[refactor](trx-ftx): flatten ft2/ submodules into top-level src/

Move ft2/osd.rs, ft2/bitmetrics.rs, ft2/downsample.rs, ft2/sync.rs
out of the ft2/ directory into src/ as top-level modules. Convert
ft2/mod.rs to ft2.rs. Update all imports from super:: to crate::ft2::.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: Stan Grams <sjg@haxx.space>

src/decoders/trx-ftx/src/bitmetrics.rs

@@ -13,7 +13,7 @@ use rustfft::FftPlanner;
 
 use crate::constants::{FT4_COSTAS_PATTERN, FT4_GRAY_MAP};
 
-use super::{FT2_FRAME_SYMBOLS, FT2_NSS};
+use crate::ft2::{FT2_FRAME_SYMBOLS, FT2_NSS};
 
 const N_METRICS: usize = 2 * FT2_FRAME_SYMBOLS;
 

src/decoders/trx-ftx/src/downsample.rs

@@ -14,7 +14,7 @@ use std::sync::Arc;
 use num_complex::Complex32;
 use rustfft::FftPlanner;
 
-use super::{FT2_NDOWN, FT2_SYMBOL_PERIOD_F};
+use crate::ft2::{FT2_NDOWN, FT2_SYMBOL_PERIOD_F};
 
 /// Reusable scratch buffers for frequency-domain downsampling.
 pub struct DownsampleWorkspace {

src/decoders/trx-ftx/src/ft2.rs

@@ -8,24 +8,18 @@
 //! peaks in the averaged spectrum, downsample each candidate, compute 2D sync
 //! scores, extract bit metrics, and run multi-pass LDPC + OSD decode.
 
-pub mod bitmetrics;
-pub mod downsample;
-pub mod osd;
-pub mod sync;
-
 use std::sync::Arc;
 
 use num_complex::Complex32;
 use realfft::RealFftPlanner;
 use rustfft::FftPlanner;
 
+use crate::bitmetrics::BitMetricsWorkspace;
 use crate::decode::{verify_crc_and_build_message, FtxMessage};
+use crate::downsample::{DownsampleContext, DownsampleWorkspace};
+use crate::ft2_sync::{prepare_sync_waveforms, sync2d_score, SyncWaveforms};
 use crate::protocol::*;
 
-use bitmetrics::BitMetricsWorkspace;
-use downsample::{DownsampleContext, DownsampleWorkspace};
-use sync::{prepare_sync_waveforms, sync2d_score, SyncWaveforms};
-
 // FT2 DSP constants
 pub const FT2_NDOWN: usize = 9;
 pub const FT2_NFFT1: usize = 1152;
@@ -655,7 +649,7 @@ impl Ft2Pipeline {
             let mut nharderror = -1i32;
             let mut dmin = 0.0f32;
 
-            osd::ft2_decode174_91_osd(
+            crate::osd::ft2_decode174_91_osd(
                 &mut log174,
                 FTX_LDPC_K,
                 4,

src/decoders/trx-ftx/src/ft2_sync.rs

@@ -13,7 +13,7 @@ use std::sync::OnceLock;
 
 use crate::constants::FT4_COSTAS_PATTERN;
 
-use super::{FT2_NDOWN, FT2_NSS, FT2_SYMBOL_PERIOD_F, FT2_SYNC_TWEAK_MAX, FT2_SYNC_TWEAK_MIN};
+use crate::ft2::{FT2_NDOWN, FT2_NSS, FT2_SYMBOL_PERIOD_F, FT2_SYNC_TWEAK_MAX, FT2_SYNC_TWEAK_MIN};
 
 /// Number of frequency tweak entries.
 const NUM_TWEAKS: usize = (FT2_SYNC_TWEAK_MAX - FT2_SYNC_TWEAK_MIN) as usize + 1;

src/decoders/trx-ftx/src/lib.rs

@@ -2,6 +2,8 @@
 //
 // SPDX-License-Identifier: BSD-2-Clause
 
+#[allow(clippy::needless_range_loop)]
+pub mod bitmetrics;
 pub mod callsign_hash;
 pub mod constants;
 pub mod crc;
@@ -9,15 +11,21 @@ pub mod crc;
 pub mod decode;
 mod decoder;
 #[allow(clippy::needless_range_loop)]
+pub mod downsample;
+#[allow(clippy::needless_range_loop)]
 pub mod encode;
 #[allow(dead_code, clippy::needless_range_loop, clippy::too_many_arguments)]
 pub mod ft2;
 #[allow(clippy::needless_range_loop)]
+pub mod ft2_sync;
+#[allow(clippy::needless_range_loop)]
 pub mod ldpc;
 #[allow(clippy::explicit_counter_loop, clippy::needless_range_loop)]
 pub mod message;
 #[allow(dead_code)]
 pub mod monitor;
+#[allow(dead_code, clippy::needless_range_loop, clippy::too_many_arguments)]
+pub mod osd;
 pub mod protocol;
 pub mod text;