iter emit-ir-staticlib: ail emit-ir --emit=staticlib (M1 fieldtest spec_gap#2)

Restores the Decision-5 IR-readability affordance for main-free
kernels: ail emit-ir gains --emit=staticlib, symmetric with
ail build, reusing the M1-audited Target::StaticLib path via a new
one-line lower_workspace_staticlib convenience. Zero-export guard
byte-identical to build_staticlib's. DESIGN.md widened (not
narrowed) + a pre-existing M1 synopsis omission corrected. 3 new
E2E tests; no fixture minted, no doc pin (E2E is the coverage).
Plan 03493c9.

crates/ail/src/main.rs

@@ -116,6 +116,14 @@ enum Cmd {
         path: PathBuf,
         #[arg(short, long)]
         out: Option<PathBuf>,
+        /// IR shape. `exe` (default): whole-program IR (requires an
+        /// entry `main`). `staticlib`: kernel IR for a `main`-free
+        /// module — one external C forwarder per `(export "<sym>")`
+        /// fn, no `@main` (Embedding ABI M1). Same `Target` the
+        /// `build --emit=staticlib` path uses; output is the IR text
+        /// (stdout, or `-o <file>`), not archives.
+        #[arg(long, default_value = "exe", value_parser = ["exe", "staticlib"])]
+        emit: String,
     },
     /// Full pipeline: check + emit-ir + clang -> binary.
     Build {
@@ -637,7 +645,7 @@ fn main() -> Result<()> {
                 );
             }
         }
-        Cmd::EmitIr { path, out } => {
+        Cmd::EmitIr { path, out, emit } => {
             // Iter 5c: workspace lowering. For single-module programs the
             // workspace is effectively a trivial workspace with one module.
             let ws = load_workspace_human(&path)?;
@@ -687,7 +695,18 @@ fn main() -> Result<()> {
             };
             let ws = ailang_check::monomorphise_workspace(&ws)
                 .map_err(|e| anyhow::anyhow!("monomorphise_workspace: {e}"))?;
-            let ir = ailang_codegen::lower_workspace(&ws)?;
+            let ir = if emit == "staticlib" {
+                let has_export = ws.modules.values().any(|m| m.defs.iter().any(|d|
+                    matches!(d, ailang_core::Def::Fn(f) if f.export.is_some())));
+                if !has_export {
+                    anyhow::bail!(
+                        "staticlib target needs at least one `(export \"<sym>\")` fn"
+                    );
+                }
+                ailang_codegen::lower_workspace_staticlib(&ws)?
+            } else {
+                ailang_codegen::lower_workspace(&ws)?
+            };
             match out {
                 Some(p) => {
                     std::fs::write(&p, ir)?;