Bootstrap hotpath from engineering spec v0.1

Commit the spec and scaffold the system it describes:

- SPEC.md: the full v0.1 engineering spec
- crates/: trust-layer Rust workspace, unit-tested
  - bench-runner: interleaved ABAB scheduling with discarded warm-ups,
    deterministic bootstrap CIs over the ratio of medians,
    CI-lower-bound accept rule, env fingerprinting, and a CLI with
    compare + A/A self-test modes (A/A verified passing end-to-end)
  - diff-test: gate outcome model, sha256 corpus pin verifier that
    refuses on mismatch, per-target equivalence policy parser
    (byte-identical default, explicit fp-tolerance opt-in)
  - ledger: append-only SQLite attempt schema with UPDATE/DELETE
    refused by triggers, anti-double-attempt query
  - report: cores-saved and dollars/yr ROI math over speedup CIs,
    pricing.toml inputs
- playbook/: classes 1-7 with preconditions, procedure, verification
  notes, and known failure modes per class
- agent/: Python package skeleton — six-tool contract and prompting
  spine, harness IPC deferred to Phase 1
- config/: accept.toml (2% threshold, 30 runs/side), pricing.toml
- targets/, corpora/, results/calibration/: layout and policy docs

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EcKPWQ3MQD4NdEHwar96u2

crates/bench-runner/src/config.rs

@@ -0,0 +1,48 @@
+//! Accept-threshold configuration, loaded from `config/accept.toml`.
+
+use serde::Deserialize;
+use std::path::Path;
+
+#[derive(Debug, Clone, Deserialize)]
+#[serde(deny_unknown_fields)]
+pub struct AcceptConfig {
+    /// CI lower bound must clear 1 + threshold (default 2%).
+    pub threshold: f64,
+    /// Measured runs per side (SPEC minimum: 30).
+    pub runs_per_side: usize,
+    /// Unmeasured warm-up runs per side, discarded.
+    pub warmup_runs: usize,
+    /// Bootstrap resample count.
+    pub bootstrap_iters: usize,
+    /// Confidence level for the ratio CI, e.g. 0.95.
+    pub confidence: f64,
+    /// PRNG seed for the bootstrap (reproducible calibration).
+    pub bootstrap_seed: u64,
+}
+
+impl Default for AcceptConfig {
+    fn default() -> Self {
+        Self {
+            threshold: 0.02,
+            runs_per_side: 30,
+            warmup_runs: 3,
+            bootstrap_iters: 10_000,
+            confidence: 0.95,
+            bootstrap_seed: 0x707E_17E5,
+        }
+    }
+}
+
+impl AcceptConfig {
+    pub fn load(path: &Path) -> anyhow::Result<Self> {
+        let raw = std::fs::read_to_string(path)?;
+        let cfg: Self = toml::from_str(&raw)?;
+        anyhow::ensure!(cfg.runs_per_side >= 2, "runs_per_side must be >= 2");
+        anyhow::ensure!(cfg.threshold > 0.0, "threshold must be positive");
+        anyhow::ensure!(
+            (0.0..1.0).contains(&cfg.confidence),
+            "confidence must be in (0, 1)"
+        );
+        Ok(cfg)
+    }
+}