1 files changed, 18 insertions, 3 deletions
diff --git a/src/main.zig b/src/main.zig
index 60491052..92b59bc2 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -53,18 +53,33 @@ fn logFn(
 // exactly the behaviour that was here before.
 pub const panic = if (is_emscripten) std.debug.FullPanic(std.debug.defaultPanic) else std.debug.FullPanic(struct {
     fn call(msg: []const u8, ret_addr: ?usize) noreturn {
-        @import("vaxis").recover();
-        @import("crash.zig").record(msg, ret_addr);
+        // ONCE. This handler is re-entered whenever something panics while it
+        // runs, and std's own trace printer does exactly that — `defaultPanic`
+        // survives its own recursion through a private `panic_stage`, and
+        // everything up here is in front of that guard. `recover()` is not
+        // idempotent: it closes the vaxis tty and never clears the global that
+        // says there is one, so a second call double-closes, which std answers
+        // with `recoverableOsBugDetected` and an `unreachable` in a Debug
+        // build. Measured with the crash file in place: one panic left TWO
+        // records, the real message and then "reached unreachable code" from
+        // this line under it.
+        if (!recovering.swap(true, .seq_cst)) @import("vaxis").recover();
+        @import("crash.zig").record(msg);
         std.debug.defaultPanic(msg, ret_addr);
     }
 }.call);
 
+/// Whether this process has already restored its terminal — see `panic` above,
+/// and note that `debug.handleSegfault` below shares it: a SIGSEGV raised while
+/// the panic handler runs must not double-close either.
+var recovering: std.atomic.Value(bool) = .init(false);
+
 // Fatal signals (SIGSEGV/SIGILL/SIGBUS/SIGFPE) bypass the panic handler and
 // no defer/errdefer ever runs — hook std.debug's segfault path the same way
 // so the terminal is restored before the trace prints.
 pub const debug = if (is_emscripten) struct {} else struct {
     pub fn handleSegfault(addr: ?usize, name: []const u8, opt_ctx: anytype) noreturn {
-        @import("vaxis").recover();
+        if (!recovering.swap(true, .seq_cst)) @import("vaxis").recover();
         return std.debug.defaultHandleSegfault(addr, name, opt_ctx);
     }
 };