diff --git a/org-ops-core/Cargo.toml b/org-ops-core/Cargo.toml
index 3e33627..0b38d83 100644
--- a/org-ops-core/Cargo.toml
+++ b/org-ops-core/Cargo.toml
@@ -15,3 +15,7 @@ sha2 = "0.10"
 base64 = "0.22"
 urlencoding = "2"
 uuid = { version = "1", features = ["v4"] }
+hex = "0.4"
+
+[dev-dependencies]
+tempfile = "3"
diff --git a/org-ops-core/src/gsap_client.rs b/org-ops-core/src/gsap_client.rs
new file mode 100644
index 0000000..26cd58a
--- /dev/null
+++ b/org-ops-core/src/gsap_client.rs
@@ -0,0 +1,380 @@
+//! GSAP client — shell side of GCAP-SPEC-SHELLBOUND-BROKER-0001.
+//!
+//! Consumes Authorization Contexts from a GSAP broker (Capstone).
+//! Posts Completion Receipts after playbook execution.
+//!
+//! ```
+//! let client = GsapClient::new(broker_url, token, session_dir);
+//! let ac = client.authorize(&request)?;
+//! // execute playbook...
+//! client.complete(&ac, outcome)?;
+//! ```
+
+use anyhow::{anyhow, bail, Context, Result};
+use serde::{Deserialize, Serialize};
+use sha2::{Digest, Sha256};
+use std::collections::HashSet;
+use std::path::PathBuf;
+
+// ── AC schema (from broker) ──────────────────────────
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct AuthorizationContext {
+    pub gsap_version: String,
+    pub context_id: String,
+    pub issued_at: Option<String>,
+    pub expires_at: String,
+    pub principal: AcPrincipal,
+    pub accord: AcAccord,
+    pub operation: AcOperation,
+    pub identity_proof: AcIdentityProof,
+    pub signature: Option<String>,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct AcPrincipal {
+    pub did: String,
+    pub display_name: String,
+    pub broker_session_id: Option<String>,
+    pub driver_id: String,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct AcAccord {
+    pub template: String,
+    pub capability_mask: u8,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct AcOperation {
+    pub playbook: String,
+    pub corpus_entry_cid: String,
+    pub parameters_cid: String,
+    pub apply_authorized_cid: Option<String>,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct AcIdentityProof {
+    pub idp_vendor: String,
+    pub token_jti: String,
+    pub elevation_active: Vec<String>,
+    pub mfa_satisfied: bool,
+}
+
+// ── CR schema (to broker) ────────────────────────────
+
+#[derive(Debug, Serialize)]
+pub struct CompletionReceiptPayload {
+    pub context_id: String,
+    pub outcome: String,
+    pub completed_at: String,
+    pub chronicle_session_id: String,
+    pub behavioral_attestation_status: String,
+    pub observed_behavior_cid: String,
+    pub declared_behavior_cid: String,
+    pub ffc_did: String,
+    pub ffc_signature: String,
+}
+
+// ── Authorize request ────────────────────────────────
+
+#[derive(Debug, Serialize)]
+pub struct AuthorizeRequest {
+    pub playbook: String,
+    pub corpus_entry_cid: String,
+    pub parameters_cid: String,
+    pub accord_template: String,
+    pub driver_id: String,
+}
+
+// ── Broker response wrappers ─────────────────────────
+
+#[derive(Debug, Deserialize)]
+struct AuthorizeResponse {
+    context_id: Option<String>,
+    status: Option<String>,
+    ac_document: Option<AuthorizationContext>,
+    // For 202 pending elevation:
+    poll_token: Option<String>,
+    elevation: Option<serde_json::Value>,
+    // For errors:
+    error: Option<String>,
+}
+
+// ── Consumed context registry (GSAP R-22) ────────────
+
+struct ConsumedRegistry {
+    path: PathBuf,
+    consumed: HashSet<String>,
+}
+
+impl ConsumedRegistry {
+    fn new(session_dir: &PathBuf) -> Self {
+        let path = session_dir.join("consumed_contexts.json");
+        let consumed = std::fs::read_to_string(&path)
+            .ok()
+            .and_then(|s| serde_json::from_str(&s).ok())
+            .unwrap_or_default();
+        Self { path, consumed }
+    }
+
+    fn is_consumed(&self, id: &str) -> bool {
+        self.consumed.contains(id)
+    }
+
+    fn mark_consumed(&mut self, id: &str) -> Result<()> {
+        self.consumed.insert(id.to_string());
+        let json = serde_json::to_string(&self.consumed)?;
+        std::fs::write(&self.path, json)?;
+        Ok(())
+    }
+}
+
+// ── GSAP Client ──────────────────────────────────────
+
+pub struct GsapClient {
+    broker_url: String,
+    bearer_token: String,
+    session_dir: PathBuf,
+    http: reqwest::blocking::Client,
+}
+
+impl GsapClient {
+    pub fn new(broker_url: String, bearer_token: String, session_dir: PathBuf) -> Self {
+        std::fs::create_dir_all(&session_dir).ok();
+        Self {
+            broker_url,
+            bearer_token,
+            session_dir,
+            http: reqwest::blocking::Client::builder()
+                .timeout(std::time::Duration::from_secs(30))
+                .build()
+                .expect("HTTP client"),
+        }
+    }
+
+    /// Request an AC from the broker. Validates before returning.
+    pub fn authorize(
+        &self,
+        request: &AuthorizeRequest,
+        installed_corpus_cid: &str,
+        actual_parameters_cid: &str,
+    ) -> Result<AuthorizationContext> {
+        let url = format!("{}/api/v1/governance/authorize/", self.broker_url);
+        let resp = self.http.post(&url)
+            .bearer_auth(&self.bearer_token)
+            .json(request)
+            .send()
+            .context("Broker unreachable")?;
+
+        let status = resp.status();
+
+        if status == reqwest::StatusCode::ACCEPTED {
+            let body: AuthorizeResponse = resp.json()?;
+            if let Some(elevation) = body.elevation {
+                bail!("Elevation required: {}", serde_json::to_string_pretty(&elevation)?);
+            }
+            bail!("Pending authorization (poll_token: {:?})", body.poll_token);
+        }
+
+        if !status.is_success() {
+            let body: serde_json::Value = resp.json().unwrap_or_default();
+            bail!("Broker denied: {} {}", status, body);
+        }
+
+        let body: AuthorizeResponse = resp.json().context("Invalid AC response")?;
+        let ac = body.ac_document.ok_or_else(|| anyhow!("No ac_document in response"))?;
+
+        self.validate_ac(&ac, installed_corpus_cid, actual_parameters_cid)?;
+        Ok(ac)
+    }
+
+    fn validate_ac(
+        &self,
+        ac: &AuthorizationContext,
+        installed_corpus_cid: &str,
+        actual_parameters_cid: &str,
+    ) -> Result<()> {
+        let registry = ConsumedRegistry::new(&self.session_dir);
+
+        // R-22: single-use
+        if registry.is_consumed(&ac.context_id) {
+            bail!("AC replayed: {} already consumed", ac.context_id);
+        }
+
+        // R-23: corpus entry CID
+        if ac.operation.corpus_entry_cid != installed_corpus_cid {
+            bail!(
+                "Corpus mismatch: broker={} installed={}",
+                ac.operation.corpus_entry_cid, installed_corpus_cid
+            );
+        }
+
+        // R-24: parameters CID
+        if ac.operation.parameters_cid != actual_parameters_cid {
+            bail!("Parameters modified after broker authorization");
+        }
+
+        // R-20: signature (phase 1: presence check)
+        if ac.signature.is_none() {
+            eprintln!("GSAP: AC has no principal signature (dev mode)");
+        }
+
+        Ok(())
+    }
+
+    /// Post CR to broker. Retries 3 times (GSAP R-29).
+    pub fn complete(
+        &self,
+        ac: &AuthorizationContext,
+        outcome: &str,
+        chronicle_session_id: &str,
+    ) -> Result<()> {
+        // Mark consumed locally first
+        let mut registry = ConsumedRegistry::new(&self.session_dir);
+        registry.mark_consumed(&ac.context_id)?;
+
+        let payload = CompletionReceiptPayload {
+            context_id: ac.context_id.clone(),
+            outcome: outcome.to_string(),
+            completed_at: chrono_now(),
+            chronicle_session_id: chronicle_session_id.to_string(),
+            behavioral_attestation_status: "unavailable".to_string(),
+            observed_behavior_cid: String::new(),
+            declared_behavior_cid: String::new(),
+            ffc_did: std::env::var("FFC_DID").unwrap_or_default(),
+            ffc_signature: String::new(),
+        };
+
+        let url = format!("{}/api/v1/governance/complete/", self.broker_url);
+
+        for attempt in 0..3 {
+            match self.http.post(&url)
+                .json(&payload)
+                .send()
+            {
+                Ok(resp) if resp.status().is_success() => return Ok(()),
+                Ok(resp) => {
+                    let body: serde_json::Value = resp.json().unwrap_or_default();
+                    if attempt < 2 {
+                        eprintln!("GSAP CR attempt {} failed: {}", attempt + 1, body);
+                        std::thread::sleep(std::time::Duration::from_secs(2u64.pow(attempt as u32)));
+                    } else {
+                        self.store_pending_cr(&payload)?;
+                        bail!("CR delivery failed after 3 attempts: {}", body);
+                    }
+                }
+                Err(e) => {
+                    if attempt < 2 {
+                        eprintln!("GSAP CR attempt {} error: {}", attempt + 1, e);
+                        std::thread::sleep(std::time::Duration::from_secs(2u64.pow(attempt as u32)));
+                    } else {
+                        self.store_pending_cr(&payload)?;
+                        bail!("CR delivery failed: {}", e);
+                    }
+                }
+            }
+        }
+        Ok(())
+    }
+
+    fn store_pending_cr(&self, cr: &CompletionReceiptPayload) -> Result<()> {
+        let path = self.session_dir.join(format!("pending_cr_{}.json", &cr.context_id[..8]));
+        let json = serde_json::to_string_pretty(cr)?;
+        std::fs::write(path, json)?;
+        Ok(())
+    }
+}
+
+/// Compute sha256 CID of a byte slice.
+pub fn compute_cid(data: &[u8]) -> String {
+    let hash = Sha256::digest(data);
+    format!("sha256:{}", hex::encode(hash))
+}
+
+fn chrono_now() -> String {
+    // Simple ISO 8601 without chrono dependency
+    use std::time::SystemTime;
+    let dur = SystemTime::now().duration_since(SystemTime::UNIX_EPOCH).unwrap_or_default();
+    format!("1970-01-01T00:00:00Z+{}s", dur.as_secs()) // placeholder
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn make_ac(id: &str) -> AuthorizationContext {
+        AuthorizationContext {
+            gsap_version: "0.1.0".into(),
+            context_id: id.into(),
+            issued_at: Some("2026-01-01T00:00:00Z".into()),
+            expires_at: "2026-01-01T01:00:00Z".into(),
+            principal: AcPrincipal {
+                did: "did:web:test/p/test".into(),
+                display_name: "Test".into(),
+                broker_session_id: None,
+                driver_id: "kc-test".into(),
+            },
+            accord: AcAccord { template: "test".into(), capability_mask: 3 },
+            operation: AcOperation {
+                playbook: "test-echo".into(),
+                corpus_entry_cid: format!("sha256:{}", "a".repeat(64)),
+                parameters_cid: format!("sha256:{}", "b".repeat(64)),
+                apply_authorized_cid: None,
+            },
+            identity_proof: AcIdentityProof {
+                idp_vendor: "keycloak".into(),
+                token_jti: "jti".into(),
+                elevation_active: vec![],
+                mfa_satisfied: true,
+            },
+            signature: None,
+        }
+    }
+
+    #[test]
+    fn test_corpus_mismatch() {
+        let dir = tempfile::tempdir().unwrap();
+        let client = GsapClient::new("http://x".into(), "t".into(), dir.path().to_path_buf());
+        let ac = make_ac("ctx-1");
+        let r = client.validate_ac(&ac, &format!("sha256:{}", "z".repeat(64)), &format!("sha256:{}", "b".repeat(64)));
+        assert!(r.is_err());
+        assert!(r.unwrap_err().to_string().contains("Corpus mismatch"));
+    }
+
+    #[test]
+    fn test_params_modified() {
+        let dir = tempfile::tempdir().unwrap();
+        let client = GsapClient::new("http://x".into(), "t".into(), dir.path().to_path_buf());
+        let ac = make_ac("ctx-2");
+        let r = client.validate_ac(&ac, &format!("sha256:{}", "a".repeat(64)), &format!("sha256:{}", "z".repeat(64)));
+        assert!(r.is_err());
+        assert!(r.unwrap_err().to_string().contains("Parameters modified"));
+    }
+
+    #[test]
+    fn test_replay_rejected() {
+        let dir = tempfile::tempdir().unwrap();
+        let client = GsapClient::new("http://x".into(), "t".into(), dir.path().to_path_buf());
+        let ac = make_ac("ctx-3");
+        let corpus = format!("sha256:{}", "a".repeat(64));
+        let params = format!("sha256:{}", "b".repeat(64));
+        client.validate_ac(&ac, &corpus, &params).unwrap();
+
+        let mut reg = ConsumedRegistry::new(&dir.path().to_path_buf());
+        reg.mark_consumed("ctx-3").unwrap();
+
+        let r = client.validate_ac(&ac, &corpus, &params);
+        assert!(r.is_err());
+        assert!(r.unwrap_err().to_string().contains("replayed"));
+    }
+
+    #[test]
+    fn test_valid_ac() {
+        let dir = tempfile::tempdir().unwrap();
+        let client = GsapClient::new("http://x".into(), "t".into(), dir.path().to_path_buf());
+        let ac = make_ac("ctx-4");
+        let r = client.validate_ac(&ac, &format!("sha256:{}", "a".repeat(64)), &format!("sha256:{}", "b".repeat(64)));
+        assert!(r.is_ok());
+    }
+}
diff --git a/org-ops-core/src/lib.rs b/org-ops-core/src/lib.rs
index d9bae8c..245b901 100644
--- a/org-ops-core/src/lib.rs
+++ b/org-ops-core/src/lib.rs
@@ -18,6 +18,7 @@ pub mod playbook_commands;
 pub mod score_fetcher;
 pub mod session;
 pub mod traits;
+pub mod gsap_client;
 
 pub use auth_commands::{AuthCommands, AuthConfig};
 pub use config::OrgOpsConfig;