solve_global_scene: treat MP_MAXITER as calibration failure

MP_MAXITER (return code 5) means the solver exhausted its iteration
budget without converging. The current code treats this as success
(res <= 0 is false), so the unconverged — and potentially wrong —
lighthouse positions are written to disk via survive_recording and
the GSS result is accepted.

On the next launch those positions are loaded as the starting point
for calibration. If the unconverged solve is significantly wrong,
all subsequent tracking is corrupted and the only recovery is to
delete config.json.

Adding res == MP_MAXITER to the failure condition rejects unconverged
GSS solves the same way as explicit solver errors.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: 2 people

src/poser_mpfit.c

@@ -957,7 +957,10 @@ bool solve_global_scene(struct SurviveContext *ctx, MPFITData *d, PoserDataGloba
 
 	survive_get_ctx_lock(ctx);
 	survive_recording_write_matrix(ctx->recptr, 0, 5, "GSS", &R);
-	bool status_failure = res <= 0;
+	/* MP_MAXITER means the solver exhausted its iteration budget without
+	 * converging. The result is an intermediate, unconverged pose — treat it
+	 * as a failure so the bad lighthouse positions are not written to disk. */
+	bool status_failure = res <= 0 || res == MP_MAXITER;
 	FLT sensor_covariance = d->sensor_variance * d->sensor_variance;
 	FLT sensor_error = sqrtf(mpfitctx.stats.sensor_error / mpfitctx.stats.sensor_error_cnt);
 	if (status_failure || sensor_error > d->opt.max_cal_error) {