diff --git a/_primitives/_rust/kei-agent-runtime/src/lib.rs b/_primitives/_rust/kei-agent-runtime/src/lib.rs
index 52f3283..7b4424a 100644
--- a/_primitives/_rust/kei-agent-runtime/src/lib.rs
+++ b/_primitives/_rust/kei-agent-runtime/src/lib.rs
@@ -7,6 +7,7 @@
 //!   - `verifies`   — 8 on-return verify capabilities
 //!   - `compose`    — task.toml + role + capabilities → prompt.md
 //!   - `spawn`      — prepare tasks/<agent-id>/prompt.md + ledger row
+//!   - `prepare`    — orchestrator-facing `AgentInvocation` bundle (ergonomics)
 //!   - `verify`     — run all verify capabilities against agent's return
 //!   - `simulated_merge` — orchestrator-side worktree → apply diff → verify
 //!
@@ -15,6 +16,7 @@
 pub mod capability;
 pub mod compose;
 pub mod gates;
+pub mod prepare;
 pub mod registry;
 pub mod simulated_merge;
 pub mod spawn;
diff --git a/_primitives/_rust/kei-agent-runtime/src/main.rs b/_primitives/_rust/kei-agent-runtime/src/main.rs
index 24ed8ca..b92378e 100644
--- a/_primitives/_rust/kei-agent-runtime/src/main.rs
+++ b/_primitives/_rust/kei-agent-runtime/src/main.rs
@@ -2,7 +2,7 @@
 
 use clap::{Parser, Subcommand};
 use kei_agent_runtime::capability::RunMode;
-use kei_agent_runtime::{compose, spawn, verify};
+use kei_agent_runtime::{compose, prepare, spawn, verify};
 use std::path::PathBuf;
 use std::process::ExitCode;
 
@@ -51,6 +51,16 @@ enum Cmd {
         #[arg(long)]
         kit_root: Option<PathBuf>,
     },
+    /// Assemble everything orchestrator needs to invoke Agent tool.
+    /// Does NOT write tasks/ on disk — inspection helper.
+    Prepare {
+        task: PathBuf,
+        #[arg(long)]
+        kit_root: Option<PathBuf>,
+        /// Output format: human (default) | json | toml
+        #[arg(long, default_value = "human")]
+        format: String,
+    },
 }
 
 fn main() -> ExitCode {
@@ -62,6 +72,35 @@ fn main() -> ExitCode {
             run_verify(task, worktree, kit_root, main_repo, mode)
         }
         Cmd::Run { task, worktree, kit_root } => run_run(task, worktree, kit_root),
+        Cmd::Prepare { task, kit_root, format } => run_prepare(task, kit_root, format),
+    }
+}
+
+fn run_prepare(task_path: PathBuf, kit_root: Option<PathBuf>, format: String) -> ExitCode {
+    let kit = kit_root_or_cwd(kit_root);
+    let task = match spawn::load_task(&task_path) {
+        Ok(t) => t,
+        Err(e) => return err("load task", e),
+    };
+    let inv = match prepare::prepare(&task, &kit) {
+        Ok(i) => i,
+        Err(e) => return err("prepare", e),
+    };
+    let rendered = match format.as_str() {
+        "human" => Ok(prepare::render_human(&inv)),
+        "json" => prepare::render_json(&inv),
+        "toml" => prepare::render_toml(&inv),
+        other => {
+            eprintln!("unknown format '{other}' (expected human|json|toml)");
+            return ExitCode::from(2);
+        }
+    };
+    match rendered {
+        Ok(s) => {
+            print!("{s}");
+            ExitCode::SUCCESS
+        }
+        Err(e) => err("render", e),
     }
 }
 
diff --git a/_primitives/_rust/kei-agent-runtime/src/prepare.rs b/_primitives/_rust/kei-agent-runtime/src/prepare.rs
new file mode 100644
index 0000000..7e18121
--- /dev/null
+++ b/_primitives/_rust/kei-agent-runtime/src/prepare.rs
@@ -0,0 +1,170 @@
+//! Orchestrator-facing wrapper: task.toml → everything needed to invoke
+//! Claude Code's `Agent` tool in a single copy-paste-ready bundle.
+//!
+//! Per RULE 0.13, the orchestrator (main session) owns branch creation,
+//! `isolation: "worktree"` selection, and the actual Agent-tool call. This
+//! module only assembles the arguments — no git, no spawn, no shell.
+//!
+//! Wire: `prepare()` = `compose_prompt()` + role lookup + role→subagent_type
+//! resolution. Deliberately does NOT create `tasks/<id>/` on disk (that is
+//! `spawn::prepare_agent`'s job) so orchestrator can inspect before
+//! committing. The "ledger row" field is a pretty-printed string, not a DB
+//! write — ledger persistence is the orchestrator's step.
+
+use crate::capability::TaskSpec;
+use crate::compose::compose_prompt;
+use anyhow::{anyhow, Context, Result};
+use serde::{Deserialize, Serialize};
+use std::path::Path;
+
+/// Everything the orchestrator needs to hand the Claude `Agent` tool.
+#[derive(Debug, Clone, Serialize)]
+pub struct AgentInvocation {
+    pub agent_id: String,
+    pub role: String,
+    pub prompt: String,
+    pub subagent_type: String,
+    pub isolation: Option<String>,
+    pub description: String,
+    pub verify_command: String,
+    pub ledger_row: String,
+}
+
+/// Assemble an `AgentInvocation` from a parsed task.toml.
+///
+/// Errors if the role is unknown or non-spawnable (points at RULE 0.13).
+pub fn prepare(task: &TaskSpec, kit_root: &Path) -> Result<AgentInvocation> {
+    if task.task.role.is_empty() {
+        return Err(anyhow!("task.role is empty"));
+    }
+    if task.task.agent_id.is_empty() {
+        return Err(anyhow!(
+            "task.agent-id is empty — orchestrator must allocate via kei-ledger"
+        ));
+    }
+    let role_file = load_role_file(kit_root, &task.task.role)?;
+    if !role_file.role.spawnable {
+        return Err(anyhow!(
+            "role '{}' is NOT spawnable (per RULE 0.13 git-ops is \
+             orchestrator-only) — refusing to prepare Agent tool invocation",
+            task.task.role
+        ));
+    }
+    let prompt = compose_prompt(task, kit_root)?;
+    let subagent_type = role_file.role.claude_subagent_type.clone().unwrap_or_else(
+        || default_subagent_type(&task.task.role),
+    );
+    let isolation = default_isolation(&task.task.role);
+    let description = build_description(&task.task.role, &task.task.agent_id);
+    let verify_command = build_verify_command(&task.task.agent_id);
+    let ledger_row = build_ledger_row(task);
+    Ok(AgentInvocation {
+        agent_id: task.task.agent_id.clone(),
+        role: task.task.role.clone(),
+        prompt,
+        subagent_type,
+        isolation,
+        description,
+        verify_command,
+        ledger_row,
+    })
+}
+
+/// Human-readable block — copy into Claude Code's Agent-tool dialog.
+pub fn render_human(inv: &AgentInvocation) -> String {
+    let iso = inv.isolation.as_deref().unwrap_or("<none>");
+    let mut out = String::new();
+    out.push_str("=== AGENT SUBSTRATE v1 — PREPARED SPAWN ===\n");
+    out.push_str(&format!("agent-id: {}\n", inv.agent_id));
+    out.push_str(&format!("subagent_type: {}\n", inv.subagent_type));
+    out.push_str(&format!("isolation: {iso}\n"));
+    out.push_str(&format!("description: {}\n", inv.description));
+    out.push_str("\n--- PROMPT (copy into Agent tool `prompt` param) ---\n");
+    out.push_str(&inv.prompt);
+    if !inv.prompt.ends_with('\n') {
+        out.push('\n');
+    }
+    out.push_str("--- END PROMPT ---\n\n");
+    out.push_str("on return:\n");
+    out.push_str(&format!("  {}\n", inv.verify_command));
+    out.push_str("  (orchestrator harness returns worktree path in the task-notification)\n\n");
+    out.push_str(&format!("ledger: {}\n", inv.ledger_row));
+    out
+}
+
+pub fn render_json(inv: &AgentInvocation) -> Result<String> {
+    serde_json::to_string_pretty(inv).context("serialize AgentInvocation to JSON")
+}
+
+pub fn render_toml(inv: &AgentInvocation) -> Result<String> {
+    toml::to_string_pretty(inv).context("serialize AgentInvocation to TOML")
+}
+
+fn default_isolation(role: &str) -> Option<String> {
+    match role {
+        "edit-local" | "edit-shared" => Some("worktree".into()),
+        _ => None,
+    }
+}
+
+fn default_subagent_type(role: &str) -> String {
+    match role {
+        "edit-local" | "edit-shared" => "code-implementer",
+        "explorer" => "Explore",
+        "read-only" => "critic",
+        _ => "critic",
+    }
+    .into()
+}
+
+fn build_description(role: &str, agent_id: &str) -> String {
+    let short = agent_id.split('-').take(2).collect::<Vec<_>>().join("-");
+    format!("{role} agent {short}")
+}
+
+fn build_verify_command(agent_id: &str) -> String {
+    format!(
+        "kei-agent-runtime verify tasks/{id}/task.toml \
+         --worktree <path-from-harness>",
+        id = agent_id
+    )
+}
+
+fn build_ledger_row(task: &TaskSpec) -> String {
+    let parent = task
+        .task
+        .parent_agent
+        .as_deref()
+        .filter(|s| !s.is_empty())
+        .unwrap_or("none");
+    format!(
+        "running agent-id={} role={} parent={}",
+        task.task.agent_id, task.task.role, parent
+    )
+}
+
+fn load_role_file(kit_root: &Path, role: &str) -> Result<RoleFile> {
+    let path = kit_root.join("_roles").join(format!("{role}.toml"));
+    let text = std::fs::read_to_string(&path)
+        .with_context(|| format!("read role file {}", path.display()))?;
+    toml::from_str::<RoleFile>(&text)
+        .with_context(|| format!("parse role TOML {}", path.display()))
+}
+
+#[derive(Debug, Deserialize)]
+struct RoleFile {
+    #[serde(default)]
+    role: RoleMeta,
+}
+
+#[derive(Debug, Default, Deserialize)]
+struct RoleMeta {
+    #[serde(default = "spawnable_default")]
+    spawnable: bool,
+    #[serde(default, rename = "claude-subagent-type")]
+    claude_subagent_type: Option<String>,
+}
+
+fn spawnable_default() -> bool {
+    true
+}
diff --git a/_primitives/_rust/kei-agent-runtime/tests/prepare_smoke.rs b/_primitives/_rust/kei-agent-runtime/tests/prepare_smoke.rs
new file mode 100644
index 0000000..28e5081
--- /dev/null
+++ b/_primitives/_rust/kei-agent-runtime/tests/prepare_smoke.rs
@@ -0,0 +1,120 @@
+//! Prepare smoke — validates orchestrator-facing wrapper.
+//!
+//! Three fixtures per task spec:
+//!   1. Happy path — valid task.toml → AgentInvocation fully populated
+//!   2. Unknown role → clear error (role lookup fails)
+//!   3. Non-spawnable role (git-ops) → explicit refusal + RULE 0.13 pointer
+
+use kei_agent_runtime::capability::TaskSpec;
+use kei_agent_runtime::prepare::{prepare, render_human};
+use tempfile::TempDir;
+
+fn write_capability(root: &std::path::Path, cat: &str, slug: &str, body: &str) {
+    let dir = root.join("_capabilities").join(cat).join(slug);
+    std::fs::create_dir_all(&dir).unwrap();
+    std::fs::write(dir.join("text.md"), body).unwrap();
+}
+
+fn write_role(root: &std::path::Path, name: &str, toml: &str) {
+    std::fs::create_dir_all(root.join("_roles")).unwrap();
+    std::fs::write(root.join("_roles").join(format!("{name}.toml")), toml).unwrap();
+}
+
+#[test]
+fn happy_path_yields_full_invocation() {
+    let tmp = TempDir::new().unwrap();
+    let root = tmp.path();
+
+    write_capability(root, "policy", "no-git-ops", "## Never git.\n");
+    write_capability(root, "output", "report-format", "## Report fields.\n");
+    write_role(
+        root,
+        "edit-local",
+        r#"
+[role]
+name = "edit-local"
+spawnable = true
+claude-subagent-type = "code-implementer"
+
+[capabilities]
+required = ["policy::no-git-ops", "output::report-format"]
+"#,
+    );
+
+    let mut task = TaskSpec::default();
+    task.task.role = "edit-local".into();
+    task.task.agent_id = "edit-local-forge-abc123".into();
+    task.body.text = "Port kei-forge templating to pure-Rust.".into();
+
+    let inv = prepare(&task, root).expect("prepare should succeed");
+    assert_eq!(inv.agent_id, "edit-local-forge-abc123");
+    assert_eq!(inv.role, "edit-local");
+    assert_eq!(inv.subagent_type, "code-implementer");
+    assert_eq!(inv.isolation.as_deref(), Some("worktree"));
+    assert!(inv.prompt.contains("Never git"));
+    assert!(inv.prompt.contains("Report fields"));
+    assert!(inv.prompt.contains("Port kei-forge templating"));
+    assert!(inv.verify_command.contains("kei-agent-runtime verify"));
+    assert!(inv.verify_command.contains("edit-local-forge-abc123"));
+    assert!(inv.ledger_row.contains("running"));
+    assert!(inv.ledger_row.contains("edit-local"));
+    assert!(inv.ledger_row.contains("parent=none"));
+
+    let human = render_human(&inv);
+    assert!(human.contains("=== AGENT SUBSTRATE v1"));
+    assert!(human.contains("--- PROMPT"));
+    assert!(human.contains("--- END PROMPT"));
+    assert!(human.contains("subagent_type: code-implementer"));
+}
+
+#[test]
+fn unknown_role_errors_clearly() {
+    let tmp = TempDir::new().unwrap();
+    let root = tmp.path();
+
+    let mut task = TaskSpec::default();
+    task.task.role = "does-not-exist".into();
+    task.task.agent_id = "x-1".into();
+
+    let err = prepare(&task, root).expect_err("unknown role must fail");
+    let msg = format!("{err:#}");
+    assert!(
+        msg.contains("does-not-exist") || msg.contains("role"),
+        "error should mention the role or the word 'role': got {msg}"
+    );
+}
+
+#[test]
+fn non_spawnable_role_refused_with_rule_013_pointer() {
+    let tmp = TempDir::new().unwrap();
+    let root = tmp.path();
+
+    write_role(
+        root,
+        "git-ops",
+        r#"
+[role]
+name = "git-ops"
+spawnable = false
+claude-subagent-type = "NOT-SPAWNABLE"
+
+[capabilities]
+required = []
+"#,
+    );
+
+    let mut task = TaskSpec::default();
+    task.task.role = "git-ops".into();
+    task.task.agent_id = "orchestrator-only-1".into();
+
+    let err = prepare(&task, root).expect_err("git-ops must be refused");
+    let msg = format!("{err:#}");
+    assert!(
+        msg.contains("RULE 0.13"),
+        "refusal must cite RULE 0.13: got {msg}"
+    );
+    assert!(
+        msg.contains("spawnable") || msg.contains("orchestrator"),
+        "refusal message should mention spawnable/orchestrator: got {msg}"
+    );
+}
diff --git a/_roles/edit-local.toml b/_roles/edit-local.toml
index 8910296..e7e53dc 100644
--- a/_roles/edit-local.toml
+++ b/_roles/edit-local.toml
@@ -3,6 +3,9 @@ name = "edit-local"
 display-name = "code-implementer (local edit scope)"
 description = "Write code within whitelisted files, run cargo check/test, emit structured report. No git, no workspace-level touches, no dep bumps."
 spawnable = true
+# Default Claude Code subagent_type to hand `prepare` output to.
+# Overridable per-task; see docs/AGENT-SUBSTRATE-SCHEMA.md §Orchestrator ergonomics.
+claude-subagent-type = "code-implementer"
 
 [capabilities]
 # Ordered list — text.md fragments concatenated in this order
diff --git a/_roles/edit-shared.toml b/_roles/edit-shared.toml
index 4621cdc..a627f70 100644
--- a/_roles/edit-shared.toml
+++ b/_roles/edit-shared.toml
@@ -3,6 +3,7 @@ name = "edit-shared"
 display-name = "code-implementer (shared-SSoT edit scope)"
 description = "Same baseline as edit-local, with one relaxed scope entry permitting edits to a task-specified SSoT path (e.g. workspace Cargo.toml, registry file). The relaxation is configured per task via `[scope].files-whitelist` in task.toml."
 spawnable = true
+claude-subagent-type = "code-implementer"
 
 [capabilities]
 # Ordered list — text.md fragments concatenated in this order
diff --git a/_roles/explorer.toml b/_roles/explorer.toml
index 19d6457..30d7c13 100644
--- a/_roles/explorer.toml
+++ b/_roles/explorer.toml
@@ -3,6 +3,7 @@ name = "explorer"
 display-name = "explorer + cargo-check (read-only analyst with build probe)"
 description = "Read-only analyst that may run cargo-family commands for build/test introspection. No edits, no git, no non-cargo shell."
 spawnable = true
+claude-subagent-type = "Explore"
 
 [capabilities]
 # Ordered list — text.md fragments concatenated in this order
diff --git a/_roles/git-ops.toml b/_roles/git-ops.toml
index 4bc49c4..3fc8c31 100644
--- a/_roles/git-ops.toml
+++ b/_roles/git-ops.toml
@@ -3,6 +3,8 @@ name = "git-ops"
 display-name = "git operator (orchestrator-only, NOT spawnable)"
 description = "Documented boundary of git authority. Per RULE 0.13, only the orchestrator (main session) holds git power: branch creation, commit, push, merge, rebase, reset, tag. This role is documented for completeness and is refused by kei-agent-runtime at spawn time."
 spawnable = false
+# Documented for completeness; never consumed because spawnable = false.
+claude-subagent-type = "NOT-SPAWNABLE"
 
 [capabilities]
 # No capability restrictions declared here — this role is never composed into
diff --git a/_roles/read-only.toml b/_roles/read-only.toml
index c235dec..c2eaf4a 100644
--- a/_roles/read-only.toml
+++ b/_roles/read-only.toml
@@ -3,6 +3,9 @@ name = "read-only"
 display-name = "explorer (read-only analyst)"
 description = "Read-only agent: inspects code, emits structured report with severity grades. No shell, no edits, no git."
 spawnable = true
+# Read-only + severity-grade default maps to critic; architect-flavoured tasks
+# should override this per task via claude-subagent-type in task.toml.
+claude-subagent-type = "critic"
 
 [capabilities]
 # Ordered list — text.md fragments concatenated in this order
diff --git a/docs/AGENT-SUBSTRATE-SCHEMA.md b/docs/AGENT-SUBSTRATE-SCHEMA.md
index 0487dc6..44e6873 100644
--- a/docs/AGENT-SUBSTRATE-SCHEMA.md
+++ b/docs/AGENT-SUBSTRATE-SCHEMA.md
@@ -547,6 +547,58 @@ Phase 5 wired the 5 kit-shipped agents to role+task-spec invocation via a new `s
 
 Backward compatibility: the `substrate_role` field is optional. The 7 non-migrated kit agents (`kei-cost-guardian`, `kei-fal-ai-runner`, `kei-infra-implementer`, `kei-ml-implementer`, `kei-ml-researcher`, `kei-modal-runner`, `kei-researcher`) continue to assemble without change; a deferred v0.24 migration wave will promote them. Task-spec examples showing how the orchestrator invokes each migrated agent live under `_templates/task-examples/`.
 
+## Orchestrator ergonomics — `prepare` command
+
+`compose` emits a prompt, `spawn` writes `tasks/<id>/` on disk, `verify` runs on return. Between compose and spawn, the orchestrator needs to invoke Claude Code's `Agent` tool — which lives inside Claude Code, not in Rust. `kei-agent-runtime prepare` bridges that step: it parses a `task.toml` and emits every argument the Agent-tool call needs in one copy-paste-ready block.
+
+```
+kei-agent-runtime prepare <task.toml> [--kit-root .] [--format human|json|toml]
+```
+
+Human output:
+
+```
+=== AGENT SUBSTRATE v1 — PREPARED SPAWN ===
+agent-id: <id>
+subagent_type: <role-derived>
+isolation: worktree
+description: <role> agent <short>
+
+--- PROMPT (copy into Agent tool `prompt` param) ---
+<composed prompt content>
+--- END PROMPT ---
+
+on return:
+  kei-agent-runtime verify tasks/<id>/task.toml --worktree <path-from-harness>
+  (orchestrator harness returns worktree path in the task-notification)
+
+ledger: running agent-id=<id> role=<role> parent=<parent-or-none>
+```
+
+`--format=json` and `--format=toml` emit the same `AgentInvocation` struct for scriptable wrappers (e.g. future `/spawn-agent` Claude Code skill).
+
+### Role → Claude subagent_type mapping
+
+Claude Code's `Agent` tool takes a `subagent_type` string. Roles map to subagent_type via an optional `claude-subagent-type` field on `[role]` in `_roles/<name>.toml`. If unset, the runtime falls back to defaults:
+
+| Role | Default `claude-subagent-type` |
+|---|---|
+| `edit-local`  | `code-implementer` |
+| `edit-shared` | `code-implementer` |
+| `explorer`    | `Explore` |
+| `read-only`   | `critic` (override per-task for architect-flavour reviews) |
+| `git-ops`     | `NOT-SPAWNABLE` (never composed — `spawnable = false`) |
+
+`isolation = "worktree"` is auto-set for `edit-local` and `edit-shared`; other roles default to no isolation.
+
+### Non-spawnable refusal
+
+`prepare` refuses roles with `spawnable = false` and cites RULE 0.13 in the error. `git-ops` is the only shipped example; the refusal keeps "who can do git" boundary visible both in the role manifest AND at invocation time.
+
+### Contract
+
+`prepare` does NOT write to disk (inspection helper) and does NOT touch the ledger DB (the "ledger row" field is a pretty-printed string for the orchestrator to verify before calling `kei-ledger fork`). `spawn` remains the disk-writing step; `prepare` is additive and read-only.
+
 ## Deferred extension candidates (non-breaking post-lock)
 
 Capability atoms NOT in the initial 10 but good follow-up PRs (non-breaking additions during lock window):