test fault-on-AP and affinity; report the faulting core

fault-ap-df pins a #DF to an AP (its own IST must catch it); affinity checks a pinned task never migrates. onException now names the core, so an AP fault is attributed and shown contained. Both teeth-checked.

src/kernel/main.zig

@@ -320,21 +320,25 @@ fn kib(frames: u64) u64 {
     return frames * danos.page_size / (1024);
 }
 
-/// Report a CPU exception and halt. There's no fault recovery yet, so any
-/// exception is terminal — but it reports what and where (to every output sink,
-/// plus a POST code and a persistent breadcrumb) instead of silently resetting.
+/// Report a CPU exception and halt **this core**. There's no fault recovery yet, so
+/// the faulting core is terminal — but the fault is *contained* to it: on an
+/// application processor only that core stops, and the rest of the system keeps
+/// running (full recovery — kill the task, keep the core — is the resilience track,
+/// see docs/resilience.md). The report names the core so an AP fault is attributed,
+/// and goes to every output sink plus a POST code and a persistent breadcrumb.
 fn onException(state: *const arch.CpuState) noreturn {
     log.checkpoint(cp_exception);
+    const core = scheduler.currentCpuIndex();
     // A fault is user-facing enough to paint on screen too (via statusPrint), on
     // top of the diagnostic log.
-    statusPrint("\nCPU EXCEPTION: {s} (vector {d})\n", .{ arch.vectorName(state.vector), state.vector });
+    statusPrint("\nCPU EXCEPTION on core {d}: {s} (vector {d})\n", .{ core, arch.vectorName(state.vector), state.vector });
     statusPrint("  error code : 0x{x}\n", .{state.error_code});
     statusPrint("  RIP        : 0x{x:0>16}\n", .{state.rip});
     statusPrint("  RSP        : 0x{x:0>16}\n", .{state.rsp});
     if (state.vector == 14) statusPrint("  CR2 (addr) : 0x{x:0>16}\n", .{arch.readCr2()});
 
     var buf: [128]u8 = undefined;
-    log.recordPanic(std.fmt.bufPrint(&buf, "CPU exception {s} (vector {d}) at RIP 0x{x}", .{ arch.vectorName(state.vector), state.vector, state.rip }) catch "cpu exception");
+    log.recordPanic(std.fmt.bufPrint(&buf, "CPU exception {s} (vector {d}) on core {d} at RIP 0x{x}", .{ arch.vectorName(state.vector), state.vector, core, state.rip }) catch "cpu exception");
     arch.halt();
 }