState) drawSidebar() {
 		var line string
 		if focused {
 			line = " " + styleAccent + "▎" + styleReset + " " + glyph + " " +
-				styleBold + c.DisplayName() + styleReset + marker
+				styleBold + c.DisplayName() + styleReset + marker + timerIndicator(c)
 		} else {
-			line = "   " + glyph + " " + styleHint + c.DisplayName() + styleReset + marker
+			line = "   " + glyph + " " + styleHint + c.DisplayName() + styleReset + marker + timerIndicator(c)
 		}
 		write(line)
 	}
@@ -124,9 +185,9 @@ func (st *uiState) drawSidebar() {
 		var line string
 		if focused {
 			line = " " + styleAccent + "▎" + styleReset + " " + indent + glyph + " " +
-				styleBold + c.DisplayName() + styleReset
+				styleBold + c.DisplayName() + styleReset + timerIndicator(c)
 		} else {
-			line = "   " + indent + glyph + " " + styleHint + c.DisplayName() + styleReset
+			line = "   " + indent + glyph + " " + styleHint + c.DisplayName() + styleReset + timerIndicator(c)
 		}
 		write(line)
 	}