diff --git a/crates/aura-cli/src/graph_construct.rs b/crates/aura-cli/src/graph_construct.rs
index a043a55..ceda7e9 100644
--- a/crates/aura-cli/src/graph_construct.rs
+++ b/crates/aura-cli/src/graph_construct.rs
@@ -208,8 +208,29 @@ pub fn introspect_cmd(rest: &[&str]) {
                 }
             }
         }
+        ["--content-id"] => {
+            // the content id (#158) of the op-list's canonical blueprint: SHA256 (hex)
+            // of the same `blueprint_to_json` bytes `graph build` emits, via the one
+            // shared `crate::content_id` primitive `topology_hash` also uses — so this
+            // surface and hashing a `graph build` output agree by construction.
+            use std::io::Read;
+            let mut doc = String::new();
+            if let Err(e) = std::io::stdin().read_to_string(&mut doc) {
+                eprintln!("aura: reading stdin: {e}");
+                std::process::exit(2);
+            }
+            match build_from_str(&doc) {
+                Ok(json) => println!("{}", crate::content_id(&json)),
+                Err(m) => {
+                    eprintln!("aura: {m}");
+                    std::process::exit(2);
+                }
+            }
+        }
         _ => {
-            eprintln!("aura: usage: aura graph introspect --vocabulary | --node <T> | --unwired");
+            eprintln!(
+                "aura: usage: aura graph introspect --vocabulary | --node <T> | --unwired | --content-id"
+            );
             std::process::exit(2);
         }
     }
diff --git a/crates/aura-cli/src/main.rs b/crates/aura-cli/src/main.rs
index e1c2729..a22ace8 100644
--- a/crates/aura-cli/src/main.rs
+++ b/crates/aura-cli/src/main.rs
@@ -2816,16 +2816,23 @@ fn stage1_signal(fast_len: Option<i64>, slow_len: Option<i64>) -> Composite {
     g.build().expect("stage1 signal wiring resolves")
 }
 
-/// SHA256 (hex) of the canonical (#164, no-trailing-newline) serialization of a
-/// signal blueprint — the run's `topology_hash` (#158). Research-side (aura-cli),
-/// off the frozen engine (invariant 8).
-fn topology_hash(signal: &Composite) -> String {
+/// SHA256 (hex) of a canonical (#164) blueprint JSON string — the content id (#158).
+/// The single hashing primitive, shared by [`topology_hash`] (from a live `Composite`)
+/// and the op-script `graph introspect --content-id` path (`crate::content_id`), so the
+/// two surfaces agree by construction over the same canonical bytes. Research-side
+/// (aura-cli), off the frozen engine (invariant 8).
+fn content_id(canonical_json: &str) -> String {
     use sha2::{Digest, Sha256};
-    let canonical = blueprint_to_json(signal).expect("a buildable signal serializes");
-    let digest = Sha256::digest(canonical.as_bytes());
+    let digest = Sha256::digest(canonical_json.as_bytes());
     digest.iter().map(|b| format!("{b:02x}")).collect()
 }
 
+/// SHA256 (hex) of the canonical (#164, no-trailing-newline) serialization of a
+/// signal blueprint — the run's `topology_hash` (#158).
+fn topology_hash(signal: &Composite) -> String {
+    content_id(&blueprint_to_json(signal).expect("a buildable signal serializes"))
+}
+
 /// The Stage-1 R harness topology, shared by the single run and the sweep. The two
 /// signal knobs are bound when `Some` (single run — identical to the old
 /// build-time bind, output byte-unchanged) and left free when `None` (sweep — they
@@ -5506,6 +5513,43 @@ mod tests {
         assert_ne!(h, topology_hash(&stage1_signal(Some(3), Some(4))), "different topology -> different hash");
     }
 
+    /// #158 acc 1 (content-id stability across the store round-trip): a blueprint's content
+    /// id survives serialize -> reload -> re-serialize (#164 idempotence) — the property
+    /// content-addressed reproduction rests on (the stored bytes re-hash to the members'
+    /// topology_hash). `content_id` is the shared primitive `topology_hash` uses.
+    #[test]
+    fn content_id_is_stable_across_the_store_round_trip() {
+        let json = blueprint_to_json(&stage1_signal(Some(2), Some(4))).expect("serializes");
+        let id = content_id(&json);
+        assert_eq!(id.len(), 64, "a 64-hex sha256");
+        let reloaded = blueprint_from_json(&json, &|t| std_vocabulary(t)).expect("reloads");
+        assert_eq!(
+            content_id(&blueprint_to_json(&reloaded).expect("re-serializes")),
+            id,
+            "content id survives serialize -> reload -> re-serialize (#164)"
+        );
+    }
+
+    /// #158 acc 3 (Tier-1 format addition leaves the content id unchanged): a Tier-1
+    /// optional field the blueprint does not use is tolerated by the loader (#156) and
+    /// absent from the canonical omit-defaults form, so re-serializing yields the same
+    /// bytes and thus the same content id.
+    #[test]
+    fn content_id_is_stable_across_a_tolerated_tier1_field() {
+        let base = blueprint_to_json(&stage1_signal(Some(2), Some(4))).expect("serializes");
+        // a future Tier-1 optional field injected at the top level (the blueprint does not use it).
+        let with_extra =
+            base.replacen("{\"format_version\":1,", "{\"format_version\":1,\"future_optional\":123,", 1);
+        assert_ne!(base, with_extra, "the doc actually carries the extra field");
+        let reparsed = blueprint_from_json(&with_extra, &|t| std_vocabulary(t))
+            .expect("loader tolerates an unknown Tier-1 field (#156)");
+        assert_eq!(
+            content_id(&blueprint_to_json(&reparsed).expect("re-serializes")),
+            content_id(&base),
+            "a Tier-1 optional the blueprint does not use leaves the content id unchanged"
+        );
+    }
+
     #[test]
     fn parse_mc_args_bare_and_name_route_to_synthetic() {
         assert_eq!(parse_mc_args(&[]), Ok(McArgs::Synthetic { name: "mc".to_string(), persist: false }));
diff --git a/crates/aura-cli/tests/graph_construct.rs b/crates/aura-cli/tests/graph_construct.rs
index 278b72e..31efbd0 100644
--- a/crates/aura-cli/tests/graph_construct.rs
+++ b/crates/aura-cli/tests/graph_construct.rs
@@ -212,3 +212,42 @@ fn graph_build_renders_role_kind_mismatch_at_finalize_by_identifier() {
     assert!(!stderr.contains("RoleKindMismatch"),
         "does not leak the Debug variant name: {stderr}");
 }
+
+/// Property (#158 acc 1, the content-id surface): `aura graph introspect --content-id`
+/// prints the 64-hex SHA256 of the op-script's canonical blueprint — deterministic across
+/// runs and distinct for a structurally different topology. It is the same hash `aura run`
+/// stamps as `topology_hash` (both via the one `content_id` primitive over the canonical
+/// `blueprint_to_json` bytes), so a data-authored topology has a stable, comparable content
+/// id. (Note: an op-script and the Rust `stage1_signal` builder produce *different*
+/// canonical forms — composite debug-name, an unbound `Bias.scale` — so they are different
+/// topologies by the byte definition; content-addressing keys on the canonical form.)
+#[test]
+fn graph_introspect_content_id_is_deterministic_and_distinguishes() {
+    let (a, _e, ok) = run(&["graph", "introspect", "--content-id"], SIGNAL_DOC);
+    assert!(ok, "exit success");
+    let id = a.trim();
+    assert_eq!(id.len(), 64, "a 64-hex SHA256 content id: {id:?}");
+    assert!(id.chars().all(|c| c.is_ascii_hexdigit()), "hex only: {id:?}");
+
+    // deterministic: the same op-script yields the same content id.
+    let (b, _e2, ok2) = run(&["graph", "introspect", "--content-id"], SIGNAL_DOC);
+    assert!(ok2, "exit success");
+    assert_eq!(id, b.trim(), "same op-script -> same content id");
+
+    // distinguishes: a structurally different topology (slow length 4 -> 5) differs.
+    let other = SIGNAL_DOC.replace("\"I64\":4", "\"I64\":5");
+    let (c, _e3, ok3) = run(&["graph", "introspect", "--content-id"], &other);
+    assert!(ok3, "exit success");
+    assert_ne!(id, c.trim(), "a different topology -> a different content id");
+}
+
+/// Property (negative): `aura graph introspect --content-id` on a malformed op-list exits
+/// non-zero with the cause on stderr and prints no content id — it fails cleanly, never a
+/// partial/garbage hash.
+#[test]
+fn graph_introspect_content_id_rejects_a_bad_document() {
+    let (stdout, stderr, ok) = run(&["graph", "introspect", "--content-id"], r#"[{"op":"add","type":"Nope"}]"#);
+    assert!(!ok, "non-zero exit on a bad op-list");
+    assert!(stdout.is_empty(), "no content id emitted on error: {stdout}");
+    assert!(stderr.contains("Nope"), "names the cause: {stderr}");
+}