diff --git a/issues/0140-comptime-type-construction-bail-unresolved-panic.md b/issues/0140-comptime-type-construction-bail-unresolved-panic.md
index 51ed1acb..806afd25 100644
--- a/issues/0140-comptime-type-construction-bail-unresolved-panic.md
+++ b/issues/0140-comptime-type-construction-bail-unresolved-panic.md
@@ -1,5 +1,21 @@
 # 0140 — a failing comptime type construction panics ("unresolved type reached LLVM emission") instead of diagnosing the bail
 
+> **RESOLVED (2026-06-17).** Root cause exactly as the investigation prompt
+> hypothesized: `evalComptimeType` (`src/ir/lower/comptime.zig`) did
+> `interp.call(...) catch return null`, dropping the interpreter's
+> `last_bail_detail`; callers poisoned to `.unresolved` with no diagnostic, so the
+> sentinel reached LLVM emission and tripped the codegen panic (or hid behind a
+> downstream cascade). Fix: clear `Interpreter.last_bail_detail` before the call,
+> and on the `catch` emit a build-gating `.err` at the construction expression's
+> span — `"comptime type construction failed: {detail}"` (mirroring the `#run`
+> surfacing at `emit_llvm.zig:856`) — then return null (keeping the `.unresolved`
+> poison, now gated by a real message). The empty-variants repro now prints
+> `comptime type construction failed: comptime define(): enum has no variants`
+> and exits 1 (no panic); make_enum-style computed-slice failures surface their
+> root reason at the construction site instead of only the `.green` cascade.
+> Regression test:
+> [examples/1179-diagnostics-comptime-type-construction-bail.sx](../examples/1179-diagnostics-comptime-type-construction-bail.sx).
+
 ## Symptom
 
 One-line: when a comptime type construction (`declare`/`define`) bails in the
diff --git a/src/ir/lower/comptime.zig b/src/ir/lower/comptime.zig
index d709c206..35e3fed6 100644
--- a/src/ir/lower/comptime.zig
+++ b/src/ir/lower/comptime.zig
@@ -454,7 +454,25 @@ pub fn evalComptimeType(self: *Lowering, expr: *const Node) ?TypeId {
     if (self.diagnostics) |d| if (d.import_sources) |sm| interp.setSourceMap(sm);
     interp.setMintTable(&self.module.types);
 
-    const result = interp.call(func_id, &.{}) catch return null;
+    // Clear the interp's last-bail channel so a bail HERE is attributable to
+    // THIS construction (not a stale message from an earlier comptime eval).
+    interp_mod.Interpreter.last_bail_detail = null;
+    const result = interp.call(func_id, &.{}) catch |err| {
+        // A comptime type construction (declare/define, reflection) that bails
+        // must surface a build-gating diagnostic naming the reason — NOT poison
+        // to `.unresolved` silently and let that crash at LLVM emission
+        // ("unresolved type reached LLVM emission") or hide behind a downstream
+        // cascade (issue 0140). The interp's `bailDetail` already set the precise
+        // reason; mirror the `#run` path (emit_llvm.zig) and render it. Returning
+        // null keeps the `.unresolved` poison for the caller, but now the build
+        // is gated by a real message, so no unresolved type reaches emission
+        // unannounced.
+        if (self.diagnostics) |d| {
+            const detail = interp_mod.Interpreter.last_bail_detail orelse @errorName(err);
+            d.addFmt(.err, expr.span, "comptime type construction failed: {s}", .{detail});
+        }
+        return null;
+    };
     return result.asTypeId();
 }