cli: new books dirs get a SessionStart hook that checks the viewer

The viewer offer (open_at_start) lived only in AGENTS.md, so it depended
on the agent remembering it on its first turn. The scaffold's
.claude/settings.json now runs just gui-status at session start and hands
the agent the result plus open_at_start.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Tpv1gBaepKjQiAVJqejGbA

crates/ledger-cli/src/main.rs

@@ -15,7 +15,8 @@
 //!    `.gitignore`, and `books-data/`.
 //! 3. Registers the MCP server for this directory only: `.mcp.json`, plus
 //!    `.claude/settings.json` approving it, so Claude Code loads the tools
-//!    without `claude mcp add` or a prompt.
+//!    without `claude mcp add` or a prompt. The same settings carry a
+//!    SessionStart hook that checks whether the viewer is open.
 //! 4. `git init`s the directory (its history is the archive) and commits.
 //! 5. Starts `claude` in the directory with the onboarding prompt, unless
 //!    `--no-start` or there's no terminal. With `--codex`, registers the
@@ -363,11 +364,25 @@ fn mcp_json(ledger_mcp: &Path, books: &Path) -> String {
 
 /// `.claude/settings.json`: approve this directory's server, and its tools,
 /// so the first session starts working instead of asking. The server still
-/// previews every posting for the human to confirm.
+/// previews every posting for the human to confirm. A SessionStart hook
+/// checks the viewer and hands the agent `[viewer] open_at_start`, so the
+/// offer to open it doesn't hang on the agent remembering AGENTS.md.
 const CLAUDE_SETTINGS: &str = r#"{
   "enabledMcpjsonServers": ["wanderbooks"],
   "permissions": {
     "allow": ["mcp__wanderbooks"]
+  },
+  "hooks": {
+    "SessionStart": [
+      {
+        "hooks": [
+          {
+            "type": "command",
+            "command": "cd \"$CLAUDE_PROJECT_DIR\" && if just gui-status >/dev/null 2>&1; then echo 'wanderbooks viewer: open.'; else echo \"wanderbooks viewer: CLOSED. [viewer] open_at_start = $(sed -n 's/^open_at_start *= *//p' wanderbooks.toml). Act on this at the top of your first reply, before anything else: \\\"ask\\\" -> offer to open it (just gui); \\\"always\\\" -> run just gui; \\\"never\\\" -> say nothing.\"; fi"
+          }
+        ]
+      }
+    ]
   }
 }
 "#;

crates/ledger-cli/tests/init.rs

@@ -97,6 +97,11 @@ fn the_server_is_registered_for_this_dir() {
         settings["enabledMcpjsonServers"],
         serde_json::json!(["wanderbooks"])
     );
+    // Every session starts by checking the viewer against open_at_start.
+    let hook = settings["hooks"]["SessionStart"][0]["hooks"][0]["command"]
+        .as_str()
+        .expect("SessionStart hook command");
+    assert!(hook.contains("just gui-status") && hook.contains("open_at_start"));
     // The justfile opens this dir's books in the GUI.
     let just = fs::read_to_string(books.join("justfile")).unwrap();
     assert!(just.contains("ledger-gui\" --data-dir \"{{justfile_directory()}}/books-data\""));