feat(v0.5.2): cross-workspace context section in seed CLAUDE.md

Adds a concise "## Cross-Workspace Context" section to both the
task and project CLAUDE.md seed templates. Teaches the agent to
inspect related workspaces with the new commands before making
changes:

  ctask list --all          discover all workspaces, including archived
  ctask info <workspace>    view metadata and status of any workspace
  ctask notes <workspace>   read another workspace's notes.md
  ctask path <workspace>    get the filesystem path to inspect files

Closes the v0.5.2 design loop: ctask exposes workspace context
through CLI commands and lets agents consume it themselves. The
seed text is read-only by convention — the section explicitly
asks the agent to treat other workspaces as read-only unless the
user grants modification rights.

Applies to newly created workspaces only. Existing workspaces
keep their current CLAUDE.md (per spec: no retroactive overwrite).
Users with custom seed directories see this only if they update
their seeds.

internal/seed/templates.go

@@ -26,6 +26,22 @@ This is a ctask workspace. Prefer operating inside this directory unless explici
 - Record important assumptions and actions in notes.md
 - Keep the workspace root clean -- use subdirectories for organization
 
+## Cross-Workspace Context
+
+Related work may exist in other ctask workspaces. For project continuation,
+migration, debugging, or building on prior work, inspect related workspaces
+before making changes.
+
+Available commands:
+
+  ctask list --all          discover all workspaces, including archived
+  ctask info <workspace>    view metadata and status of any workspace
+  ctask notes <workspace>   read another workspace's notes.md
+  ctask path <workspace>    get the filesystem path to inspect files directly
+
+Treat other workspaces as read-only unless the user explicitly asks you to
+modify them.
+
 ## Session Handoff
 
 Before ending a session, append a brief summary to notes.md with:
@@ -84,6 +100,22 @@ Do not initialize additional git repositories inside the project subdirectory
 or any other subdirectory. If you need to check git status or make commits,
 the repo root is the workspace root.
 
+## Cross-Workspace Context
+
+Related work may exist in other ctask workspaces. For project continuation,
+migration, debugging, or building on prior work, inspect related workspaces
+before making changes.
+
+Available commands:
+
+  ctask list --all          discover all workspaces, including archived
+  ctask info <workspace>    view metadata and status of any workspace
+  ctask notes <workspace>   read another workspace's notes.md
+  ctask path <workspace>    get the filesystem path to inspect files directly
+
+Treat other workspaces as read-only unless the user explicitly asks you to
+modify them.
+
 ## Session Handoff
 
 Before ending a session, append a brief summary to notes.md with:

internal/seed/templates_test.go

@@ -89,6 +89,40 @@ func TestClaudeMDProjectDescribesWorkspaceStructure(t *testing.T) {
 	}
 }
 
+func TestClaudeMDContainsCrossWorkspaceSection(t *testing.T) {
+	// v0.5.2: both templates teach agents to use ctask's read-only context
+	// commands before starting work.
+	content := ClaudeMD("ignored", "ignored", "ignored")
+	for _, must := range []string{
+		"## Cross-Workspace Context",
+		"ctask list --all",
+		"ctask info <workspace>",
+		"ctask notes <workspace>",
+		"ctask path <workspace>",
+		"Treat other workspaces as read-only",
+	} {
+		if !strings.Contains(content, must) {
+			t.Errorf("task CLAUDE.md missing cross-workspace marker %q", must)
+		}
+	}
+}
+
+func TestClaudeMDProjectContainsCrossWorkspaceSection(t *testing.T) {
+	content := ClaudeMDProject()
+	for _, must := range []string{
+		"## Cross-Workspace Context",
+		"ctask list --all",
+		"ctask info <workspace>",
+		"ctask notes <workspace>",
+		"ctask path <workspace>",
+		"Treat other workspaces as read-only",
+	} {
+		if !strings.Contains(content, must) {
+			t.Errorf("project CLAUDE.md missing cross-workspace marker %q", must)
+		}
+	}
+}
+
 func TestNotesMDIsASCII(t *testing.T) {
 	content := NotesMD("test title")
 	for i, b := range []byte(content) {