diff --git a/docs/swarm/builder.md b/docs/swarm/builder.md
index 3fb34f63..3e1e2b83 100644
--- a/docs/swarm/builder.md
+++ b/docs/swarm/builder.md
@@ -28,8 +28,8 @@ Where it runs and how it's enabled: [`services.md`](services.md#builder).
 3. The builder runs `nix build` of `nix/builder/check-flake`'s `check` output
    with every input overridden:
    - `hyperhive` and `nixpkgs`: the sources the builder's own host was
-     deployed with, the same two a hive on that host renders into its meta
-     flake (`c0re.hyperhiveFlake`, `c0re.nixpkgsFlake`).
+     deployed with (`c0re.hyperhiveFlake`, `c0re.nixpkgsFlake`). A hive's meta
+     flake pins `hyperhive` by forge URL and rev instead.
    - `hyperhive-docs`: the `docs/` source a hive on that host renders into its
      meta flake (`c0re.hyperhiveDocs`). The check sets
      `services.hyperhive.agent.docs.source` from it, as the meta flake does,
diff --git a/flake.nix b/flake.nix
index 667b22c5..63f29f93 100644
--- a/flake.nix
+++ b/flake.nix
@@ -129,6 +129,7 @@
                 assets = lib.mkDefault self.packages.${pkgs.stdenv.hostPlatform.system}.assets;
                 xdgIcons = lib.mkDefault self.packages.${pkgs.stdenv.hostPlatform.system}.xdg-icons;
                 hyperhiveFlake = lib.mkDefault "${sources.hyperhiveFlakeSource}";
+                hyperhiveRev = lib.mkDefault (self.rev or null);
                 # Narrow docs/ source, threaded as its own meta-flake input
                 # so doc edits don't re-hash the whole flake source.
                 hyperhiveDocs = lib.mkDefault "${sources.hyperhiveDocsSource}";
diff --git a/hive-c0re/src/coordinator.rs b/hive-c0re/src/coordinator.rs
index 5351c473..d276fc1e 100644
--- a/hive-c0re/src/coordinator.rs
+++ b/hive-c0re/src/coordinator.rs
@@ -36,22 +36,18 @@ pub struct Coordinator {
     /// `get_full` for the per-card chip + side-panel viewer. See
     /// `build_logs.rs` for retention.
     pub build_logs: Arc<crate::build_logs::BuildLogs>,
-    /// URL of the hyperhive flake (no fragment). Inlined into per-agent
-    /// `flake.nix` files as `inputs.hyperhive.url`.
+    /// Store path of the hyperhive flake source (no fragment). Used to
+    /// identify the running revision (`current_flake_rev`); the meta flake
+    /// pins `hyperhive` by forge URL and [`Self::hyperhive_rev`] instead.
     pub hyperhive_flake: String,
     /// URL of the narrow `docs/` source (no fragment). Inlined into the
     /// meta `flake.nix` as `inputs.hyperhive-docs.url` and threaded to
     /// each agent as `services.hyperhive.agent.docs.source`. Its own store path
     /// so doc edits don't re-hash `hyperhive_flake`.
     pub hyperhive_docs_flake: String,
-    /// Store-path URL of the nixpkgs to wire into the meta flake as
-    /// `inputs.nixpkgs.url`. Populated by `--nixpkgs-flake` (set by the
-    /// NixOS module to `"path:${pkgs.path}"` so the meta flake always
-    /// tracks the same nixpkgs the host evaluated with — which is the
-    /// host's nixpkgs when `inputs.hyperhive.inputs.nixpkgs.follows =
-    /// "nixpkgs"` is set in the host flake). Empty string = legacy
-    /// `follows = "hyperhive/nixpkgs"` behaviour.
-    pub nixpkgs_flake: String,
+    /// Git rev of the hyperhive checkout this host runs. Pins the meta
+    /// flake's `hyperhive` input; `None` makes the meta render fail.
+    pub hyperhive_rev: Option<String>,
     /// Store path of the `claude-code` build every agent runs, written
     /// into each per-agent flake as `services.hyperhive.agent.claudeCodePath`. Set by
     /// the NixOS module option
@@ -203,7 +199,8 @@ pub struct HiveEnv {
     /// `services.hyperhive.agent.docs.source`. Separate from `hyperhive_flake`
     /// so a doc edit only re-locks this input, not the whole source.
     pub hyperhive_docs_flake: String,
-    pub nixpkgs_flake: String,
+    /// Git rev of the hyperhive checkout this host runs; see [`Coordinator::hyperhive_rev`].
+    pub hyperhive_rev: Option<String>,
     /// Store path of the `claude-code` agents run, or `None` for "each
     /// agent keeps the one out of its own nixpkgs". Travels into the
     /// container as `services.hyperhive.agent.claudeCodePath` — a plain string, kept
@@ -228,7 +225,7 @@ impl Default for HiveEnv {
         Self {
             hyperhive_flake: "/etc/hyperhive".to_string(),
             hyperhive_docs_flake: String::new(),
-            nixpkgs_flake: String::new(),
+            hyperhive_rev: None,
             claude_code_path: None,
             dashboard_port: 7000,
             agent_cpu_quota: "200%".to_string(),
@@ -405,7 +402,7 @@ impl Coordinator {
         let HiveEnv {
             hyperhive_flake,
             hyperhive_docs_flake,
-            nixpkgs_flake,
+            hyperhive_rev,
             claude_code_path,
             dashboard_port,
             agent_cpu_quota,
@@ -444,7 +441,7 @@ impl Coordinator {
             build_logs,
             hyperhive_flake,
             hyperhive_docs_flake,
-            nixpkgs_flake,
+            hyperhive_rev,
             claude_code_path,
             dashboard_port,
             agent_cpu_quota,
@@ -475,7 +472,7 @@ impl Coordinator {
         HiveEnv {
             hyperhive_flake: self.hyperhive_flake.clone(),
             hyperhive_docs_flake: self.hyperhive_docs_flake.clone(),
-            nixpkgs_flake: self.nixpkgs_flake.clone(),
+            hyperhive_rev: self.hyperhive_rev.clone(),
             claude_code_path: self.claude_code_path.clone(),
             dashboard_port: self.dashboard_port,
             agent_cpu_quota: self.agent_cpu_quota.clone(),
diff --git a/hive-c0re/src/main.rs b/hive-c0re/src/main.rs
index ddf6878d..4e4db6c9 100644
--- a/hive-c0re/src/main.rs
+++ b/hive-c0re/src/main.rs
@@ -78,15 +78,10 @@ enum Cmd {
         /// Path to the sqlite message store.
         #[arg(long, default_value = crate::paths::BROKER_DB)]
         db: PathBuf,
-        /// Override: URL of the hyperhive flake. Inlined into each
-        /// per-agent `flake.nix` as the `hyperhive` input.
+        /// Override: store path of the hyperhive flake source, used to
+        /// identify the running revision.
         #[arg(long)]
         hyperhive_flake: Option<String>,
-        /// Override: store-path URL of the nixpkgs to wire into the meta
-        /// flake as `inputs.nixpkgs.url`. Empty = legacy
-        /// `follows = "hyperhive/nixpkgs"` fallback.
-        #[arg(long)]
-        nixpkgs_flake: Option<String>,
         /// Override: dashboard HTTP port.
         #[arg(long)]
         dashboard_port: Option<u16>,
@@ -137,7 +132,6 @@ async fn main() -> Result<()> {
             config,
             db,
             hyperhive_flake,
-            nixpkgs_flake,
             dashboard_port,
             agent_cpu_quota,
             agent_memory_max,
@@ -161,9 +155,6 @@ async fn main() -> Result<()> {
             if let Some(v) = hyperhive_flake {
                 sc.env.hyperhive_flake = v;
             }
-            if let Some(v) = nixpkgs_flake {
-                sc.env.nixpkgs_flake = v;
-            }
             if let Some(v) = dashboard_port {
                 sc.env.dashboard_port = v;
             }
diff --git a/hive-c0re/src/meta.rs b/hive-c0re/src/meta.rs
index 56392479..de18461e 100644
--- a/hive-c0re/src/meta.rs
+++ b/hive-c0re/src/meta.rs
@@ -74,7 +74,7 @@ pub async fn sync_agents(hive: &HiveEnv, agents: &[AgentSpec]) -> Result<()> {
     let dir = crate::paths::meta_root();
     std::fs::create_dir_all(&dir).with_context(|| format!("create {}", dir.display()))?;
 
-    let new_flake = render_hive_flake(hive, agents);
+    let new_flake = render_hive_flake(hive, agents)?;
     let flake_path = dir.join("flake.nix");
     let on_disk = std::fs::read_to_string(&flake_path).unwrap_or_default();
     let initial = !dir.join(".git").exists();
@@ -327,13 +327,38 @@ pub async fn remove_permission_files() -> Result<()> {
     Ok(())
 }
 
+/// Pinned forge URL of the hyperhive flake: `git+<forge>/hyperhive/hyperhive.git?rev=<rev>`.
+/// Errors when the host has no rev, rather than rendering an unpinned URL.
+fn hyperhive_input_url(hive: &HiveEnv) -> Result<String> {
+    pinned_git_url(
+        &crate::forge::forge_git_url("hyperhive/hyperhive"),
+        hive.hyperhive_rev.as_deref(),
+    )
+}
+
+/// The pure half of [`hyperhive_input_url`], testable without `HIVE_FORGE_URL`.
+fn pinned_git_url(forge_git_url: &str, rev: Option<&str>) -> Result<String> {
+    let rev = rev.filter(|r| !r.is_empty()).context(
+        "hyperhive rev unknown: the host was built from a dirty tree \
+         (`self.rev` unset) and `services.hyperhive.c0re.hyperhiveRev` is not set",
+    )?;
+    Ok(format!("git+{forge_git_url}?rev={rev}"))
+}
+
 /// [`render_flake`] with its inputs taken from `hive`, as [`sync_agents`]
 /// renders it.
-fn render_hive_flake(hive: &HiveEnv, agents: &[AgentSpec]) -> String {
+fn render_hive_flake(hive: &HiveEnv, agents: &[AgentSpec]) -> Result<String> {
+    Ok(render_hive_flake_at(
+        hive,
+        &hyperhive_input_url(hive)?,
+        agents,
+    ))
+}
+
+fn render_hive_flake_at(hive: &HiveEnv, hyperhive_url: &str, agents: &[AgentSpec]) -> String {
     render_flake(
-        &hive.hyperhive_flake,
+        hyperhive_url,
         &hive.hyperhive_docs_flake,
-        &hive.nixpkgs_flake,
         hive.claude_code_path.as_deref(),
         hive.dashboard_port,
         agents,
@@ -341,17 +366,15 @@ fn render_hive_flake(hive: &HiveEnv, agents: &[AgentSpec]) -> String {
 }
 
 fn render_flake(
-    hyperhive_flake: &str,
+    hyperhive_url: &str,
     docs_flake: &str,
-    nixpkgs_flake: &str,
     claude_code_path: Option<&str>,
     dashboard_port: u16,
     agents: &[AgentSpec],
 ) -> String {
     render_flake_with_lookup(
-        hyperhive_flake,
+        hyperhive_url,
         docs_flake,
-        nixpkgs_flake,
         claude_code_path,
         dashboard_port,
         agents,
@@ -732,9 +755,8 @@ fn agent_canonical_inputs(name: &str) -> Vec<&'static str> {
               contiguous fmt block, splitting it would just hide the shape"
 )]
 fn render_flake_with_lookup<F>(
-    hyperhive_flake: &str,
+    hyperhive_url: &str,
     docs_flake: &str,
-    nixpkgs_flake: &str,
     claude_code_path: Option<&str>,
     dashboard_port: u16,
     agents: &[AgentSpec],
@@ -746,31 +768,12 @@ where
     use std::fmt::Write as _;
     let mut out = String::new();
     out.push_str("{\n  description = \"hyperhive deployed agents\";\n  inputs = {\n");
-    // `nixpkgs` is a top-level meta input with an explicit store-path URL.
-    // `hyperhive` then follows it via `hyperhive.inputs.nixpkgs.follows`.
-    // This cascades through to every agent because
-    // `agent-<n>.inputs.nixpkgs.follows = "nixpkgs"` resolves to the same
-    // top-level node.
-    //
-    // Why an explicit `path:` URL instead of
-    // `nixpkgs.follows = "hyperhive/nixpkgs"`:
-    // meta points to hyperhive's *store path* as its flake input, so nix
-    // reads hyperhive's own pinned lock when evaluating that input — the
-    // host-level `follows` the operator set never propagates. Injecting the
-    // evaluated `pkgs.path` directly at nix-module evaluation time is the
-    // only reliable way to honour the host's channel choice.
-    //
-    // Fallback (flake arg empty): legacy `follows` wiring — used when
-    // hive-c0re is not built with this option wired up.
-    if nixpkgs_flake.is_empty() {
-        // Legacy path: meta defers to hyperhive's own lock.
-        let _ = writeln!(out, "    hyperhive.url = \"{hyperhive_flake}\";");
-        out.push_str("    nixpkgs.follows = \"hyperhive/nixpkgs\";\n");
-    } else {
-        let _ = writeln!(out, "    nixpkgs.url = \"{nixpkgs_flake}\";");
-        let _ = writeln!(out, "    hyperhive.url = \"{hyperhive_flake}\";");
-        out.push_str("    hyperhive.inputs.nixpkgs.follows = \"nixpkgs\";\n");
-    }
+    // `hyperhive` is pinned by forge URL and rev, so the flake resolves on
+    // any machine that can reach the forge. `nixpkgs` follows hyperhive's
+    // own pin, which cascades to every agent because
+    // `agent-<n>.inputs.nixpkgs.follows = "nixpkgs"` resolves to this node.
+    let _ = writeln!(out, "    hyperhive.url = \"{hyperhive_url}\";");
+    out.push_str("    nixpkgs.follows = \"hyperhive/nixpkgs\";\n");
     // Narrow `docs/` source as its own input so a doc edit only
     // re-locks THIS input instead of re-hashing the whole `hyperhive`
     // source. Threaded to each agent below as `services.hyperhive.agent.docs.source`.
@@ -1283,28 +1286,43 @@ mod tests {
     }
 
     #[test]
-    fn render_flake_uses_explicit_nixpkgs_url_when_provided() {
+    fn pinned_git_url_carries_the_rev_and_refuses_without_one() {
+        assert_eq!(
+            pinned_git_url(
+                "https://forge.example/hyperhive/hyperhive.git",
+                Some("abc123")
+            )
+            .unwrap(),
+            "git+https://forge.example/hyperhive/hyperhive.git?rev=abc123"
+        );
+        for missing in [None, Some("")] {
+            let err = pinned_git_url("https://forge.example/x.git", missing).unwrap_err();
+            assert!(err.to_string().contains("rev unknown"), "{err}");
+        }
+    }
+
+    #[test]
+    fn render_flake_pins_hyperhive_by_url_and_follows_its_nixpkgs() {
         let out = render_flake(
-            "github:example/hyperhive",
+            "git+https://forge.example/hyperhive/hyperhive.git?rev=0123abcd",
             "path:/nix/store/bbbb-hyperhive-docs-source",
-            "path:/nix/store/aaaa-nixpkgs-source",
             None,
             8000,
             &[sample_spec("alice", 9001)],
         );
-        // nixpkgs is a top-level input with an explicit URL; hyperhive
-        // follows it.
         assert!(
-            out.contains("nixpkgs.url = \"path:/nix/store/aaaa-nixpkgs-source\""),
-            "expected explicit nixpkgs.url:\n{out}"
+            out.contains(
+                "hyperhive.url = \"git+https://forge.example/hyperhive/hyperhive.git?rev=0123abcd\";"
+            ),
+            "expected hyperhive pinned by forge URL:\n{out}"
         );
         assert!(
-            out.contains("hyperhive.inputs.nixpkgs.follows = \"nixpkgs\""),
-            "expected hyperhive.inputs.nixpkgs.follows:\n{out}"
+            out.contains("nixpkgs.follows = \"hyperhive/nixpkgs\";"),
+            "expected nixpkgs to follow hyperhive:\n{out}"
         );
         assert!(
-            !out.contains("nixpkgs.follows = \"hyperhive"),
-            "old-style follows must not appear when flake args are set:\n{out}"
+            !out.contains("nixpkgs.url") && !out.contains("hyperhive.inputs.nixpkgs"),
+            "no separate nixpkgs input:\n{out}"
         );
         // the narrow docs source is its own non-flake input, and each
         // agent's docs dir resolves from it rather than services.hyperhive.agent.packages.reference-docs.
@@ -1329,9 +1347,8 @@ mod tests {
         // Legacy / not-wired-up: empty docs_flake emits no docs input and
         // leaves each agent on the harness default (services.hyperhive.agent.packages.reference-docs).
         let out = render_flake(
-            "github:example/hyperhive",
+            "git+https://forge.example/hyperhive/hyperhive.git?rev=0123abcd",
             "",
-            "path:/nix/store/aaaa-nixpkgs-source",
             None,
             8000,
             &[sample_spec("alice", 9001)],
@@ -1345,9 +1362,8 @@ mod tests {
     #[test]
     fn render_flake_names_each_agent_container_after_the_agent() {
         let out = render_flake(
-            "github:example/hyperhive",
+            "git+https://forge.example/hyperhive/hyperhive.git?rev=0123abcd",
             "",
-            "path:/nix/store/aaaa-nixpkgs-source",
             None,
             8000,
             &[sample_spec("alice", 9001)],
@@ -1383,9 +1399,8 @@ mod tests {
         // input would re-copy it as a reference-less `-source` and strip
         // the closure the binary actually needs.
         let out = render_flake(
-            "github:example/hyperhive",
+            "git+https://forge.example/hyperhive/hyperhive.git?rev=0123abcd",
             "path:/nix/store/bbbb-hyperhive-docs-source",
-            "path:/nix/store/aaaa-nixpkgs-source",
             Some("/nix/store/cccc-claude-code-2.1.220"),
             8000,
             &[sample_spec("alice", 9001)],
@@ -1409,9 +1424,8 @@ mod tests {
         // in `environment.systemPackages`, which is what makes the
         // unpinned case self-contained).
         let out = render_flake(
-            "github:example/hyperhive",
+            "git+https://forge.example/hyperhive/hyperhive.git?rev=0123abcd",
             "path:/nix/store/bbbb-hyperhive-docs-source",
-            "path:/nix/store/aaaa-nixpkgs-source",
             None,
             8000,
             &[sample_spec("alice", 9001)],
@@ -1422,28 +1436,6 @@ mod tests {
         );
     }
 
-    #[test]
-    fn render_flake_falls_back_to_follows_when_nixpkgs_flake_empty() {
-        // Empty nixpkgs_flake → legacy follows behaviour (backward compat
-        // for any code path that can't inject pkgs.path).
-        let out = render_flake(
-            "github:example/hyperhive",
-            "path:/nix/store/bbbb-hyperhive-docs-source",
-            "",
-            None,
-            8000,
-            &[sample_spec("alice", 9001)],
-        );
-        assert!(
-            out.contains("nixpkgs.follows = \"hyperhive/nixpkgs\""),
-            "expected fallback follows:\n{out}"
-        );
-        assert!(
-            !out.contains("nixpkgs.url ="),
-            "no explicit url should be emitted in fallback mode:\n{out}"
-        );
-    }
-
     #[test]
     fn render_flake_emits_follows_for_agents_declaring_nixpkgs() {
         // Stub lookup: pretend `bitburner` + `dmatrix` declare `nixpkgs`
@@ -1455,9 +1447,8 @@ mod tests {
             }
         };
         let out = render_flake_with_lookup(
-            "github:example/hyperhive",
+            "git+https://forge.example/hyperhive/hyperhive.git?rev=0123abcd",
             "path:/nix/store/bbbb-hyperhive-docs-source",
-            "path:/nix/store/aaaa-nixpkgs-source",
             None,
             8000,
             &[
@@ -1486,9 +1477,8 @@ mod tests {
     #[test]
     fn render_flake_builds_every_agent_from_agent_base() {
         let out = render_flake(
-            "github:example/hyperhive",
+            "git+https://forge.example/hyperhive/hyperhive.git?rev=0123abcd",
             "path:/nix/store/bbbb-hyperhive-docs-source",
-            "path:/nix/store/aaaa-nixpkgs-source",
             None,
             8000,
             &[sample_spec("alice", 9001), sample_spec("ruth", 9002)],
@@ -1513,9 +1503,8 @@ mod tests {
     #[test]
     fn render_flake_skips_canonical_follows_when_lookup_returns_empty() {
         let out = render_flake_with_lookup(
-            "github:example/hyperhive",
+            "git+https://forge.example/hyperhive/hyperhive.git?rev=0123abcd",
             "path:/nix/store/bbbb-hyperhive-docs-source",
-            "path:/nix/store/aaaa-nixpkgs-source",
             None,
             8000,
             &[sample_spec("alice", 9001)],
@@ -1543,9 +1532,8 @@ mod tests {
             ..sample_spec("droid", 9002)
         };
         let out = render_flake_with_lookup(
-            "github:example/hyperhive",
+            "git+https://forge.example/hyperhive/hyperhive.git?rev=0123abcd",
             "path:/nix/store/bbbb-hyperhive-docs-source",
-            "path:/nix/store/aaaa-nixpkgs-source",
             None,
             8000,
             &[sample_spec("alice", 9001), android],
@@ -1596,9 +1584,8 @@ mod tests {
             std::env::set_var("HIVE_FORGE_URL", "http://forge.example.test");
         }
         let out = render_flake(
-            "github:example/hyperhive",
+            "git+https://forge.example/hyperhive/hyperhive.git?rev=0123abcd",
             "path:/nix/store/bbbb-hyperhive-docs-source",
-            "path:/nix/store/aaaa-nixpkgs-source",
             None,
             8000,
             &[sample_spec("alice", 9001)],
@@ -1639,9 +1626,8 @@ mod tests {
                 std::env::set_var(VARS[1], domain);
             }
             render_flake(
-                "github:example/hyperhive",
+                "git+https://forge.example/hyperhive/hyperhive.git?rev=0123abcd",
                 "path:/nix/store/bbbb-hyperhive-docs-source",
-                "path:/nix/store/aaaa-nixpkgs-source",
                 None,
                 8000,
                 &[sample_spec("alice", 9001)],
@@ -1836,9 +1822,8 @@ mod tests {
             std::env::set_var("HIVE_MATRIX_URL", "http://matrix.example.test");
         }
         let out = render_flake(
-            "github:example/hyperhive",
+            "git+https://forge.example/hyperhive/hyperhive.git?rev=0123abcd",
             "path:/nix/store/bbbb-hyperhive-docs-source",
-            "path:/nix/store/aaaa-nixpkgs-source",
             None,
             8000,
             &[sample_spec("alice", 9001)],
@@ -1870,9 +1855,8 @@ mod tests {
         // forge being reachable. The forge `agent-configs/<n>` repos stay the
         // review surface, but they are not the flake's build input.
         let out = render_flake(
-            "github:example/hyperhive",
+            "git+https://forge.example/hyperhive/hyperhive.git?rev=0123abcd",
             "path:/nix/store/bbbb-hyperhive-docs-source",
-            "path:/nix/store/aaaa-nixpkgs-source",
             None,
             8000,
             &[sample_spec("alice", 9001)],
@@ -1886,8 +1870,8 @@ mod tests {
             "expected the agent input to point at the local applied mirror ({want}):\n{out}"
         );
         assert!(
-            !out.contains("git+http"),
-            "no forge git+http URL must remain in the rendered flake:\n{out}"
+            !out.contains("agent-alice.url = \"git+http"),
+            "no forge git+http URL must remain for the agent input:\n{out}"
         );
     }
 
@@ -1912,9 +1896,8 @@ mod tests {
 
         let render = || {
             render_flake(
-                "github:example/hyperhive",
+                "git+https://forge.example/hyperhive/hyperhive.git?rev=0123abcd",
                 "path:/nix/store/bbbb-hyperhive-docs-source",
-                "path:/nix/store/aaaa-nixpkgs-source",
                 None,
                 8000,
                 &[sample_spec("alice", 9001)],
@@ -2002,9 +1985,8 @@ mod tests {
         // SAFETY: serialised by the guard above; restored before returning.
         let render = || {
             render_flake(
-                "github:example/hyperhive",
+                "git+https://forge.example/hyperhive/hyperhive.git?rev=0123abcd",
                 "path:/nix/store/bbbb-hyperhive-docs-source",
-                "path:/nix/store/aaaa-nixpkgs-source",
                 None,
                 8000,
                 &[sample_spec("alice", 9001)],
@@ -2074,9 +2056,8 @@ mod tests {
         // SAFETY: serialised by the guard above; restored before returning.
         let render = || {
             render_flake(
-                "github:example/hyperhive",
+                "git+https://forge.example/hyperhive/hyperhive.git?rev=0123abcd",
                 "path:/nix/store/bbbb-hyperhive-docs-source",
-                "path:/nix/store/aaaa-nixpkgs-source",
                 None,
                 8000,
                 &[sample_spec("alice", 9001)],
@@ -2112,8 +2093,16 @@ mod tests {
             ..HiveEnv::default()
         };
         let agents = [sample_spec("alice", 9001)];
-        let small = render_hive_flake(&hive("4G"), &agents);
-        let large = render_hive_flake(&hive("16G"), &agents);
+        let small = render_hive_flake_at(
+            &hive("4G"),
+            "git+https://forge.example/h.git?rev=abc",
+            &agents,
+        );
+        let large = render_hive_flake_at(
+            &hive("16G"),
+            "git+https://forge.example/h.git?rev=abc",
+            &agents,
+        );
         assert_eq!(
             small, large,
             "the rendered flake must not depend on the memory cap"
diff --git a/nix/host-modules/hive-c0re/default.nix b/nix/host-modules/hive-c0re/default.nix
index 24e20cd4..15ddae87 100644
--- a/nix/host-modules/hive-c0re/default.nix
+++ b/nix/host-modules/hive-c0re/default.nix
@@ -97,7 +97,7 @@ let
   serveConfigJson = builtins.toJSON {
     hyperhive_flake = cfg.hyperhiveFlake;
     hyperhive_docs_flake = cfg.hyperhiveDocs;
-    nixpkgs_flake = cfg.nixpkgsFlake;
+    hyperhive_rev = cfg.hyperhiveRev;
     # The `claude-code` every agent runs, or null for "each agent keeps
     # the one out of its own nixpkgs". `builtins.toJSON` serialises a
     # derivation as its out path (and null as null), so the package goes
diff --git a/nix/host-modules/hive-c0re/options.nix b/nix/host-modules/hive-c0re/options.nix
index 6abf7a29..47749ae1 100644
--- a/nix/host-modules/hive-c0re/options.nix
+++ b/nix/host-modules/hive-c0re/options.nix
@@ -70,12 +70,24 @@
       type = lib.types.str;
       defaultText = lib.literalMD "the hyperhive flake's own filtered source store path";
       description = ''
-        URL of the hyperhive flake (no fragment). Inlined into each
-        per-agent `flake.nix` at `inputs.hyperhive.url`. The per-agent
-        flake then pulls `hyperhive.nixosConfigurations.agent-base` to
-        build the container. Wired by `nixosModules.default` to this
-        flake's own filtered source — only override if you want agents
-        tracking a different ref.
+        Store path of the hyperhive flake source (no fragment). hive-c0re
+        reads it to tell which revision is running, and the swarm builder
+        builds on it. The meta flake does not use it: that pins
+        `hyperhive` by forge URL and `hyperhiveRev`. Wired by
+        `nixosModules.default` to this flake's own filtered source.
+      '';
+    };
+    hyperhiveRev = lib.mkOption {
+      type = lib.types.nullOr lib.types.str;
+      default = null;
+      defaultText = lib.literalMD "the hyperhive flake's own `self.rev`";
+      description = ''
+        Git rev of the hyperhive checkout this host runs. hive-c0re pins
+        the generated meta flake's `hyperhive` input to
+        `git+<forge>/hyperhive/hyperhive.git?rev=<rev>`, and `nixpkgs`
+        follows that input. Wired by `nixosModules.default` from
+        `self.rev`, which a dirty tree does not have; with `null`,
+        hive-c0re refuses to render the meta flake.
       '';
     };
     hyperhiveDocs = lib.mkOption {
@@ -105,20 +117,12 @@
       default = "path:${pkgs.path}";
       defaultText = lib.literalMD "`\"path:\${pkgs.path}\"`";
       description = ''
-        Store-path URL for the `nixpkgs` input in the generated meta
-        flake. The meta flake declares this as a top-level input and
-        wires `inputs.hyperhive.inputs.nixpkgs.follows = "nixpkgs"` so
-        every agent container evaluates with this exact nixpkgs.
+        Store-path URL of the nixpkgs the swarm builder's check flake
+        builds on. The generated meta flake does not use it: its `nixpkgs`
+        follows `hyperhive/nixpkgs`.
 
-        Defaults to `"path:''${pkgs.path}"` — the store path of the
-        nixpkgs the host NixOS module was evaluated with. When the
-        operator sets `inputs.hyperhive.inputs.nixpkgs.follows =
-        "nixpkgs"` in their host flake, `pkgs.path` resolves to the
-        host's own nixpkgs, so agents transparently track the same
-        channel as the host.
-
-        Override to pin agents to a specific nixpkgs version regardless
-        of the host's channel.
+        Defaults to `"path:''${pkgs.path}"`, the nixpkgs the host NixOS
+        module was evaluated with.
       '';
     };
     preBuildAgentTemplates = lib.mkOption {
@@ -340,7 +344,7 @@
       description = ''
         The `claude-code` build every agent on this hive runs, or `null` (the
         default) to leave each agent on the `claude-code` from its own
-        nixpkgs — i.e. whatever `c0re.nixpkgsFlake` resolves to.
+        nixpkgs — i.e. the nixpkgs pinned by hyperhive's own `flake.lock`.
 
         This is the one binary the whole hive is built around, and it
         moves fast enough that a release channel routinely trails
diff --git a/nix/module-eval/builder.nix b/nix/module-eval/builder.nix
index 7b7f9ef1..2f84f74f 100644
--- a/nix/module-eval/builder.nix
+++ b/nix/module-eval/builder.nix
@@ -135,8 +135,8 @@ let
         && lib.elem "swarm-bao-pki.service" c.after;
     }
     {
-      # The check builds on the sources a hive on this host would render into
-      # its meta flake, so a green check means the same base.
+      # The check builds on the sources this host was deployed with, so a green check means
+      # the same hyperhive, docs and nixpkgs base.
       name = "the builder builds on the hyperhive, docs and nixpkgs this host's hives use";
       ok =
         env.SWARM_BUILDER_HYPERHIVE_FLAKE == withBuilder.services.hyperhive.c0re.hyperhiveFlake