refactor(prime): split 1833-line file into logical modules

Extract prime.go into focused files:
- prime_session.go: session ID handling, hooks, persistence
- prime_output.go: all output/rendering functions
- prime_molecule.go: molecule workflow context
- prime_state.go: handoff markers, session state detection

Main prime.go now ~730 lines with core flow visible as "table of contents".
No behavior changes - pure file organization following Go idioms.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/cmd/prime_state.go

@@ -0,0 +1,116 @@
+package cmd
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+	"time"
+
+	"github.com/steveyegge/gastown/internal/beads"
+	"github.com/steveyegge/gastown/internal/checkpoint"
+	"github.com/steveyegge/gastown/internal/constants"
+)
+
+// SessionState represents the detected session state for observability.
+type SessionState struct {
+	State         string `json:"state"`                    // normal, post-handoff, crash-recovery, autonomous
+	Role          Role   `json:"role"`                     // detected role
+	PrevSession   string `json:"prev_session,omitempty"`   // for post-handoff
+	CheckpointAge string `json:"checkpoint_age,omitempty"` // for crash-recovery
+	HookedBead    string `json:"hooked_bead,omitempty"`    // for autonomous
+}
+
+// detectSessionState returns the current session state without side effects.
+func detectSessionState(ctx RoleContext) SessionState {
+	state := SessionState{
+		State: "normal",
+		Role:  ctx.Role,
+	}
+
+	// Check for handoff marker (post-handoff state)
+	markerPath := filepath.Join(ctx.WorkDir, constants.DirRuntime, constants.FileHandoffMarker)
+	if data, err := os.ReadFile(markerPath); err == nil {
+		state.State = "post-handoff"
+		state.PrevSession = strings.TrimSpace(string(data))
+		return state
+	}
+
+	// Check for checkpoint (crash-recovery state) - only for polecat/crew
+	if ctx.Role == RolePolecat || ctx.Role == RoleCrew {
+		if cp, err := checkpoint.Read(ctx.WorkDir); err == nil && cp != nil && !cp.IsStale(24*time.Hour) {
+			state.State = "crash-recovery"
+			state.CheckpointAge = cp.Age().Round(time.Minute).String()
+			return state
+		}
+	}
+
+	// Check for hooked work (autonomous state)
+	agentID := getAgentIdentity(ctx)
+	if agentID != "" {
+		b := beads.New(ctx.WorkDir)
+		hookedBeads, err := b.List(beads.ListOptions{
+			Status:   beads.StatusHooked,
+			Assignee: agentID,
+			Priority: -1,
+		})
+		if err == nil && len(hookedBeads) > 0 {
+			state.State = "autonomous"
+			state.HookedBead = hookedBeads[0].ID
+			return state
+		}
+		// Also check in_progress beads
+		inProgressBeads, err := b.List(beads.ListOptions{
+			Status:   "in_progress",
+			Assignee: agentID,
+			Priority: -1,
+		})
+		if err == nil && len(inProgressBeads) > 0 {
+			state.State = "autonomous"
+			state.HookedBead = inProgressBeads[0].ID
+			return state
+		}
+	}
+
+	return state
+}
+
+// checkHandoffMarker checks for a handoff marker file and outputs a warning if found.
+// This prevents the "handoff loop" bug where a new session sees /handoff in context
+// and incorrectly runs it again. The marker tells the new session: "handoff is DONE,
+// the /handoff you see in context was from YOUR PREDECESSOR, not a request for you."
+func checkHandoffMarker(workDir string) {
+	markerPath := filepath.Join(workDir, constants.DirRuntime, constants.FileHandoffMarker)
+	data, err := os.ReadFile(markerPath)
+	if err != nil {
+		// No marker = not post-handoff, normal startup
+		return
+	}
+
+	// Marker found - this is a post-handoff session
+	prevSession := strings.TrimSpace(string(data))
+
+	// Remove the marker FIRST so we don't warn twice
+	_ = os.Remove(markerPath)
+
+	// Output prominent warning
+	outputHandoffWarning(prevSession)
+}
+
+// checkHandoffMarkerDryRun checks for handoff marker without removing it (for --dry-run).
+func checkHandoffMarkerDryRun(workDir string) {
+	markerPath := filepath.Join(workDir, constants.DirRuntime, constants.FileHandoffMarker)
+	data, err := os.ReadFile(markerPath)
+	if err != nil {
+		// No marker = not post-handoff, normal startup
+		explain(true, "Post-handoff: no handoff marker found")
+		return
+	}
+
+	// Marker found - this is a post-handoff session
+	prevSession := strings.TrimSpace(string(data))
+	explain(true, fmt.Sprintf("Post-handoff: marker found (predecessor: %s), marker NOT removed in dry-run", prevSession))
+
+	// Output the warning but don't remove marker
+	outputHandoffWarning(prevSession)
+}