feat: display DEFCON posture in banner + prompt

Reads BASCULE_DEFCON_LEVEL from env. At DEFCON <5:
  Banner: DEFCON level + label (RESTRICTED/CRITICAL/LOCKDOWN) + reason
  Prompt: [restricted] at DEFCON 3, [DEFCON] at ≤2

DEFCON 5 (peacetime): no DEFCON line in banner, normal prompt.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

gsh/src/human.rs

@@ -162,6 +162,25 @@ fn print_banner(session: &SessionState) {
             _ => session.risk_level.clone(),
         },
         "║".bright_blue());
+
+    // DEFCON line — only shown when not peacetime
+    if session.defcon_level < 5 {
+        let defcon_label = match session.defcon_level {
+            1 => "LOCKDOWN".red().to_string(),
+            2 => "CRITICAL".red().to_string(),
+            3 => "RESTRICTED".yellow().to_string(),
+            4 => "ELEVATED".yellow().to_string(),
+            _ => "PEACETIME".green().to_string(),
+        };
+        println!("{}  DEFCON:    {:<44}{}", "║".bright_blue(),
+            format!("{} — {}", session.defcon_level, defcon_label),
+            "║".bright_blue());
+        if let Some(ref reason) = session.defcon_reason {
+            let truncated = if reason.len() > 42 { format!("{}...", &reason[..39]) } else { reason.clone() };
+            println!("{}  Reason:    {:<44}{}", "║".bright_blue(), truncated, "║".bright_blue());
+        }
+    }
+
     println!("{}", "╚══════════════════════════════════════════════════════════╝".bright_blue());
     println!();
 }
@@ -193,11 +212,18 @@ fn print_summary(session: &SessionState) {
 }
 
 fn build_prompt(session: &SessionState) -> DefaultPrompt {
-    let risk_indicator = match session.risk_level.as_str() {
+    // DEFCON overrides the risk indicator when elevated
+    let risk_indicator = if session.defcon_level <= 2 {
+        "[DEFCON]"
+    } else if session.defcon_level == 3 {
+        "[restricted]"
+    } else {
+        match session.risk_level.as_str() {
             "baseline" | "standard" | "ungoverned" => "[governed]",
             "elevated" => "[elevated]",
             "high" | "critical" => "[HIGH]",
             _ => "[governed]",
+        }
     };
 
     let short_name = session.display_name.split('@').next().unwrap_or(&session.display_name);

libgsh/src/session.rs

@@ -9,6 +9,8 @@ pub struct SessionState {
     pub principal: String,
     pub display_name: String,
     pub risk_level: String,
+    pub defcon_level: i32,
+    pub defcon_reason: Option<String>,
     pub started_at: chrono::DateTime<chrono::Utc>,
     pub expires_at: Option<chrono::DateTime<chrono::Utc>>,
     pub governed_count: u32,
@@ -40,12 +42,18 @@ impl SessionState {
         let display_name = std::env::var("BASCULE_DISPLAY_NAME")
             .unwrap_or_else(|_| display_name_from_did(&principal));
 
+        let defcon_level = std::env::var("BASCULE_DEFCON_LEVEL")
+            .ok().and_then(|v| v.parse().ok()).unwrap_or(5);
+        let defcon_reason = std::env::var("BASCULE_DEFCON_REASON").ok();
+
         Self {
             ac_id: ac.context_id.clone(),
             corpus_cid: corpus_cid.to_string(),
             principal,
             display_name,
-            risk_level: "standard".to_string(), // TODO: read from AC when broker embeds it
+            risk_level: "standard".to_string(),
+            defcon_level,
+            defcon_reason,
             started_at: chrono::Utc::now(),
             expires_at,
             governed_count: 0,
@@ -60,12 +68,18 @@ impl SessionState {
         let principal = whoami();
         let display_name = std::env::var("BASCULE_DISPLAY_NAME")
             .unwrap_or_else(|_| principal.clone());
+        let defcon_level = std::env::var("BASCULE_DEFCON_LEVEL")
+            .ok().and_then(|v| v.parse().ok()).unwrap_or(5);
+        let defcon_reason = std::env::var("BASCULE_DEFCON_REASON").ok();
+
         Self {
             ac_id: "ungoverned".to_string(),
             corpus_cid: corpus_cid.to_string(),
             principal,
             display_name,
             risk_level: "ungoverned".to_string(),
+            defcon_level,
+            defcon_reason,
             started_at: chrono::Utc::now(),
             expires_at: None,
             governed_count: 0,