diff --git a/crates/gateway/src/v1/iterate.rs b/crates/gateway/src/v1/iterate.rs
new file mode 100644
index 0000000..49a3ba6
--- /dev/null
+++ b/crates/gateway/src/v1/iterate.rs
@@ -0,0 +1,313 @@
+//! /v1/iterate — the Phase 43 PRD's "generate → validate → correct → retry" loop.
+//!
+//! Closes the "0→85% with iteration" thesis structurally. A caller
+//! posts a prompt + artifact kind + validation context; the gateway:
+//!   1. Generates a JSON artifact via /v1/chat (any provider/model)
+//!   2. Extracts the JSON object from the model output
+//!   3. Validates via /v1/validate (FillValidator / EmailValidator /
+//!      PlaybookValidator with the shared WorkerLookup)
+//!   4. On ValidationError, appends the error to the prompt and
+//!      retries up to `max_iterations` (default 3)
+//!   5. Returns the accepted artifact + Report on success, OR the
+//!      attempt history + final error on max-iter exhaustion
+//!
+//! Internal calls go via HTTP loopback to localhost:gateway_port so
+//! the same /v1/usage tracking and Langfuse traces apply. A small
+//! latency cost (~1-3ms per loopback hop) for clean separation of
+//! concerns and observability.
+//!
+//! 2026-04-27 Phase 43 v3 part 3: this endpoint makes the iteration
+//! loop a first-class lakehouse capability rather than a per-caller
+//! re-implementation. Staffing executors, agent loops, and future
+//! validators all reach the same code path.
+
+use axum::{extract::State, http::StatusCode, response::IntoResponse, Json};
+use serde::{Deserialize, Serialize};
+
+const DEFAULT_MAX_ITERATIONS: u32 = 3;
+const LOOPBACK_TIMEOUT_SECS: u64 = 240;
+
+#[derive(Deserialize)]
+pub struct IterateRequest {
+    /// "fill" | "email" | "playbook" — picks which validator runs.
+    pub kind: String,
+    /// The prompt to seed generation. Validation errors from prior
+    /// attempts are appended on retry.
+    pub prompt: String,
+    /// Provider/model passed through to /v1/chat. e.g. "ollama_cloud"
+    /// + "kimi-k2.6", or "opencode" + "claude-haiku-4-5".
+    pub provider: String,
+    pub model: String,
+    /// Optional system prompt — sent to /v1/chat as the system message.
+    #[serde(default)]
+    pub system: Option<String>,
+    /// Validation context (target_count, city, state, role, client_id
+    /// for fills; candidate_id for emails). Forwarded to /v1/validate.
+    #[serde(default)]
+    pub context: Option<serde_json::Value>,
+    /// Cap on iteration count. Defaults to 3 per the Phase 43 PRD.
+    #[serde(default)]
+    pub max_iterations: Option<u32>,
+    /// Forwarded to /v1/chat. Defaults to 0.2 if unset.
+    #[serde(default)]
+    pub temperature: Option<f64>,
+    /// Forwarded to /v1/chat. Defaults to 4096 if unset.
+    #[serde(default)]
+    pub max_tokens: Option<u32>,
+}
+
+#[derive(Serialize)]
+pub struct IterateAttempt {
+    pub iteration: u32,
+    pub raw: String,
+    pub status: AttemptStatus,
+}
+
+#[derive(Serialize)]
+#[serde(tag = "kind", rename_all = "snake_case")]
+pub enum AttemptStatus {
+    /// Model output didn't contain extractable JSON.
+    NoJson,
+    /// JSON extracted but failed validation; carries the error.
+    ValidationFailed { error: serde_json::Value },
+    /// Validation passed (last attempt's terminal status).
+    Accepted,
+}
+
+#[derive(Serialize)]
+pub struct IterateResponse {
+    pub artifact: serde_json::Value,
+    pub validation: serde_json::Value,
+    pub iterations: u32,
+    pub history: Vec<IterateAttempt>,
+}
+
+#[derive(Serialize)]
+pub struct IterateFailure {
+    pub error: String,
+    pub iterations: u32,
+    pub history: Vec<IterateAttempt>,
+}
+
+pub async fn iterate(
+    State(state): State<super::V1State>,
+    Json(req): Json<IterateRequest>,
+) -> impl IntoResponse {
+    let max_iter = req.max_iterations.unwrap_or(DEFAULT_MAX_ITERATIONS).max(1);
+    let temperature = req.temperature.unwrap_or(0.2);
+    let max_tokens = req.max_tokens.unwrap_or(4096);
+    let mut history: Vec<IterateAttempt> = Vec::with_capacity(max_iter as usize);
+    let mut current_prompt = req.prompt.clone();
+
+    let client = match reqwest::Client::builder()
+        .timeout(std::time::Duration::from_secs(LOOPBACK_TIMEOUT_SECS))
+        .build() {
+        Ok(c) => c,
+        Err(e) => return (StatusCode::INTERNAL_SERVER_ERROR, format!("client build: {e}")).into_response(),
+    };
+    // Self-loopback to the gateway port. Carries gateway internal
+    // calls through /v1/chat + /v1/validate so /v1/usage tracks them.
+    let gateway = "http://127.0.0.1:3100";
+
+    for iteration in 0..max_iter {
+        // ── Generate ──
+        let mut messages = Vec::with_capacity(2);
+        if let Some(sys) = &req.system {
+            messages.push(serde_json::json!({"role": "system", "content": sys}));
+        }
+        messages.push(serde_json::json!({"role": "user", "content": current_prompt}));
+        let chat_body = serde_json::json!({
+            "messages": messages,
+            "provider": req.provider,
+            "model": req.model,
+            "temperature": temperature,
+            "max_tokens": max_tokens,
+        });
+        let raw = match call_chat(&client, gateway, &chat_body).await {
+            Ok(r) => r,
+            Err(e) => return (StatusCode::BAD_GATEWAY, format!("/v1/chat hop failed at iter {iteration}: {e}")).into_response(),
+        };
+
+        // ── Extract JSON ──
+        let artifact = match extract_json(&raw) {
+            Some(a) => a,
+            None => {
+                history.push(IterateAttempt {
+                    iteration,
+                    raw: raw.chars().take(2000).collect(),
+                    status: AttemptStatus::NoJson,
+                });
+                current_prompt = format!(
+                    "{}\n\nYour previous attempt did not contain a JSON object. Reply with ONLY a valid JSON object matching the requested artifact shape.",
+                    req.prompt,
+                );
+                continue;
+            }
+        };
+
+        // ── Validate ──
+        let validate_body = serde_json::json!({
+            "kind": req.kind,
+            "artifact": artifact,
+            "context": req.context.clone().unwrap_or(serde_json::Value::Null),
+        });
+        match call_validate(&client, gateway, &validate_body).await {
+            Ok(report) => {
+                history.push(IterateAttempt {
+                    iteration,
+                    raw: raw.chars().take(2000).collect(),
+                    status: AttemptStatus::Accepted,
+                });
+                return (StatusCode::OK, Json(IterateResponse {
+                    artifact,
+                    validation: report,
+                    iterations: iteration + 1,
+                    history,
+                })).into_response();
+            }
+            Err(err) => {
+                let err_summary = err.to_string();
+                history.push(IterateAttempt {
+                    iteration,
+                    raw: raw.chars().take(2000).collect(),
+                    status: AttemptStatus::ValidationFailed {
+                        error: serde_json::to_value(&err_summary).unwrap_or(serde_json::Value::Null),
+                    },
+                });
+                // Append validation feedback to prompt for next iter.
+                // The model sees concrete failure mode + retries with
+                // corrective context. This is the "observer correction"
+                // in Phase 43 PRD shape, simplified — the validator
+                // itself IS the observer for now.
+                current_prompt = format!(
+                    "{}\n\nPrior attempt failed validation:\n{}\n\nFix the specific issue above and respond with a corrected JSON object.",
+                    req.prompt, err_summary,
+                );
+                continue;
+            }
+        }
+    }
+
+    (StatusCode::UNPROCESSABLE_ENTITY, Json(IterateFailure {
+        error: format!("max iterations reached ({max_iter}) without passing validation"),
+        iterations: max_iter,
+        history,
+    })).into_response()
+}
+
+async fn call_chat(client: &reqwest::Client, gateway: &str, body: &serde_json::Value) -> Result<String, String> {
+    let resp = client.post(format!("{gateway}/v1/chat"))
+        .json(body)
+        .send()
+        .await
+        .map_err(|e| format!("chat hop: {e}"))?;
+    let status = resp.status();
+    if !status.is_success() {
+        let body = resp.text().await.unwrap_or_default();
+        return Err(format!("chat {}: {}", status, body.chars().take(300).collect::<String>()));
+    }
+    let parsed: serde_json::Value = resp.json().await.map_err(|e| format!("chat parse: {e}"))?;
+    Ok(parsed.pointer("/choices/0/message/content")
+        .and_then(|v| v.as_str())
+        .unwrap_or("")
+        .to_string())
+}
+
+async fn call_validate(client: &reqwest::Client, gateway: &str, body: &serde_json::Value) -> Result<serde_json::Value, String> {
+    let resp = client.post(format!("{gateway}/v1/validate"))
+        .json(body)
+        .send()
+        .await
+        .map_err(|e| format!("validate hop: {e}"))?;
+    let status = resp.status();
+    let parsed: serde_json::Value = resp.json().await.map_err(|e| format!("validate parse: {e}"))?;
+    if status.is_success() {
+        Ok(parsed)
+    } else {
+        // The /v1/validate endpoint returns a ValidationError JSON
+        // on 422; surface its structure verbatim so the prompt-
+        // appending step gets specific failure detail.
+        Err(serde_json::to_string(&parsed).unwrap_or_else(|_| format!("validation {} (unparseable body)", status)))
+    }
+}
+
+/// Extract the first JSON object from a model's output. Handles
+/// fenced code blocks (```json ... ```), bare braces, and stray
+/// prose around the JSON. Returns None on no extractable object.
+fn extract_json(raw: &str) -> Option<serde_json::Value> {
+    // Try fenced first.
+    let candidates: Vec<String> = {
+        let mut out = vec![];
+        let mut s = raw;
+        while let Some(start) = s.find("```") {
+            let after = &s[start + 3..];
+            // Skip optional language tag (json, etc.)
+            let body_start = after.find('\n').map(|n| n + 1).unwrap_or(0);
+            let body = &after[body_start..];
+            if let Some(end) = body.find("```") {
+                out.push(body[..end].trim().to_string());
+                s = &body[end + 3..];
+            } else { break; }
+        }
+        out
+    };
+    for c in &candidates {
+        if let Ok(v) = serde_json::from_str::<serde_json::Value>(c) {
+            if v.is_object() { return Some(v); }
+        }
+    }
+    // Fall back to outermost {...} balance.
+    let bytes = raw.as_bytes();
+    let mut depth = 0i32;
+    let mut start: Option<usize> = None;
+    for (i, &b) in bytes.iter().enumerate() {
+        match b {
+            b'{' => { if start.is_none() { start = Some(i); } depth += 1; }
+            b'}' => {
+                depth -= 1;
+                if depth == 0 {
+                    if let Some(s) = start {
+                        let slice = &raw[s..=i];
+                        if let Ok(v) = serde_json::from_str::<serde_json::Value>(slice) {
+                            if v.is_object() { return Some(v); }
+                        }
+                        start = None;
+                    }
+                }
+            }
+            _ => {}
+        }
+    }
+    None
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn extract_json_from_fenced_block() {
+        let raw = "Here's my answer:\n```json\n{\"fills\": [{\"candidate_id\": \"W-1\"}]}\n```\nDone.";
+        let v = extract_json(raw).unwrap();
+        assert!(v.get("fills").is_some());
+    }
+
+    #[test]
+    fn extract_json_from_bare_braces() {
+        let raw = "Here you go: {\"fills\": [{\"candidate_id\": \"W-2\"}]}";
+        let v = extract_json(raw).unwrap();
+        assert!(v.get("fills").is_some());
+    }
+
+    #[test]
+    fn extract_json_returns_none_on_no_object() {
+        assert!(extract_json("just prose, no json").is_none());
+    }
+
+    #[test]
+    fn extract_json_picks_first_balanced() {
+        let raw = "{\"a\":1} then {\"b\":2}";
+        let v = extract_json(raw).unwrap();
+        assert_eq!(v.get("a").and_then(|v| v.as_i64()), Some(1));
+    }
+}
diff --git a/crates/gateway/src/v1/mod.rs b/crates/gateway/src/v1/mod.rs
index 9af8d85..50b0990 100644
--- a/crates/gateway/src/v1/mod.rs
+++ b/crates/gateway/src/v1/mod.rs
@@ -19,6 +19,7 @@ pub mod claude;
 pub mod kimi;
 pub mod opencode;
 pub mod validate;
+pub mod iterate;
 pub mod langfuse_trace;
 pub mod mode;
 pub mod respond;
@@ -118,6 +119,7 @@ pub fn router(state: V1State) -> Router {
         .route("/mode/list", get(mode::list))
         .route("/mode/execute", post(mode::execute))
         .route("/validate", post(validate::validate))
+        .route("/iterate", post(iterate::iterate))
         .with_state(state)
 }