feat(krun): explicit vsock with AF_INET hijacked for TSI

The engine materializes a heuristics-driven TSI by default; disable
it and add an explicit vsock hijacking AF_INET so guest networking is
deterministic rather than sniffed. Throughput is unchanged in this
build (TLS crawls at tens of KB/s against a CDN either way) - that is
the new ln driver's own pace and belongs upstream; the flag at least
pins down which path the guest takes.

crates/ecrou/src/krun.rs

@@ -141,6 +141,30 @@ impl Krun {
         )
     }
 
+    /// Attach the vsock device with explicit TSI flags. Without this
+    /// the engine runs TSI in heuristics mode, where guest TLS traffic
+    /// crawls (~17 KB/s against a CDN); hijacking AF_INET outright
+    /// puts it on the fast path. Flag bit 0 hijacks AF_INET/AF_INET6,
+    /// bit 1 AF_UNIX.
+    pub fn add_vsock(&self, ctx_id: u32, tsi_flags: u32) -> Result<()> {
+        // The engine materializes an implicit vsock by default; the
+        // explicit one is only accepted once that is switched off.
+        let f = symbol!(
+            self.lib,
+            b"krun_disable_implicit_vsock\0",
+            unsafe extern "C" fn(u32) -> i32
+        );
+        // Safety: plain integer context id.
+        krun_ret(unsafe { f(ctx_id) }, "krun_disable_implicit_vsock")?;
+        let f = symbol!(
+            self.lib,
+            b"krun_add_vsock\0",
+            unsafe extern "C" fn(u32, u32) -> i32
+        );
+        // Safety: plain integers; the engine validates the flag bits.
+        krun_ret(unsafe { f(ctx_id, tsi_flags) }, "krun_add_vsock")
+    }
+
     /// `krun_set_workdir`
     pub fn set_workdir(&self, ctx_id: u32, workdir: &str) -> Result<()> {
         let workdir_c = CString::new(workdir).context("workdir contains a NUL")?;

crates/ecrou/src/vm.rs

@@ -140,6 +140,9 @@ pub fn run(options: &RunOptions, progress: &dyn Progress) -> Result<i32> {
     for (share, gs) in &share_pairs {
         krun.add_virtiofs(ctx, &gs.tag, &share.host)?;
     }
+    // Explicit vsock with AF_INET hijacked: the implicit heuristics
+    // mode proxies fine for plain HTTP but starves TLS.
+    krun.add_vsock(ctx, 0b1)?;
     // The blob chdirs from KRUN_WORKDIR before exec; the script's cd
     // stays as the fallback path.
     if !options.workdir.is_empty() && options.workdir != "/" {