fix: shutdown safety, CLI hardening, exit code collision

Shutdown signal improvements:
- Upgrade ShutdownSignal from Relaxed to Release/Acquire ordering.
  Relaxed was technically sufficient for a single flag but
  Release/Acquire is the textbook correct pattern and ensures
  visibility guarantees across threads without relying on x86 TSO.
- Add double Ctrl+C support to all three signal handlers (ingest,
  embed, sync). First Ctrl+C sets cooperative flag with user message;
  second Ctrl+C force-exits with code 130 (standard SIGINT convention).

CLI hardening:
- LORE_ROBOT env var now checks for truthy values (!empty, !="0",
  !="false") instead of mere existence. Setting LORE_ROBOT=0 or
  LORE_ROBOT=false no longer activates robot mode.
- Replace unreachable!() in color mode match with defensive warning
  and fallback to auto. Clap validates the values but defense in depth
  prevents panics if the value_parser is ever changed.
- Replace unreachable!() in completions shell match with proper error
  return for unsupported shells.

Exit code collision fix:
- ConfigNotFound was mapped to exit code 2 (error.rs:56) which
  collided with handle_clap_error() also using exit code 2 for parse
  errors. Agents calling lore --robot could not distinguish "bad
  arguments" from "missing config file."
- Restore ConfigNotFound to exit code 20 (its original dedicated code).
- Update robot-docs exit code table: code 2 = "Usage error", code 20 =
  "Config not found".

Build script:
- Track .git/refs/heads directory for Cargo rebuild triggers. Ensures
  GIT_HASH env var updates when branch refs change, not just HEAD.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

build.rs

@@ -7,4 +7,5 @@ fn main() {
         .unwrap_or_default();
     println!("cargo:rustc-env=GIT_HASH={}", hash.trim());
     println!("cargo:rerun-if-changed=.git/HEAD");
+    println!("cargo:rerun-if-changed=.git/refs/heads");
 }

src/cli/mod.rs

@@ -76,7 +76,9 @@ impl Cli {
         let args: Vec<String> = std::env::args().collect();
         args.iter()
             .any(|a| a == "--robot" || a == "-J" || a == "--json")
-            || std::env::var("LORE_ROBOT").is_ok()
+            || std::env::var("LORE_ROBOT")
+                .ok()
+                .is_some_and(|v| !v.is_empty() && v != "0" && v != "false")
             || !std::io::stdout().is_terminal()
     }
 }

src/core/error.rs

@@ -53,7 +53,7 @@ impl ErrorCode {
     pub fn exit_code(&self) -> i32 {
         match self {
             Self::InternalError => 1,
-            Self::ConfigNotFound => 2,
+            Self::ConfigNotFound => 20,
             Self::ConfigInvalid => 3,
             Self::TokenNotSet => 4,
             Self::GitLabAuthFailed => 5,

src/core/shutdown.rs

@@ -19,11 +19,11 @@ impl ShutdownSignal {
     }
 
     pub fn cancel(&self) {
-        self.cancelled.store(true, Ordering::Relaxed);
+        self.cancelled.store(true, Ordering::Release);
     }
 
     pub fn is_cancelled(&self) -> bool {
-        self.cancelled.load(Ordering::Relaxed)
+        self.cancelled.load(Ordering::Acquire)
     }
 }
 

src/main.rs

@@ -134,7 +134,9 @@ async fn main() {
         "never" => console::set_colors_enabled(false),
         "always" => console::set_colors_enabled(true),
         "auto" => {}
-        _ => unreachable!(),
+        other => {
+            eprintln!("Warning: unknown color mode '{}', using auto", other);
+        }
     }
 
     let quiet = cli.quiet;
@@ -664,7 +666,10 @@ async fn handle_ingest(
     let signal_for_handler = signal.clone();
     tokio::spawn(async move {
         let _ = tokio::signal::ctrl_c().await;
+        eprintln!("\nInterrupted, finishing current batch... (Ctrl+C again to force quit)");
         signal_for_handler.cancel();
+        let _ = tokio::signal::ctrl_c().await;
+        std::process::exit(130);
     });
 
     let ingest_result: std::result::Result<(), Box<dyn std::error::Error>> = async {
@@ -1264,7 +1269,9 @@ fn handle_completions(shell: &str) -> Result<(), Box<dyn std::error::Error>> {
         "zsh" => Shell::Zsh,
         "fish" => Shell::Fish,
         "powershell" => Shell::PowerShell,
-        _ => unreachable!(),
+        other => {
+            return Err(format!("Unsupported shell: {other}").into());
+        }
     };
 
     let mut cmd = Cli::command();
@@ -1522,7 +1529,10 @@ async fn handle_embed(
     let signal_for_handler = signal.clone();
     tokio::spawn(async move {
         let _ = tokio::signal::ctrl_c().await;
+        eprintln!("\nInterrupted, finishing current batch... (Ctrl+C again to force quit)");
         signal_for_handler.cancel();
+        let _ = tokio::signal::ctrl_c().await;
+        std::process::exit(130);
     });
 
     let result = run_embed(&config, full, retry_failed, None, &signal).await?;
@@ -1573,7 +1583,10 @@ async fn handle_sync_cmd(
     let signal_for_handler = signal.clone();
     tokio::spawn(async move {
         let _ = tokio::signal::ctrl_c().await;
+        eprintln!("\nInterrupted, finishing current batch... (Ctrl+C again to force quit)");
         signal_for_handler.cancel();
+        let _ = tokio::signal::ctrl_c().await;
+        std::process::exit(130);
     });
 
     let start = std::time::Instant::now();