Stream full-trace evidence at 100% coverage; verified at merge scale (1M)

run_all_to streams every base execution's full trace+delta to disk (no sampling);
main writes evidence/traces.tsv covering 100% of base executions. Verified
end-to-end at the real merge profile:

  merge run: 1,000,000 executions / 11,000,000 comparisons, all gates PASS, 288s
  evidence: leaves.tsv = 11,000,000 leaves; traces.tsv = 1,000,000 full traces (3.9G)
  independent attest: recomputed root a2b27c027f87788f over 11,000,000 leaves ==
    claimed; 1,000,000/1,000,000 full traces reconstructed and re-derived to
    retained leaves.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/ci_reports/src/lib.rs

@@ -24,6 +24,7 @@ use reference_runtime::{
 use runtime_under_test::{native_resolve, RuntimeUnderTest};
 use semantic_mutation::{generate_mutants, DetectionClass, MutationOutcome};
 use std::collections::HashMap;
+use std::io::Write;
 use world_model::{
     Hash, Hasher, TraceDifferenceExpectation, WorldSnapshot, HIDDEN_LANES, LANES, NUM_DOMAINS,
 };
@@ -703,6 +704,13 @@ impl CiResults {
 // ---------------------------------------------------------------------------
 
 pub fn run_all(scale: Scale) -> CiResults {
+    run_all_to(scale, None)
+}
+
+/// Like [`run_all`] but streams the FULL per-execution trace evidence (every
+/// base execution, not a sample) to `evidence_sink` as it runs, so the merge
+/// profile can retain 100% full-trace coverage without holding it in memory.
+pub fn run_all_to(scale: Scale, mut evidence_sink: Option<&mut dyn Write>) -> CiResults {
     let cfg = EngineConfig::reference();
     let rut = RuntimeUnderTest::new();
 
@@ -887,7 +895,23 @@ pub fn run_all(scale: Scale) -> CiResults {
                 equiv_failures.push(format!("case {} (base) reference != runtime_under_test", i));
             }
             merkle_leaves.push(r.replay.hash());
-            // Retain a sample of FULL traces as independent evidence (finding 4).
+            // Full-trace evidence (finding 4): stream EVERY base execution's full
+            // trace + delta to the sink (100% coverage, no sampling). A small
+            // in-memory sample is also kept for non-streaming callers/tests.
+            if let Some(w) = evidence_sink.as_deref_mut() {
+                let _ = writeln!(
+                    w,
+                    "{:016x} {:016x} {:016x} {:016x} {:016x} {:016x}\t{}\t{}",
+                    r.replay.world_seed,
+                    r.replay.program_seed,
+                    r.replay.contract_seed,
+                    r.replay.perturbation_seed,
+                    r.replay.future_hash.0,
+                    r.replay.hash().0,
+                    r.trace.serialize(),
+                    r.delta.serialize(),
+                );
+            }
             if trace_evidence.len() < TRACE_EVIDENCE_SAMPLE {
                 trace_evidence.push(TraceEvidence {
                     replay: r.replay,

crates/ci_reports/src/main.rs

@@ -4,7 +4,7 @@
 //! to executed work, and exits nonzero if any gate fails.
 
 use ci_reports::json::Json;
-use ci_reports::{run_all, CiResults, Profile, Scale};
+use ci_reports::{run_all_to, CiResults, Profile, Scale};
 use std::fs;
 use std::io::Write;
 use std::path::Path;
@@ -59,28 +59,9 @@ fn write_evidence(dir: &Path, r: &CiResults) {
         r.provenance.engines_agree,
     );
     fs::write(ev.join("claims.tsv"), claims).expect("write claims");
-
-    // Full-trace evidence (finding 4): each line is
-    //   ws ps cs prs future leaf <TAB> <full trace> <TAB> <full delta>
-    // The attestor reconstructs the trace + delta, recomputes the canonical
-    // trace hash and the replay-record leaf, and checks the leaf is among the
-    // retained leaves. This is the full trace, not a summary.
-    let mut traces = String::from("# full-trace evidence: header<TAB>trace<TAB>delta\n");
-    for ev_rec in &r.trace_evidence {
-        let rr = &ev_rec.replay;
-        traces.push_str(&format!(
-            "{:016x} {:016x} {:016x} {:016x} {:016x} {:016x}\t{}\t{}\n",
-            rr.world_seed,
-            rr.program_seed,
-            rr.contract_seed,
-            rr.perturbation_seed,
-            rr.future_hash.0,
-            rr.hash().0,
-            ev_rec.trace.serialize(),
-            ev_rec.delta.serialize(),
-        ));
-    }
-    fs::write(ev.join("traces.tsv"), traces).expect("write traces");
+    // Note: evidence/traces.tsv (the FULL per-execution trace corpus) is streamed
+    // during the run in main(), covering 100% of base executions — not written
+    // here from a capped sample.
 }
 
 fn build_reports(dir: &Path, r: &CiResults) {
@@ -632,7 +613,17 @@ fn main() {
     }
     let merge = scale.profile == Profile::Merge;
     let start = Instant::now();
-    let results = run_all(scale);
+    // Stream full-trace evidence for 100% of base executions straight to disk.
+    let ev_dir = dir.join("evidence");
+    fs::create_dir_all(&ev_dir).expect("create evidence dir");
+    let traces_path = ev_dir.join("traces.tsv");
+    let mut traces_w = std::io::BufWriter::new(fs::File::create(&traces_path).expect("create traces"));
+    traces_w
+        .write_all(b"# full-trace evidence (100% of base executions): header<TAB>trace<TAB>delta\n")
+        .expect("write traces header");
+    let results = run_all_to(scale, Some(&mut traces_w));
+    traces_w.flush().expect("flush traces");
+    drop(traces_w);
     let elapsed = start.elapsed();
 
     build_reports(dir, &results);