fix(repl): the bring-up build's prompt waits for a line instead of answering itself without end

Built with EMERGENCY_CONSOLE_ENABLED=1 and booted with no identity logged
in, the prompt printed "ok>  ok" without end, 1.4 million times in 200
seconds (logs/20261013-210442).  sk_console_readline() gave up at once
whenever no identity was present.  The production build answers that by
going silent until a login; the bring-up build, which needs no login,
took it as an empty line and asked again.  The give-up is now the
production build's only.

Found rehearsing boards/BRINGUP.md; it predates the console change of
c9519173 (the image built from the commit before that did the same).

The riscv64 bring-up build, no thumbdrive, three lines typed
(logs/20261013-235129): one prompt that waits, and 3, 56 and 81.
Acceptance of the production build, one QEMU at a time: amd64
(-235255), aarch64 (-235411), riscv64 (-235620) to the zuse prompt, no
unknown word, hash 0x08873e0f44b7cb2a on all three.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

kernel/src/repl.c

@@ -1283,9 +1283,16 @@ int sk_console_readline(char* buf, int size, VM* active_vm, int reanchor_prompt)
              * before this fix (a bare, unauthenticated prompt stayed on
              * screen after every logout for the rest of the boot). n == 0
              * only: never abandon a line the user is actively typing. */
+#if !EMERGENCY_CONSOLE_ENABLED
             if (reanchor_prompt && n == 0 && !sk_console_identity_present()) {
                 return -1;
             }
+#endif
+            /* Not in the bring-up build (EMERGENCY_CONSOLE_ENABLED): its prompt
+             * needs no login, and sk_repl_run() takes this return as an empty
+             * line there -- with no identity attached the prompt answered " ok"
+             * and asked again without end, 1.4 million times in 200 seconds
+             * (found 2026-10-13 rehearsing boards/BRINGUP.md; logs/20261013-210442). */
 
             if (reanchor_prompt && n == 0 &&
                 console_tx_count() != prompt_tx_mark)