diff --git a/CHANGELOG.md b/CHANGELOG.md
index 14d5c40..bbe426e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,22 @@
 
 All notable changes to the Toolpath workspace are documented here.
 
+## Actor validation fixes — derived paths conform to the base schema — unreleased
+
+`derive_path` produced actor strings the base JSON Schema rejected: event steps
+used `provider:<name>`, system turns used `system:<provider>`, and `Role::Other`
+turns used `<role>:unknown` — none of those prefixes are in the schema's
+`actorRef` vocabulary. Separately the `actorRef` pattern's name segment
+disallowed `.`, so dotted model identifiers like `agent:gpt-5.5` failed
+validation.
+
+`toolpath`: `actorRef`'s name segment now allows `.`. `toolpath-convo`:
+`derive_path` emits `tool:<provider>` for event steps, system turns, and
+`Role::Other` turns (the role label stays in the change's `role` field), and a
+new test derives a path covering every actor variant and validates it against
+the embedded base schema so this can't regress. Touches `toolpath` and
+`toolpath-convo`; versions to be bumped at release.
+
 ## `path resume` — one-shot resume into a coding agent — 2026-05-09
 
 `path-cli` 0.9.0. New subcommand `path resume <input>` that fetches a
diff --git a/Cargo.lock b/Cargo.lock
index c7e90b3..cf42b08 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2690,6 +2690,7 @@ name = "toolpath-convo"
 version = "0.8.0"
 dependencies = [
  "chrono",
+ "jsonschema",
  "serde",
  "serde_json",
  "similar",
diff --git a/RFC.md b/RFC.md
index a3d062c..873575d 100644
--- a/RFC.md
+++ b/RFC.md
@@ -260,12 +260,17 @@ An **actor** is anything that performs steps. The short form is a string:
 ```
 human:alex
 agent:claude-code
+agent:gpt-5.5
 agent:claude-code/session-xyz
 tool:rustfmt
 tool:rustfmt/1.5.0
 ci:github-actions/workflow-123
 ```
 
+The prefix is one of `human`, `agent`, `tool`, or `ci`; the name segment may
+contain letters, digits, `.`, `_`, and `-`, with an optional `/`-delimited
+suffix.
+
 Actor strings are referenced in `step.actor`. Full actor definitions with
 identity and key information are provided in `meta.actors`.
 
diff --git a/crates/toolpath-codex/tests/fidelity.rs b/crates/toolpath-codex/tests/fidelity.rs
index 1af3f30..0441c73 100644
--- a/crates/toolpath-codex/tests/fidelity.rs
+++ b/crates/toolpath-codex/tests/fidelity.rs
@@ -151,9 +151,9 @@ fn head_equals_last_step_id() {
 #[test]
 fn actor_scheme_matches_source_role() {
     // Source role → actor-prefix mapping must be consistent:
-    //   "developer" | "system" → "system:*"
-    //   "user"                 → "human:*"
-    //   "assistant"            → "agent:*"
+    //   "user"                  → "human:*"
+    //   "assistant"             → "agent:*"
+    //   "developer" | "system"  → "tool:*"
     // We can't assert a strict 1:1 turn→step mapping (carrier turns
     // may collapse), but we can assert every observed role in the
     // view reaches a step with the expected actor prefix.
@@ -178,7 +178,7 @@ fn actor_scheme_matches_source_role() {
         assert!(prefixes.contains("agent"), "no step has an agent:* actor");
     }
     if system_seen {
-        assert!(prefixes.contains("system"), "no step has a system:* actor");
+        assert!(prefixes.contains("tool"), "no step has a tool:* actor");
     }
 }
 
diff --git a/crates/toolpath-convo/Cargo.toml b/crates/toolpath-convo/Cargo.toml
index 53a6598..9a23c0e 100644
--- a/crates/toolpath-convo/Cargo.toml
+++ b/crates/toolpath-convo/Cargo.toml
@@ -15,3 +15,6 @@ serde = { workspace = true }
 serde_json = { workspace = true }
 thiserror = { workspace = true }
 similar = { workspace = true }
+
+[dev-dependencies]
+jsonschema = { version = "0.46", default-features = false }
diff --git a/crates/toolpath-convo/src/derive.rs b/crates/toolpath-convo/src/derive.rs
index faabfb5..73893b4 100644
--- a/crates/toolpath-convo/src/derive.rs
+++ b/crates/toolpath-convo/src/derive.rs
@@ -318,7 +318,7 @@ pub fn derive_path(view: &ConversationView, config: &DeriveConfig) -> Path {
         } else {
             event.id.clone()
         };
-        let actor = format!("provider:{}", provider);
+        let actor = format!("tool:{}", provider);
         actors
             .entry(actor.clone())
             .or_insert_with(|| ActorDefinition {
@@ -448,8 +448,8 @@ fn actor_for_turn(turn: &Turn, provider: &str) -> String {
             let model = turn.model.as_deref().unwrap_or("unknown");
             format!("agent:{}", model)
         }
-        Role::System => format!("system:{}", provider),
-        Role::Other(s) => format!("{}:unknown", s),
+        Role::System => format!("tool:{}", provider),
+        Role::Other(_) => format!("tool:{}", provider),
     }
 }
 
@@ -477,10 +477,10 @@ fn record_actor(
             ..Default::default()
         }
     } else {
-        // system:*, other:*
         let name = actor.split_once(':').map(|x| x.1).unwrap_or("").to_string();
         ActorDefinition {
             name: Some(name),
+            provider: Some(provider.to_string()),
             ..Default::default()
         }
     };
@@ -719,7 +719,7 @@ mod tests {
         let turn = base_turn("t1", Role::System);
         let view = view_with(vec![turn]);
         let path = derive_path(&view, &DeriveConfig::default());
-        assert_eq!(path.steps[0].step.actor, "system:pi");
+        assert_eq!(path.steps[0].step.actor, "tool:pi");
     }
 
     #[test]
@@ -727,7 +727,7 @@ mod tests {
         let turn = base_turn("t1", Role::Other("tool".into()));
         let view = view_with(vec![turn]);
         let path = derive_path(&view, &DeriveConfig::default());
-        assert_eq!(path.steps[0].step.actor, "tool:unknown");
+        assert_eq!(path.steps[0].step.actor, "tool:pi");
     }
 
     #[test]
@@ -741,6 +741,39 @@ mod tests {
         assert_eq!(path.steps[1].step.parents, vec!["t1".to_string()]);
     }
 
+    #[test]
+    fn derived_path_validates_against_base_schema() {
+        let user = base_turn("t1", Role::User);
+        let mut assistant = base_turn("t2", Role::Assistant);
+        assistant.parent_id = Some("t1".into());
+        assistant.model = Some("gpt-5.5".into());
+        let system = base_turn("t3", Role::System);
+        let other = base_turn("t4", Role::Other("bash".into()));
+
+        let mut view = view_with(vec![user, assistant, system, other]);
+        view.events.push(crate::ConversationEvent {
+            id: "e1".into(),
+            timestamp: "2026-01-01T00:00:00Z".into(),
+            parent_id: None,
+            event_type: "attachment".into(),
+            data: HashMap::new(),
+        });
+
+        let path = derive_path(&view, &DeriveConfig::default());
+        let graph = serde_json::json!({
+            "graph": { "id": "g1" },
+            "paths": [serde_json::to_value(&path).unwrap()],
+        });
+
+        let schema: serde_json::Value = serde_json::from_str(toolpath::SCHEMA_JSON).unwrap();
+        let validator = jsonschema::validator_for(&schema).unwrap();
+        let errors: Vec<String> = validator
+            .iter_errors(&graph)
+            .map(|e| format!("at {}: {e}", e.instance_path()))
+            .collect();
+        assert!(errors.is_empty(), "base-schema violations:\n{}", errors.join("\n"));
+    }
+
     fn fw_tool(name: &str, id: &str, input: serde_json::Value) -> ToolInvocation {
         ToolInvocation {
             id: id.to_string(),
diff --git a/crates/toolpath/schema/toolpath.schema.json b/crates/toolpath/schema/toolpath.schema.json
index aab7962..2a3778c 100644
--- a/crates/toolpath/schema/toolpath.schema.json
+++ b/crates/toolpath/schema/toolpath.schema.json
@@ -13,9 +13,9 @@
 
     "actorRef": {
       "type": "string",
-      "pattern": "^(human|agent|tool|ci):[a-zA-Z0-9_-]+(\/[a-zA-Z0-9_.-]+)?$",
-      "description": "Actor reference string (e.g., 'human:alex', 'agent:claude-code', 'tool:rustfmt/1.5.0')",
-      "examples": ["human:alex", "agent:claude-code", "tool:rustfmt", "ci:github-actions"]
+      "pattern": "^(human|agent|tool|ci):[a-zA-Z0-9_.-]+(\/[a-zA-Z0-9_.-]+)?$",
+      "description": "Actor reference string (e.g., 'human:alex', 'agent:gpt-5.5', 'tool:rustfmt/1.5.0').",
+      "examples": ["human:alex", "agent:claude-code", "agent:gpt-5.5", "tool:rustfmt", "ci:github-actions"]
     },
 
     "identity": {
diff --git a/docs/agents/formats/codex.md b/docs/agents/formats/codex.md
index 83f738b..a5b3458 100644
--- a/docs/agents/formats/codex.md
+++ b/docs/agents/formats/codex.md
@@ -809,7 +809,7 @@ The mapping below is what the provider actually emits. Source:
 | `turn_context` (full) | `ConversationEvent` (round-trip preservation) |
 | `message` role `user` | `Turn { role: User }` → Step with `actor: "human:user"` |
 | `message` role `assistant` | `Turn { role: Assistant, model }` → Step with `actor: "agent:<model>"` |
-| `message` role `developer` | `Turn { role: System }` → Step with `actor: "system:codex"` |
+| `message` role `developer` | `Turn { role: System }` → Step with `actor: "tool:codex"` |
 | `reasoning.encrypted_content` | `Turn.extra["codex"]["reasoning_encrypted"]` (**not** `Turn.thinking` — it would render as ciphertext) |
 | `reasoning.summary[].text` / `reasoning.content[].text` (plaintext) | `Turn.thinking` on the next assistant turn |
 | `function_call` / `function_call_output` paired by `call_id` | `Turn.tool_uses[].{input, result}` |