feat(prime): add --stealth flag for flush-only workflow

Add a `--stealth` flag to `bd prime` that outputs a simplified
workflow using only `bd sync --flush-only`, omitting all git
operations (commit, push, pull).

This addresses use cases where git operations need to be deferred
or handled separately from the bd workflow (e.g. bd init --stealth),
where committing files is may not desired as part of the Claude
conversation.

In stealth mode, the close protocol shows only the flush step.

Includes tests for current and existing functionality.

To make testing easier,
refactor output functions to accept `io.Writer` parameters
instead of writing directly to `os.Stdout`,
and convert `isEphemeralBranch` from a function to a
variable for stubbing.

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

cmd/bd/prime.go

@@ -3,6 +3,7 @@ package main
 import (
 	"encoding/json"
 	"fmt"
+	"io"
 	"os"
 	"os/exec"
 	"path/filepath"
@@ -13,8 +14,9 @@ import (
 )
 
 var (
-	primeFullMode bool
-	primeMCPMode  bool
+	primeFullMode    bool
+	primeMCPMode     bool
+	primeStealthMode bool
 )
 
 var primeCmd = &cobra.Command{
@@ -47,8 +49,8 @@ agents from forgetting bd workflow after context compaction.`,
 			mcpMode = true
 		}
 
-		// Output workflow context (adaptive based on MCP)
-		if err := outputPrimeContext(mcpMode); err != nil {
+		// Output workflow context (adaptive based on MCP and stealth mode)
+		if err := outputPrimeContext(os.Stdout, mcpMode, primeStealthMode); err != nil {
 			// Suppress all errors - silent exit with success
 			// Never write to stderr (breaks Windows compatibility)
 			os.Exit(0)
@@ -59,6 +61,7 @@ agents from forgetting bd workflow after context compaction.`,
 func init() {
 	primeCmd.Flags().BoolVar(&primeFullMode, "full", false, "Force full CLI output (ignore MCP detection)")
 	primeCmd.Flags().BoolVar(&primeMCPMode, "mcp", false, "Force MCP mode (minimal output)")
+	primeCmd.Flags().BoolVar(&primeStealthMode, "stealth", false, "Stealth mode (no git operations, flush only)")
 	rootCmd.AddCommand(primeCmd)
 }
 
@@ -104,7 +107,7 @@ func isMCPActive() bool {
 }
 
 // isEphemeralBranch detects if current branch has no upstream (ephemeral/local-only)
-func isEphemeralBranch() bool {
+var isEphemeralBranch = func() bool {
 	// git rev-parse --abbrev-ref --symbolic-full-name @{u}
 	// Returns error code 128 if no upstream configured
 	cmd := exec.Command("git", "rev-parse", "--abbrev-ref", "--symbolic-full-name", "@{u}")
@@ -113,19 +116,22 @@ func isEphemeralBranch() bool {
 }
 
 // outputPrimeContext outputs workflow context in markdown format
-func outputPrimeContext(mcpMode bool) error {
+func outputPrimeContext(w io.Writer, mcpMode bool, stealthMode bool) error {
 	if mcpMode {
-		return outputMCPContext()
+		return outputMCPContext(w, stealthMode)
 	}
-	return outputCLIContext()
+	return outputCLIContext(w, stealthMode)
 }
 
 // outputMCPContext outputs minimal context for MCP users
-func outputMCPContext() error {
+func outputMCPContext(w io.Writer, stealthMode bool) error {
 	ephemeral := isEphemeralBranch()
 
 	var closeProtocol string
-	if ephemeral {
+	if stealthMode {
+		// Stealth mode: only flush to JSONL as there's nothing to commit.
+		closeProtocol = "Before saying \"done\": bd sync --flush-only"
+	} else if ephemeral {
 		closeProtocol = "Before saying \"done\": git status → git add → bd sync --from-main → git commit (no push - ephemeral branch)"
 	} else {
 		closeProtocol = "Before saying \"done\": git status → git add → bd sync → git commit → bd sync → git push"
@@ -143,12 +149,12 @@ func outputMCPContext() error {
 
 Start: Check ` + "`ready`" + ` tool for available work.
 `
-	fmt.Print(context)
+	_, _ = fmt.Fprint(w, context)
 	return nil
 }
 
 // outputCLIContext outputs full CLI reference for non-MCP users
-func outputCLIContext() error {
+func outputCLIContext(w io.Writer, stealthMode bool) error {
 	ephemeral := isEphemeralBranch()
 
 	var closeProtocol string
@@ -156,7 +162,17 @@ func outputCLIContext() error {
 	var syncSection string
 	var completingWorkflow string
 
-	if ephemeral {
+	if stealthMode {
+		// Stealth mode: only flush to JSONL, no git operations
+		closeProtocol = `[ ] bd sync --flush-only    (export beads to JSONL only)`
+		syncSection = `### Sync & Collaboration
+- ` + "`bd sync --flush-only`" + ` - Export to JSONL`
+		completingWorkflow = `**Completing work:**
+` + "```bash" + `
+bd close <id1> <id2> ...    # Close all completed issues at once
+bd sync --flush-only        # Export to JSONL
+` + "```"
+	} else if ephemeral {
 		closeProtocol = `[ ] 1. git status              (check what changed)
 [ ] 2. git add <files>         (stage code changes)
 [ ] 3. bd sync --from-main     (pull beads updates from main)
@@ -258,6 +274,6 @@ bd create --title="Write tests for X" --type=task
 bd dep add beads-yyy beads-xxx  # Tests depend on Feature (Feature blocks tests)
 ` + "```" + `
 `
-	fmt.Print(context)
+	_, _ = fmt.Fprint(w, context)
 	return nil
 }