Let the probe's clock be its proof, not disable_cpu_ep_fallback

The strict flag refused the Hexagon over the ten quantise/dequantise
nodes at the graph's edges that QNN declines by policy, which cost
microseconds. A provider that hands real work to the CPU is slower than
the CPU floor and the timing already rejects it; the tablet measured
2.3 ms on the NPU against a 29.7 ms floor.

core/dr-inference-engine/src/session.rs

@@ -7,22 +7,16 @@ use crate::{Config, Role, Rung};
 
 /// Build a session for `bytes` on `rung`.
 ///
-/// `strict` is the probe's flag: with it, a provider that would hand any
-/// node to the CPU fails the build instead, so "the session built" means
-/// "the provider took the graph" and not "the provider registered" (§4).
-pub fn build(
-    rung: Rung,
-    role: Role,
-    bytes: &[u8],
-    cfg: &Config,
-    strict: bool,
-) -> ort::Result<Session> {
+/// Not strict about the CPU: `session.disable_cpu_ep_fallback` was tried as
+/// the probe's proof that a provider took the graph, and it refuses the
+/// Hexagon over the ten quantise/dequantise nodes at the graph's edges that
+/// QNN declines by policy and that cost microseconds. The probe's proof is
+/// its clock instead (§4): a provider that hands real work to the CPU is
+/// slower than the CPU floor and rejected by the same measurement.
+pub fn build(rung: Rung, role: Role, bytes: &[u8], cfg: &Config) -> ort::Result<Session> {
     let mut b = Session::builder()?
         .with_optimization_level(GraphOptimizationLevel::Level3)?
         .with_intra_threads(threads(cfg))?;
-    if strict && rung != Rung::Cpu {
-        b = b.with_config_entry("session.disable_cpu_ep_fallback", "1")?;
-    }
     // A Hexagon session loads the compiled context when there is one and
     // compiles it from the model when there is not; the engine thread is
     // what makes the second case rare (§6).