diff --git a/neurosploit-rs/crates/harness/src/lib.rs b/neurosploit-rs/crates/harness/src/lib.rs
index 192ead6..3d02700 100644
--- a/neurosploit-rs/crates/harness/src/lib.rs
+++ b/neurosploit-rs/crates/harness/src/lib.rs
@@ -20,6 +20,7 @@ pub mod models;
 pub mod pipeline;
 pub mod pool;
 pub mod probe;
+pub mod replay;
 pub mod report;
 pub mod rl;
 pub mod scope;
@@ -36,6 +37,7 @@ pub use pipeline::run;
 pub use knowledge_graph::{EdgeKind, KnowledgeGraph, NodeKind};
 pub use memory::{Memory, Query as MemoryQuery, Tier as MemoryTier};
 pub use pool::{ModelPool, Task};
+pub use replay::{ReplayEngine, ReqSpec};
 pub use scope::{Action as ScopeAction, Decision as ScopeDecision, ScopePolicy};
 pub use types::{Finding, RunConfig};
 pub use validation::{judge as judge_finding, CweValidator, Evidence, Verdict};
diff --git a/neurosploit-rs/crates/harness/src/probe.rs b/neurosploit-rs/crates/harness/src/probe.rs
index f116b4a..9e6492b 100644
--- a/neurosploit-rs/crates/harness/src/probe.rs
+++ b/neurosploit-rs/crates/harness/src/probe.rs
@@ -91,6 +91,14 @@ pub struct Probe {
     pub notes: Vec<String>,
 }
 
+/// The harness's HTTP client: identifying User-Agent, proxy honoured, and
+/// invalid certificates tolerated (test targets rarely have valid ones).
+/// Shared with `crate::replay` so every request the harness itself makes is
+/// shaped the same way and is attributable to NeuroSploit.
+pub fn http_client() -> reqwest::Client {
+    client()
+}
+
 fn client() -> reqwest::Client {
     let ua = std::env::var("NEUROSPLOIT_UA").ok().filter(|v| !v.trim().is_empty())
         .unwrap_or_else(crate::pipeline::default_user_agent);
diff --git a/neurosploit-rs/crates/harness/src/replay.rs b/neurosploit-rs/crates/harness/src/replay.rs
new file mode 100644
index 0000000..08b3704
--- /dev/null
+++ b/neurosploit-rs/crates/harness/src/replay.rs
@@ -0,0 +1,357 @@
+//! Replay engine — the harness re-runs an interaction itself.
+//!
+//! The validators in [`crate::validation`] decide from recorded artifacts, and
+//! the weakest link in that chain is who recorded them. An agent reporting "the
+//! payload returned a 500" is still an agent's account of what happened. Replay
+//! closes that gap for the part that matters most in practice: **reproducibility**.
+//! SQL injection is confirmed by a difference that repeats, and a difference
+//! observed once on a dynamic page is the single most common false positive in
+//! the class.
+//!
+//! So the harness sends the request again — itself, through its own client,
+//! with its own scope guard in front of it — and keeps what came back. What it
+//! produces is evidence about the target, not a description of evidence.
+//!
+//! Three properties this module is built around:
+//!
+//! - **Every request passes the guard.** [`crate::scope::ScopePolicy::check_request`]
+//!   runs before the socket is opened, so replay cannot be the thing that
+//!   wanders off-scope while trying to verify a finding.
+//! - **Replay never mutates.** A finding proven with DELETE is not re-proven by
+//!   deleting the record again. Non-idempotent verbs are refused unless the
+//!   operator explicitly allowed destructive actions, and even then repeats are
+//!   capped at one.
+//! - **Bodies are truncated.** Evidence is stored with the run and shipped in
+//!   the report; a 40MB response is not evidence, it is a liability.
+
+use crate::scope::{Action, ScopePolicy};
+use crate::validation::{Evidence, Exchange};
+use std::collections::BTreeMap;
+use std::time::{Duration, Instant};
+
+/// A request the engine can perform.
+#[derive(Debug, Clone, Default)]
+pub struct ReqSpec {
+    pub method: String,
+    pub url: String,
+    pub headers: BTreeMap<String, String>,
+    pub body: String,
+    /// Label for the identity these credentials belong to ("userA", "anonymous").
+    pub identity: String,
+}
+
+impl ReqSpec {
+    pub fn get(url: &str) -> ReqSpec {
+        ReqSpec { method: "GET".into(), url: url.to_string(), ..Default::default() }
+    }
+    pub fn with_header(mut self, k: &str, v: &str) -> Self {
+        self.headers.insert(k.to_string(), v.to_string());
+        self
+    }
+    pub fn as_identity(mut self, who: &str) -> Self {
+        self.identity = who.to_string();
+        self
+    }
+    /// Verbs that change state. Replay refuses these by default: re-running a
+    /// destructive request to "confirm" it means doing the damage twice.
+    pub fn is_mutating(&self) -> bool {
+        !matches!(self.method.to_uppercase().as_str(), "GET" | "HEAD" | "OPTIONS")
+    }
+}
+
+/// Response bodies above this are truncated. Big enough for a page or an API
+/// payload, small enough that a run's evidence stays readable and shippable.
+pub const BODY_CAP: usize = 96 * 1024;
+
+/// Why a replay could not happen. Kept as data rather than logged and dropped,
+/// because "we could not verify this" belongs in the finding's review reason.
+#[derive(Debug, Clone)]
+pub enum ReplayError {
+    OutOfScope(String),
+    Mutating(String),
+    Transport(String),
+    NoRequest,
+}
+
+impl std::fmt::Display for ReplayError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            ReplayError::OutOfScope(r) => write!(f, "scope guard refused the replay: {r}"),
+            ReplayError::Mutating(m) => write!(f, "{m} is state-changing — not replayed"),
+            ReplayError::Transport(e) => write!(f, "replay failed: {e}"),
+            ReplayError::NoRequest => write!(f, "nothing recorded to replay"),
+        }
+    }
+}
+
+pub struct ReplayEngine {
+    client: reqwest::Client,
+    policy: ScopePolicy,
+    /// Pause between repeats so verification does not look like a flood.
+    pace: Duration,
+}
+
+impl ReplayEngine {
+    pub fn new(policy: ScopePolicy) -> Self {
+        ReplayEngine { client: crate::probe::http_client(), policy, pace: Duration::from_millis(350) }
+    }
+
+    pub fn with_pace(mut self, pace: Duration) -> Self {
+        self.pace = pace;
+        self
+    }
+
+    /// Perform one request and record it.
+    pub async fn send(&self, req: &ReqSpec) -> Result<Exchange, ReplayError> {
+        if req.url.trim().is_empty() {
+            return Err(ReplayError::NoRequest);
+        }
+        let decision = self.policy.check_request(&req.url, &req.method, &req.body);
+        if !decision.allowed() {
+            return Err(ReplayError::OutOfScope(decision.reason().to_string()));
+        }
+        if req.is_mutating() && !self.policy.soft.allow_destructive_methods {
+            return Err(ReplayError::Mutating(req.method.to_uppercase()));
+        }
+
+        let method = reqwest::Method::from_bytes(req.method.to_uppercase().as_bytes())
+            .unwrap_or(reqwest::Method::GET);
+        let mut rb = self.client.request(method, &req.url);
+        for (k, v) in &req.headers {
+            rb = rb.header(k.as_str(), v.as_str());
+        }
+        if !req.body.is_empty() {
+            rb = rb.body(req.body.clone());
+        }
+
+        let started = Instant::now();
+        let resp = rb.send().await.map_err(|e| ReplayError::Transport(e.to_string()))?;
+        let status = resp.status().as_u16();
+        let mut headers = BTreeMap::new();
+        for (k, v) in resp.headers().iter() {
+            // Multi-value headers (notably Set-Cookie) are joined rather than
+            // dropped: the cookie validators read flags out of the whole string.
+            let key = k.as_str().to_lowercase();
+            let val = v.to_str().unwrap_or("").to_string();
+            headers
+                .entry(key)
+                .and_modify(|prev: &mut String| {
+                    prev.push_str("; ");
+                    prev.push_str(&val);
+                })
+                .or_insert(val);
+        }
+        let content_type = headers.get("content-type").cloned().unwrap_or_default();
+        let body = resp.text().await.unwrap_or_default();
+        let elapsed_ms = started.elapsed().as_millis() as u64;
+
+        Ok(Exchange {
+            method: req.method.to_uppercase(),
+            url: req.url.clone(),
+            status,
+            body: truncate(&body, BODY_CAP),
+            content_type,
+            elapsed_ms,
+            identity: req.identity.clone(),
+            headers,
+            request_headers: req.headers.clone(),
+        })
+    }
+
+    /// Send the same request `n` extra times, pacing between them.
+    ///
+    /// This is what a reproducibility rule actually needs: the SQLi validator
+    /// asks for the difference to hold across repeats, and only the harness can
+    /// honestly produce them.
+    pub async fn repeat(&self, req: &ReqSpec, n: usize) -> (Vec<Exchange>, Vec<String>) {
+        let mut out = Vec::new();
+        let mut notes = Vec::new();
+        if req.is_mutating() {
+            notes.push(format!("{} not repeated — replaying a state-changing request would act twice", req.method.to_uppercase()));
+            return (out, notes);
+        }
+        for i in 0..n {
+            if i > 0 {
+                tokio::time::sleep(self.pace).await;
+            }
+            match self.send(req).await {
+                Ok(x) => out.push(x),
+                Err(e) => {
+                    notes.push(e.to_string());
+                    break;
+                }
+            }
+        }
+        (out, notes)
+    }
+
+    /// Fill in what a finding's evidence is missing, without inventing any of it.
+    ///
+    /// Only the repeats are produced here. A baseline cannot be derived from an
+    /// attack request in general — removing "the payload" from an arbitrary URL
+    /// is guesswork, and a guessed baseline would silently decide the verdict.
+    /// When the agent recorded one, it is re-sent so both sides of the
+    /// comparison come from the same moment in the target's life.
+    pub async fn enrich(&self, ev: &mut Evidence, want_repeats: usize) -> Vec<String> {
+        let mut notes = Vec::new();
+        let Some(attack) = ev.attack.clone() else {
+            notes.push("no attack request recorded — nothing to replay".into());
+            return notes;
+        };
+        let req = spec_of(&attack);
+        if ev.repeats.len() < want_repeats {
+            let need = want_repeats - ev.repeats.len();
+            let (mut got, mut n) = self.repeat(&req, need).await;
+            ev.repeats.append(&mut got);
+            notes.append(&mut n);
+        }
+        if let Some(base) = ev.baseline.clone() {
+            // Re-measure the baseline too: comparing a fresh attack against a
+            // baseline captured an hour ago attributes ordinary drift (a new
+            // banner, a rotated token) to the payload.
+            match self.send(&spec_of(&base)).await {
+                Ok(fresh) => ev.baseline = Some(fresh),
+                Err(e) => notes.push(format!("baseline not re-measured: {e}")),
+            }
+        }
+        ev.notes.extend(notes.iter().cloned());
+        notes
+    }
+
+    /// Request the same resource as two identities — the evidence an access
+    /// control rule needs, produced by the harness rather than described.
+    pub async fn identity_pair(&self, url: &str, a: (&str, &str), b: (&str, &str)) -> (Option<Exchange>, Option<Exchange>, Vec<String>) {
+        let mut notes = Vec::new();
+        let mk = |(who, auth): (&str, &str)| {
+            let mut r = ReqSpec::get(url).as_identity(who);
+            if !auth.is_empty() {
+                let (k, v) = auth.split_once(':').unwrap_or(("Authorization", auth));
+                r = r.with_header(k.trim(), v.trim());
+            }
+            r
+        };
+        let ra = match self.send(&mk(a)).await {
+            Ok(x) => Some(x),
+            Err(e) => {
+                notes.push(format!("identity '{}' request failed: {e}", a.0));
+                None
+            }
+        };
+        tokio::time::sleep(self.pace).await;
+        let rb = match self.send(&mk(b)).await {
+            Ok(x) => Some(x),
+            Err(e) => {
+                notes.push(format!("identity '{}' request failed: {e}", b.0));
+                None
+            }
+        };
+        (ra, rb, notes)
+    }
+}
+
+/// Rebuild a request spec from a recorded exchange.
+pub fn spec_of(x: &Exchange) -> ReqSpec {
+    ReqSpec {
+        method: if x.method.is_empty() { "GET".into() } else { x.method.clone() },
+        url: x.url.clone(),
+        headers: x.request_headers.clone(),
+        body: String::new(),
+        identity: x.identity.clone(),
+    }
+}
+
+fn truncate(s: &str, cap: usize) -> String {
+    if s.len() <= cap {
+        return s.to_string();
+    }
+    // Cut on a character boundary, then say so — a silently clipped body would
+    // make a length differential meaningless.
+    let mut end = cap;
+    while end > 0 && !s.is_char_boundary(end) {
+        end -= 1;
+    }
+    format!("{}\n…[truncated at {cap} bytes by the replay engine]", &s[..end])
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn policy() -> ScopePolicy {
+        let mut p = ScopePolicy::for_target("https://app.example.com/");
+        p.soft.max_requests_per_minute = 0;
+        p
+    }
+
+    #[tokio::test]
+    async fn a_replay_outside_scope_never_opens_a_socket() {
+        let engine = ReplayEngine::new(policy());
+        // other.test resolves nowhere; if the guard let it through this would
+        // fail with a transport error instead, which is the distinction.
+        let err = engine.send(&ReqSpec::get("https://other.test/secret")).await.unwrap_err();
+        match err {
+            ReplayError::OutOfScope(r) => assert!(r.contains("outside the authorized scope"), "{r}"),
+            e => panic!("expected a scope refusal, got {e}"),
+        }
+    }
+
+    #[tokio::test]
+    async fn a_destructive_verb_is_not_replayed_by_default() {
+        let engine = ReplayEngine::new(policy());
+        let req = ReqSpec { method: "DELETE".into(), url: "https://app.example.com/orders/1".into(), ..Default::default() };
+        match engine.send(&req).await.unwrap_err() {
+            // The scope guard gets there first, which is the stronger refusal.
+            ReplayError::OutOfScope(r) => assert!(r.contains("destructive"), "{r}"),
+            ReplayError::Mutating(m) => assert_eq!(m, "DELETE"),
+            e => panic!("a DELETE must not be replayed: {e}"),
+        }
+    }
+
+    #[tokio::test]
+    async fn repeats_are_refused_for_state_changing_requests() {
+        let engine = ReplayEngine::new(policy());
+        let req = ReqSpec { method: "POST".into(), url: "https://app.example.com/x".into(), ..Default::default() };
+        let (got, notes) = engine.repeat(&req, 3).await;
+        assert!(got.is_empty());
+        assert!(notes[0].contains("would act twice"), "{:?}", notes);
+    }
+
+    #[tokio::test]
+    async fn enrich_reports_when_there_is_nothing_to_replay() {
+        let engine = ReplayEngine::new(policy());
+        let mut ev = Evidence::default();
+        let notes = engine.enrich(&mut ev, 2).await;
+        assert!(notes[0].contains("nothing to replay"), "{:?}", notes);
+        assert!(ev.repeats.is_empty(), "the engine must not fabricate repeats");
+    }
+
+    #[test]
+    fn a_truncated_body_says_that_it_was_truncated() {
+        let big = "a".repeat(BODY_CAP + 500);
+        let t = truncate(&big, BODY_CAP);
+        assert!(t.len() < big.len());
+        assert!(t.contains("truncated"), "a silently clipped body makes a length diff meaningless");
+        // Multi-byte safety: cutting mid-character would panic on slicing.
+        let multi = "é".repeat(BODY_CAP);
+        assert!(!truncate(&multi, BODY_CAP - 1).is_empty());
+    }
+
+    #[test]
+    fn a_spec_rebuilt_from_an_exchange_keeps_identity_and_request_headers() {
+        let mut x = Exchange { method: "GET".into(), url: "https://app.example.com/a".into(), identity: "userB".into(), ..Default::default() };
+        x.request_headers.insert("Authorization".into(), "Bearer t".into());
+        let spec = spec_of(&x);
+        assert_eq!(spec.identity, "userB");
+        assert_eq!(spec.headers.get("Authorization").map(String::as_str), Some("Bearer t"));
+    }
+
+    #[test]
+    fn mutating_verbs_are_classified_correctly() {
+        for m in ["POST", "PUT", "PATCH", "DELETE"] {
+            assert!(ReqSpec { method: m.into(), ..Default::default() }.is_mutating(), "{m}");
+        }
+        for m in ["GET", "HEAD", "OPTIONS", "get"] {
+            assert!(!ReqSpec { method: m.into(), ..Default::default() }.is_mutating(), "{m}");
+        }
+    }
+}