[fix](trx-config): keep the generated example off the machine that made it

The example is generated from the config defaults, and [decode_logs].dir
defaults to the running user's cache directory.  So the file rendered
/Users/sjg/Library/Caches/trx-rs/decoders on the machine that generated it and
/root/.cache/trx-rs/decoders in CI, and the up-to-date test failed for everyone
but its author.

Pin dir to an illustrative /var/lib/trx-rs/decoders in the example config;
omitting the key still falls back to the per-user directory.  A new test asserts
the rendered example contains none of this machine's home, cache or config
directories, so the next environment-derived default cannot slip through the
same way.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SyX26FCpMQxiBoC7r5K1A7
Signed-off-by: Stan Grams <sjg@haxx.space>

src/trx-config/src/example.rs

@@ -63,7 +63,8 @@ const SECTION_COMMENTS: &[(&str, &str)] = &[
     (
         "trx-server.decoders",
         "Which decoders run.  Trimming this list saves real CPU on small boxes.\n\
-         Valid names: aprs, aprs_hf, ais, cw, ft2, ft4, ft8, lrpt, sstv, vdes, wefax, wspr.",
+         Valid names: aprs, aprs_hf, ais, cw, ft2, ft4, ft8, lrpt, sstv, vdes, wefax, wspr.\n\
+         output_dir sets where sstv/wefax/lrpt write images (default: user cache dir).",
     ),
     (
         "trx-server.pskreporter",
@@ -232,6 +233,25 @@ mod tests {
         );
     }
 
+    /// Nothing in the example may be derived from the machine that generated
+    /// it: [decode_logs].dir defaults to the running user's cache directory,
+    /// which made the generated file differ between a developer's laptop and
+    /// CI, and the up-to-date test fail for everyone but its author.
+    #[test]
+    fn test_example_has_no_machine_specific_paths() {
+        let example = combined_example();
+        for dir in [dirs::home_dir(), dirs::cache_dir(), dirs::config_dir()]
+            .into_iter()
+            .flatten()
+        {
+            let dir = dir.to_string_lossy().into_owned();
+            assert!(
+                !example.contains(&dir),
+                "the example contains this machine's {dir}; pin the value in example_config()"
+            );
+        }
+    }
+
     #[test]
     fn test_example_loads_and_validates() {
         let mut file = tempfile::NamedTempFile::new().unwrap();

src/trx-config/src/server.rs

@@ -755,7 +755,14 @@ impl ServerConfig {
             audio: AudioConfig::default(),
             pskreporter: PskReporterConfig::default(),
             aprsfi: AprsFiConfig::default(),
-            decode_logs: DecodeLogsConfig::default(),
+            decode_logs: DecodeLogsConfig {
+                // Pinned rather than defaulted: the default is derived from the
+                // running user's cache directory, which would make the generated
+                // example differ from machine to machine.  Omitting the key
+                // falls back to that per-user directory.
+                dir: "/var/lib/trx-rs/decoders".to_string(),
+                ..DecodeLogsConfig::default()
+            },
             decoders: DecodersConfig::default(),
             sdr: SdrConfig::default(),
             timeouts: TimeoutsConfig::default(),

trx-rs.toml.example

@@ -86,7 +86,7 @@ beacon_symbol_code = "-"
 # Write decodes to JSON Lines files.
 [trx-server.decode_logs]
 enabled = false
-dir = "/Users/sjg/Library/Caches/trx-rs/decoders"
+dir = "/var/lib/trx-rs/decoders"
 aprs_file = "TRXRS-APRS-%YYYY%-%MM%-%DD%.log"
 cw_file = "TRXRS-CW-%YYYY%-%MM%-%DD%.log"
 ft8_file = "TRXRS-FT8-%YYYY%-%MM%-%DD%.log"
@@ -95,6 +95,7 @@ wefax_file = "TRXRS-WEFAX-%YYYY%-%MM%-%DD%.log"
 
 # Which decoders run.  Trimming this list saves real CPU on small boxes.
 # Valid names: aprs, aprs_hf, ais, cw, ft2, ft4, ft8, lrpt, sstv, vdes, wefax, wspr.
+# output_dir sets where sstv/wefax/lrpt write images (default: user cache dir).
 [trx-server.decoders]
 enabled = [
     "aprs",