The pod answers the Play handshake, and declines it

`--sweep` against a recovered pod, and two findings worth more than the
thing it was built to test.

**The v2 speaks the documented Play handshake.** Sent `RideOn 01 02` plus
a raw 64-byte key — §3.5's format, no protobuf envelope, the one shape we
had never tried because the offer's protobuf framing made it look
irrelevant — and the pod replied `RideOn 02 03` followed by 64 **zero**
bytes. That is the Play reply shape with the key zeroed: it understood
the question and refused to answer it. The four protobuf variants all
drew `0x3e {1: 255, 2: 5}`.

**And the stream then went to all-zero frames**, button frames included,
at their usual rate. We can put the pod into a state where it emits
nothing but zeros. It recovers by itself.

Also recorded: the stuck state is not permanent. The pod that opened
three sessions already past the cliff, with the `+` paddle bit pinned in
its hello, came back clean — `flag=0`, idle bitmask, `−` paddle
reporting. The unit is sealed and was never opened.

The sweep's attribution is not sound and the commit does not pretend
otherwise: five writes inside six seconds, every reply in one burst at
+11.37 s. `--variant <name>` now sends exactly one frame per connection,
which is the only way to learn which one does what. Zero frames are
counted and named rather than scrolling past as `other`.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

crates/probe/src/cli.rs

@@ -109,6 +109,8 @@ pub enum Command {
         /// Needs no button presses, so it works on a pod that has stopped
         /// reporting them.
         sweep: bool,
+        /// Send exactly one named variant, so its effect is unambiguous.
+        variant: Option<String>,
     },
     /// Phase 3 / TASK-0: exercise Zwift's custom service on whatever advertises
     /// it — a Click, or the trainer itself.
@@ -147,6 +149,7 @@ pub fn parse<I: IntoIterator<Item = String>>(argv: I) -> Result<Args> {
     let mut name: Option<String> = None;
     let mut candidate: Option<String> = None;
     let mut sweep = false;
+    let mut variant: Option<String> = None;
     let mut help = false;
     let mut positional: Vec<String> = Vec::new();
 
@@ -171,6 +174,14 @@ pub fn parse<I: IntoIterator<Item = String>>(argv: I) -> Result<Args> {
                 );
             }
             "--sweep" => sweep = true,
+            "--variant" => {
+                i += 1;
+                variant = Some(
+                    args.get(i)
+                        .ok_or_else(|| anyhow!("--variant needs a value"))?
+                        .clone(),
+                );
+            }
             "--candidate" => {
                 i += 1;
                 candidate = Some(
@@ -253,6 +264,7 @@ pub fn parse<I: IntoIterator<Item = String>>(argv: I) -> Result<Args> {
             duration: Duration::from_secs(secs.unwrap_or(150)),
             candidate: candidate.clone(),
             sweep,
+            variant: variant.clone(),
         },
         "zwift" => Command::Zwift {
             device: device(&positional, 1)?,

crates/probe/src/commands.rs

@@ -976,6 +976,7 @@ pub async fn unlock_cmd(
     duration: Duration,
     candidate: Option<&str>,
     sweep: bool,
+    variant: Option<&str>,
     scan_timeout: Duration,
 ) -> Result<()> {
     use crate::unlock;
@@ -1001,6 +1002,19 @@ pub async fn unlock_cmd(
         ),
     }
 
+    let single = match variant {
+        None => None,
+        Some(name) => Some(unlock::variant(name).ok_or_else(|| {
+            anyhow::anyhow!(
+                "unknown variant {name:?}. Known: {}",
+                unlock::VARIANTS.iter().map(|v| v.name).collect::<Vec<_>>().join(", ")
+            )
+        })?),
+    };
+    if let Some(v) = single {
+        println!("Sending exactly one frame this run: {}\n", v.name);
+    }
+
     let peripheral = connect(device, scan_timeout).await?;
     if let Some(d) = scan::describe(&peripheral).await {
         println!("Connected to {} ({})\n", d.address, d.label());
@@ -1044,6 +1058,7 @@ pub async fn unlock_cmd(
     // measured against — better than a constant, because the pod says so.
     let mut sent: Vec<&'static str> = Vec::new();
     let mut responses: Vec<(&'static str, unlock::Response)> = Vec::new();
+    let mut zeros: u64 = 0;
     let mut last_mask: Option<u32> = None;
     // When the pod flipped its status flag, which is the cliff this run is
     // measured against — better than a constant, because the pod says so.
@@ -1084,7 +1099,23 @@ pub async fn unlock_cmd(
                         ),
                         Err(e) => println!("           !! {e}"),
                     }
-                    if sweep {
+                    if let Some(one) = single {
+                        // One write per connection. The sweep's replies came
+                        // back in a single burst six seconds after the first
+                        // write, so "attributed to the last thing sent" was a
+                        // label, not a measurement. This is how you learn which
+                        // frame does what.
+                        let frame = (one.build)(&local, &offer);
+                        println!("\n  -> {:<20} {}", one.name, hex(&frame));
+                        println!("     {}\n", one.why);
+                        match write_frame(&peripheral, &sync_rx, &frame).await {
+                            Ok(()) => {
+                                answered += 1;
+                                sent.push(one.name);
+                            }
+                            Err(e) => println!("     !! could not send: {e}"),
+                        }
+                    } else if sweep {
                         // One connection, every variant, because the pod hands
                         // back a reason for each. Spaced so a late reply cannot
                         // be attributed to the next thing we sent.
@@ -1146,6 +1177,17 @@ pub async fn unlock_cmd(
                     continue;
                 }
 
+                if !n.value.is_empty() && n.value.iter().all(|b| *b == 0) {
+                    zeros += 1;
+                    if zeros == 1 {
+                        println!(
+                            "[{at:7.2}s] ZEROS      the stream has gone to all-zero frames \
+                             — counting from here"
+                        );
+                    }
+                    continue;
+                }
+
                 if button_mask(&n.value).is_none()
                     && unlock::parse_key_offer(&n.value).is_none()
                     && unlock::parse_status(&n.value).is_none()
@@ -1190,6 +1232,9 @@ pub async fn unlock_cmd(
         _ => println!("  cliff:             never flipped"),
     }
     println!("  key offers seen:   {offers}");
+    if zeros > 0 {
+        println!("  all-zero frames:   {zeros}  <- the stream stopped carrying data");
+    }
     println!("  answered:          {answered}");
     println!(
         "  paddle edges:      {} (last at {})",

crates/probe/src/main.rs

@@ -60,8 +60,17 @@ async fn main() -> Result<()> {
             duration,
             candidate,
             sweep,
+            variant,
         } => {
-            commands::unlock_cmd(&device, duration, candidate.as_deref(), sweep, SCAN_TIMEOUT).await
+            commands::unlock_cmd(
+                &device,
+                duration,
+                candidate.as_deref(),
+                sweep,
+                variant.as_deref(),
+                SCAN_TIMEOUT,
+            )
+            .await
         }
         cli::Command::Zwift {
             device,

crates/probe/src/unlock.rs

@@ -87,6 +87,10 @@ pub struct Variant {
 /// writes to the D100 because it puts resistance under a rider; a pod has no
 /// actuator, and the worst it can do is ignore us. The OAD characteristics stay
 /// untouched — those *can* brick it, and it is sealed.
+pub fn variant(name: &str) -> Option<&'static Variant> {
+    VARIANTS.iter().find(|v| v.name == name)
+}
+
 pub const VARIANTS: &[Variant] = &[
     Variant {
         name: "compressed+ours",