A demo recorder: --record-pad writes what --pad reads

One byte a frame, in exactly the format the player takes, so a recording
needs no conversion and there is no second format to keep in step. That
symmetry is the feature, and it makes the strongest form of the claim
testable: a recording is made OF a playback, and the bytes coming out have
to be the bytes that went in.

It exists because some inputs cannot sensibly be written by hand. Flying a
lander from one base to another is a few hundred frames of steering that
has to arrive somewhere eight cells wide, and several attempts at
authoring one got within two columns and no closer. That is a piloting
exercise rather than a test. Playing it once and keeping what happened is
the answer.

A BYTE FOR EVERY FRAME, written inside the loop that advances the
recordings rather than after it, so a machine that jumped several frames
at once still writes one for each. A recording is a timeline: one that
skipped the frames nobody looked at would play back faster than it was
flown.

What is recorded is what the DEVICE WOULD REPORT, not the live state - a
recording of a playback that wrote the live state would be a file of
noughts. And it is flushed as it goes, because a recording is usually
stopped by whoever is playing rather than by the program ending, and a
demo lost to a buffer is a demo flown twice.

Tests/replay.sh is where this and whatever follows it are checked. Twelve
scripts now.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW

Source/Emulator/machine.c

@@ -238,6 +238,15 @@ uint8_t machineStart(Machine *m, const EmulatorOptions *options, const char *pro
         padFromFile(n, pad);
     }
 
+    for (int n = 0; n < options->padRecordCount; n++) {
+        FILE *pad = fopen(options->padRecord[n], "wb");
+        if (pad == NULL) {
+            fprintf(stderr, "Error: Couldn't write pad file: %s\n", options->padRecord[n]);
+            return 0;
+        }
+        padRecordTo(n, pad);
+    }
+
     if (options->keyboard != NULL) {
         keyboardFile = fopen(options->keyboard, "rb");
         if (keyboardFile == NULL) {