feat(cli): render library progress with indicatif

The CLI owns the terminal now: TermProgress turns the library's
Progress events into bars and spinners on stderr (hidden by indicatif
when stderr is not a terminal).  Named transfers (OCI layers, kernel,
tarball) render as byte bars, extraction and initramfs as file-count
spinners.

crates/ecr-cli/Cargo.toml

@@ -21,3 +21,6 @@ clap = { version = "4", features = ["derive", "env"] }
 
 # Error handling
 anyhow = "1"
+
+# Progress bar rendering of library progress events
+indicatif = "0.18"

crates/ecr-cli/src/main.rs

@@ -1,4 +1,5 @@
 mod cli;
+mod progress;
 
 use std::path::{Path, PathBuf};
 
@@ -11,6 +12,7 @@ use ecr::config::Config;
 use ecr::exec::ExecOptions;
 use ecr::mount::BindTarget;
 use ecr::{kernel, qemu, qemu_vm, utils, veprintln, verbose, PrepareRequest, RootfsCache};
+use progress::TermProgress;
 
 fn main() -> Result<()> {
     let args = Args::parse();
@@ -18,6 +20,9 @@ fn main() -> Result<()> {
     // Initialise verbosity before anything else so all downstream code can use veprintln!.
     verbose::set(args.verbose);
 
+    // Render library progress (bars/spinners) on the terminal
+    let progress = TermProgress::new();
+
     // Load config file
     let config = Config::load()?;
 
@@ -38,7 +43,7 @@ fn main() -> Result<()> {
         arch: args.arch.clone().unwrap_or_default(),
         no_cache: args.no_cache,
     };
-    let rootfs = cache.prepare(&request, &ecr::NoProgress)?;
+    let rootfs = cache.prepare(&request, &progress)?;
 
     // Branch based on --kernel flag
     // Option<Option<PathBuf>> (require_equals: the value must use =PATH syntax
@@ -63,7 +68,7 @@ fn main() -> Result<()> {
             }
             None => {
                 veprintln!("QEMU mode: downloading default kernel...");
-                kernel::get_default_kernel(cache.dir(), &arch, &ecr::NoProgress)?
+                kernel::get_default_kernel(cache.dir(), &arch, &progress)?
             }
         };
 
@@ -81,7 +86,7 @@ fn main() -> Result<()> {
                 arch: arch.clone(),
                 command,
             },
-            &ecr::NoProgress,
+            &progress,
         );
 
         // Cleanup happens automatically via tempfile

crates/ecr-cli/src/progress.rs

@@ -0,0 +1,91 @@
+//! Terminal rendering of library progress events (indicatif-backed).
+//!
+//! This is CLI-owned UI: the library only emits [`Progress`] events,
+//! and everything drawn on the terminal lives here.  indicatif hides
+//! all output when stderr is not a terminal.
+
+use ecr::progress::{Progress, Unit};
+use indicatif::{ProgressBar, ProgressStyle};
+use std::sync::Mutex;
+
+/// Renders sequential library operations as bars and spinners on stderr.
+pub struct TermProgress {
+    bar: Mutex<Option<ProgressBar>>,
+}
+
+impl TermProgress {
+    pub fn new() -> Self {
+        TermProgress {
+            bar: Mutex::new(None),
+        }
+    }
+}
+
+impl Default for TermProgress {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl Drop for TermProgress {
+    fn drop(&mut self) {
+        self.finish();
+    }
+}
+
+impl Progress for TermProgress {
+    fn begin(&self, label: &str, unit: Unit, total: Option<u64>) {
+        let mut slot = self.bar.lock().unwrap();
+        // The library's `begin` implicitly ends the previous operation.
+        if let Some(prev) = slot.take() {
+            prev.finish_and_clear();
+        }
+
+        let bar = match (unit, total) {
+            (Unit::Bytes, Some(total)) => {
+                let pb = ProgressBar::new(total);
+                pb.set_style(
+                    ProgressStyle::default_bar()
+                        .template("{spinner:.green} [{elapsed_precise}] [{bar:40.cyan/blue}] {msg} {bytes}/{total_bytes} ({eta})")
+                        .unwrap()
+                        .progress_chars("#>-"),
+                );
+                pb.set_message(label.to_string());
+                pb
+            }
+            (Unit::Bytes, None) => {
+                let pb = ProgressBar::new_spinner();
+                pb.set_style(
+                    ProgressStyle::default_spinner()
+                        .template("{spinner:.green} {msg} ({bytes})")
+                        .unwrap(),
+                );
+                pb.set_message(label.to_string());
+                pb
+            }
+            (Unit::Files, _) => {
+                let pb = ProgressBar::new_spinner();
+                pb.set_style(
+                    ProgressStyle::default_spinner()
+                        .template("{spinner:.green} {msg} ({pos} files)")
+                        .unwrap(),
+                );
+                pb.set_message(label.to_string());
+                pb
+            }
+        };
+        *slot = Some(bar);
+    }
+
+    fn advance(&self, n: u64) {
+        if let Some(bar) = &*self.bar.lock().unwrap() {
+            bar.inc(n);
+        }
+    }
+
+    fn finish(&self) {
+        if let Some(bar) = self.bar.lock().unwrap().take() {
+            bar.finish_and_clear();
+        }
+    }
+}