feat: complete Rust port of claude-statusline

Port the entire 2236-line bash statusline script to Rust.
Implements all 25 sections, 3-phase layout engine (render, priority
drop, flex/justify), file-based caching with flock, 9-level terminal
width detection, trend sparklines, and deep-merge JSON config.

Release binary: 864K with LTO. Render time: <1ms warm.

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

src/layout/mod.rs

@@ -0,0 +1,177 @@
+pub mod flex;
+pub mod justify;
+pub mod priority;
+
+use crate::config::{Config, JustifyMode, LayoutValue};
+use crate::section::{self, RenderContext, SectionOutput};
+
+/// A section that survived priority drops and has rendered output.
+pub struct ActiveSection {
+    pub id: String,
+    pub output: SectionOutput,
+    pub priority: u8,
+    pub is_spacer: bool,
+    pub is_flex: bool,
+}
+
+/// Resolve layout: preset lookup with optional responsive override.
+pub fn resolve_layout(config: &Config, term_width: u16) -> Vec<Vec<String>> {
+    match &config.layout {
+        LayoutValue::Preset(name) => {
+            let effective = if config.global.responsive {
+                responsive_preset(term_width, &config.global.breakpoints)
+            } else {
+                name.as_str()
+            };
+            config
+                .presets
+                .get(effective)
+                .or_else(|| config.presets.get(name.as_str()))
+                .cloned()
+                .unwrap_or_else(|| vec![vec!["model".into(), "project".into()]])
+        }
+        LayoutValue::Custom(lines) => lines.clone(),
+    }
+}
+
+fn responsive_preset(width: u16, bp: &crate::config::Breakpoints) -> &'static str {
+    if width < bp.narrow {
+        "dense"
+    } else if width < bp.medium {
+        "standard"
+    } else {
+        "verbose"
+    }
+}
+
+/// Full render: resolve layout, render each line, join with newlines.
+pub fn render_all(ctx: &RenderContext) -> String {
+    let layout = resolve_layout(ctx.config, ctx.term_width);
+    let separator = &ctx.config.global.separator;
+
+    let lines: Vec<String> = layout
+        .iter()
+        .filter_map(|line_ids| render_line(line_ids, ctx, separator))
+        .collect();
+
+    lines.join("\n")
+}
+
+/// Render a single layout line.
+/// Three phases: render all -> priority drop -> flex/justify.
+fn render_line(section_ids: &[String], ctx: &RenderContext, separator: &str) -> Option<String> {
+    // Phase 1: Render all sections, collect active ones
+    let mut active: Vec<ActiveSection> = Vec::new();
+
+    for id in section_ids {
+        if let Some(output) = section::render_section(id, ctx) {
+            if output.raw.is_empty() && !section::is_spacer(id) {
+                continue;
+            }
+
+            let (prio, is_flex) = section_meta(id, ctx.config);
+            active.push(ActiveSection {
+                id: id.clone(),
+                output,
+                priority: prio,
+                is_spacer: section::is_spacer(id),
+                is_flex,
+            });
+        }
+    }
+
+    if active.is_empty() || active.iter().all(|s| s.is_spacer) {
+        return None;
+    }
+
+    // Phase 2: Priority drop if overflowing
+    let mut active = priority::priority_drop(active, ctx.term_width, separator);
+
+    // Phase 3: Flex expand or justify
+    let line = if ctx.config.global.justify != JustifyMode::Left
+        && !active.iter().any(|s| s.is_spacer)
+        && active.len() > 1
+    {
+        justify::justify(
+            &active,
+            ctx.term_width,
+            separator,
+            ctx.config.global.justify,
+        )
+    } else {
+        flex::flex_expand(&mut active, ctx, separator);
+        assemble_left(&active, separator, ctx.color_enabled)
+    };
+
+    Some(line)
+}
+
+/// Left-aligned assembly with separator dimming and spacer suppression.
+fn assemble_left(active: &[ActiveSection], separator: &str, color_enabled: bool) -> String {
+    let mut output = String::new();
+    let mut prev_is_spacer = false;
+
+    for (i, sec) in active.iter().enumerate() {
+        if i > 0 && !prev_is_spacer && !sec.is_spacer {
+            if color_enabled {
+                output.push_str(&format!(
+                    "{}{separator}{}",
+                    crate::color::DIM,
+                    crate::color::RESET
+                ));
+            } else {
+                output.push_str(separator);
+            }
+        }
+        output.push_str(&sec.output.ansi);
+        prev_is_spacer = sec.is_spacer;
+    }
+
+    output
+}
+
+/// Look up section priority and flex from config.
+fn section_meta(id: &str, config: &Config) -> (u8, bool) {
+    if section::is_spacer(id) {
+        return (1, true);
+    }
+
+    macro_rules! meta_base {
+        ($section:expr) => {
+            ($section.priority, $section.flex)
+        };
+    }
+    macro_rules! meta_flat {
+        ($section:expr) => {
+            ($section.base.priority, $section.base.flex)
+        };
+    }
+
+    match id {
+        "model" => meta_base!(config.sections.model),
+        "provider" => meta_base!(config.sections.provider),
+        "project" => meta_flat!(config.sections.project),
+        "vcs" => meta_flat!(config.sections.vcs),
+        "beads" => meta_flat!(config.sections.beads),
+        "context_bar" => meta_flat!(config.sections.context_bar),
+        "context_usage" => meta_flat!(config.sections.context_usage),
+        "context_remaining" => meta_flat!(config.sections.context_remaining),
+        "tokens_raw" => meta_flat!(config.sections.tokens_raw),
+        "cache_efficiency" => meta_base!(config.sections.cache_efficiency),
+        "cost" => meta_flat!(config.sections.cost),
+        "cost_velocity" => meta_base!(config.sections.cost_velocity),
+        "token_velocity" => meta_base!(config.sections.token_velocity),
+        "cost_trend" => meta_flat!(config.sections.cost_trend),
+        "context_trend" => meta_flat!(config.sections.context_trend),
+        "lines_changed" => meta_base!(config.sections.lines_changed),
+        "duration" => meta_base!(config.sections.duration),
+        "tools" => meta_flat!(config.sections.tools),
+        "turns" => meta_flat!(config.sections.turns),
+        "load" => meta_flat!(config.sections.load),
+        "version" => meta_base!(config.sections.version),
+        "time" => meta_flat!(config.sections.time),
+        "output_style" => meta_base!(config.sections.output_style),
+        "hostname" => meta_base!(config.sections.hostname),
+        _ => (2, false), // custom sections default
+    }
+}