fix: width detection prioritizes dynamic sources over config

Config `width` was position #3 in the detection chain, overriding all
dynamic detection (ioctl, process tree, stty, etc). This meant the
statusline couldn't adapt to terminal/pane resizes.

Now config `width` serves two roles:
- Max cap on dynamically detected widths (prevents absurd widths)
- Fallback when all dynamic detection methods fail

Also adds:
- ioctl on stderr (works when stdout is piped)
- stdin JSON `terminal_width` field for Claude Code to pass width
- Distinct diagnostic sources: config_cap, config_fallback, stdin_json

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

src/bin/claude-statusline.rs

@@ -122,8 +122,14 @@ fn main() {
 
     // Detect environment
     let detected_theme = theme::detect_theme(&config);
-    let (term_width, width_source) =
-        width::detect_width_with_source(cli_width, config.global.width, config.global.width_margin);
+    let stdin_width = input_data.workspace.as_ref().and_then(|w| w.terminal_width);
+    let (term_width, width_source) = width::detect_width_with_source(
+        cli_width,
+        config.global.width,
+        config.global.width_margin,
+        stdin_width,
+    );
+
     let tier = width::width_tier(
         term_width,
         config.global.breakpoints.narrow,

src/input.rs

@@ -51,6 +51,7 @@ pub struct CurrentUsage {
 #[serde(default)]
 pub struct Workspace {
     pub project_dir: Option<String>,
+    pub terminal_width: Option<u16>,
 }
 
 #[derive(Debug, Default, Deserialize)]

src/width.rs

@@ -22,9 +22,24 @@ pub fn width_tier(width: u16, narrow_bp: u16, medium_bp: u16) -> WidthTier {
 }
 
 /// Detect terminal width. Memoized for 1 second across renders.
-/// Priority: cli_width > env > config > ioctl > process tree > stty > COLUMNS > tput > 120
-pub fn detect_width(cli_width: Option<u16>, config_width: Option<u16>, config_margin: u16) -> u16 {
-    detect_width_with_source(cli_width, config_width, config_margin).0
+///
+/// Priority chain:
+///   1. `--width` CLI flag (absolute override)
+///   2. `CLAUDE_STATUSLINE_WIDTH` env var (absolute override)
+///   3. stdin JSON `terminal_width` (from Claude Code)
+///   4. ioctl stdout, 5. ioctl stderr, 6. process tree, 7. stty, 8. COLUMNS, 9. tput
+///   10. Config `width` (fallback only)
+///   11. Hardcoded 120
+///
+/// Config `width` also acts as a max cap on dynamic results (items 3-9).
+/// CLI flag and env var are NOT capped — they're explicit user overrides.
+pub fn detect_width(
+    cli_width: Option<u16>,
+    config_width: Option<u16>,
+    config_margin: u16,
+    stdin_width: Option<u16>,
+) -> u16 {
+    detect_width_with_source(cli_width, config_width, config_margin, stdin_width).0
 }
 
 /// Like detect_width but also returns the detection source name (for --dump-state).
@@ -32,6 +47,7 @@ pub fn detect_width_with_source(
     cli_width: Option<u16>,
     config_width: Option<u16>,
     config_margin: u16,
+    stdin_width: Option<u16>,
 ) -> (u16, &'static str) {
     // Check memo first
     if let Ok(guard) = CACHED_WIDTH.lock() {
@@ -42,7 +58,7 @@ pub fn detect_width_with_source(
         }
     }
 
-    let (raw, source) = detect_raw_with_source(cli_width, config_width);
+    let (raw, source) = detect_raw_with_source(cli_width, config_width, stdin_width);
     let effective = raw.saturating_sub(config_margin).max(40);
 
     // Store in memo
@@ -56,15 +72,16 @@ pub fn detect_width_with_source(
 fn detect_raw_with_source(
     cli_width: Option<u16>,
     config_width: Option<u16>,
+    stdin_width: Option<u16>,
 ) -> (u16, &'static str) {
-    // 1. --width CLI flag
+    // 1. --width CLI flag (absolute, not capped)
     if let Some(w) = cli_width {
         if w > 0 {
             return (w, "cli_flag");
         }
     }
 
-    // 2. CLAUDE_STATUSLINE_WIDTH env var
+    // 2. CLAUDE_STATUSLINE_WIDTH env var (absolute, not capped)
     if let Ok(val) = std::env::var("CLAUDE_STATUSLINE_WIDTH") {
         if let Ok(w) = val.parse::<u16>() {
             if w > 0 {
@@ -73,52 +90,92 @@ fn detect_raw_with_source(
         }
     }
 
-    // 3. Config override
+    // 3-9: Dynamic detection, subject to config max cap
+    if let Some((w, source)) = detect_dynamic(stdin_width) {
+        return apply_config_cap(w, source, config_width);
+    }
+
+    // 10. Config width as fallback
     if let Some(w) = config_width {
         if w > 0 {
-            return (w, "config");
+            return (w, "config_fallback");
+        }
+    }
+
+    // 11. Hardcoded fallback
+    (120, "fallback")
+}
+
+/// Try all dynamic detection methods in priority order.
+/// Returns the first successful result.
+fn detect_dynamic(stdin_width: Option<u16>) -> Option<(u16, &'static str)> {
+    // 3. stdin JSON terminal_width (Claude Code passes this)
+    if let Some(w) = stdin_width {
+        if w > 0 {
+            return Some((w, "stdin_json"));
         }
     }
 
     // 4. ioctl(TIOCGWINSZ) on stdout
     if let Some(w) = ioctl_width(libc::STDOUT_FILENO) {
         if w > 0 {
-            return (w, "ioctl");
+            return Some((w, "ioctl_stdout"));
         }
     }
 
-    // 5. Process tree walk: find ancestor with real TTY
+    // 5. ioctl(TIOCGWINSZ) on stderr (often still a TTY when stdout is piped)
+    if let Some(w) = ioctl_width(libc::STDERR_FILENO) {
+        if w > 0 {
+            return Some((w, "ioctl_stderr"));
+        }
+    }
+
+    // 6. Process tree walk: find ancestor with real TTY
     if let Some(w) = process_tree_width() {
         if w > 0 {
-            return (w, "process_tree");
+            return Some((w, "process_tree"));
         }
     }
 
-    // 6. stty size < /dev/tty
+    // 7. stty size < /dev/tty
     if let Some(w) = stty_dev_tty() {
         if w > 0 {
-            return (w, "stty");
+            return Some((w, "stty"));
         }
     }
 
-    // 7. COLUMNS env var
+    // 8. COLUMNS env var
     if let Ok(val) = std::env::var("COLUMNS") {
         if let Ok(w) = val.parse::<u16>() {
             if w > 0 {
-                return (w, "columns_env");
+                return Some((w, "columns_env"));
             }
         }
     }
 
-    // 8. tput cols
+    // 9. tput cols
     if let Some(w) = tput_cols() {
         if w > 0 {
-            return (w, "tput");
+            return Some((w, "tput"));
         }
     }
 
-    // 9. Fallback
-    (120, "fallback")
+    None
+}
+
+/// Apply config width as a max cap on dynamically detected width.
+/// If the detected width exceeds config, clamp it down and report the cap.
+fn apply_config_cap(
+    detected: u16,
+    source: &'static str,
+    config_width: Option<u16>,
+) -> (u16, &'static str) {
+    if let Some(max_w) = config_width {
+        if max_w > 0 && detected > max_w {
+            return (max_w, "config_cap");
+        }
+    }
+    (detected, source)
 }
 
 fn ioctl_width(fd: i32) -> Option<u16> {

statusline.json

@@ -0,0 +1,28 @@
+{
+  "$schema": "./schema.json",
+  "global": {
+    "justify": "spread",
+    "theme": "dark",
+    "responsive": true,
+    "width": 500,
+    "width_margin": 20
+  },
+  "glyphs": {
+    "enabled": true
+  },
+  "layout": "verbose",
+  "sections": {
+    "context_usage": {
+      "enabled": true
+    },
+    "context_trend": {
+      "enabled": true
+    },
+    "cost_trend": {
+      "enabled": true
+    },
+    "load": {
+      "enabled": false
+    }
+  }
+}