diff --git a/_primitives/_rust/keisei/src/adapters/claude_code.rs b/_primitives/_rust/keisei/src/adapters/claude_code.rs
index bc08638..465c8c9 100644
--- a/_primitives/_rust/keisei/src/adapters/claude_code.rs
+++ b/_primitives/_rust/keisei/src/adapters/claude_code.rs
@@ -1,19 +1,19 @@
 //! Claude Code adapter — writes MCP server entry into
-//! `~/.claude/settings.json`. Config shape merges under
-//! `mcpServers.keisei` so we never clobber unrelated entries.
+//! `~/.claude/settings.json` under `mcpServers.keisei`.
 //!
-//! Detection: `$CWD/.claude/settings.json` exists OR
+//! Detection: `$CWD/.claude/settings.json` is a file OR
 //! `$KEISEI_HOME/.claude` (or `$HOME/.claude`) is a directory.
 //! `$KEISEI_HOME` overrides `$HOME` for tests.
 
 use crate::adapter::ClientAdapter;
+use crate::adapters::jsonmcp::{keisei_entry, load_json_or_empty, merge_named, remove_named};
 use crate::brain::Brain;
 use crate::error::Result;
 use crate::fsx::write_atomic;
-use serde_json::{json, Map, Value};
 use std::path::PathBuf;
 
-pub const MCP_ENTRY_KEY: &str = "keisei";
+pub const PARENT_KEY: &str = "mcpServers";
+pub const ENTRY_KEY: &str = "keisei";
 
 pub struct ClaudeCodeAdapter;
 
@@ -56,7 +56,7 @@ impl ClientAdapter for ClaudeCodeAdapter {
             std::fs::create_dir_all(parent)?;
         }
         let mut doc = load_json_or_empty(&cfg)?;
-        merge_mcp_entry(&mut doc, brain);
+        merge_named(&mut doc, PARENT_KEY, ENTRY_KEY, keisei_entry(brain));
         write_atomic(&cfg, &serde_json::to_string_pretty(&doc)?)
     }
 
@@ -66,7 +66,7 @@ impl ClientAdapter for ClaudeCodeAdapter {
             return Ok(());
         }
         let mut doc = load_json_or_empty(&cfg)?;
-        remove_mcp_entry(&mut doc);
+        remove_named(&mut doc, PARENT_KEY, ENTRY_KEY);
         write_atomic(&cfg, &serde_json::to_string_pretty(&doc)?)
     }
 
@@ -74,54 +74,3 @@ impl ClientAdapter for ClaudeCodeAdapter {
         self.user_config_dir().join("settings.json")
     }
 }
-
-fn load_json_or_empty(cfg: &std::path::Path) -> Result<Value> {
-    if !cfg.is_file() {
-        return Ok(json!({}));
-    }
-    let raw = std::fs::read_to_string(cfg)?;
-    if raw.trim().is_empty() {
-        return Ok(json!({}));
-    }
-    Ok(serde_json::from_str(&raw)?)
-}
-
-fn merge_mcp_entry(doc: &mut Value, brain: &Brain) {
-    if !doc.is_object() {
-        *doc = json!({});
-    }
-    let obj = doc.as_object_mut().expect("doc is object after guard");
-    let servers = obj
-        .entry("mcpServers".to_string())
-        .or_insert_with(|| Value::Object(Map::new()));
-    if !servers.is_object() {
-        *servers = Value::Object(Map::new());
-    }
-    let entry = json!({
-        "command": brain.mcp_server_path().to_string_lossy(),
-        "args": [],
-        "env": {
-            "KEISEI_BRAIN_ROOT": brain.root.to_string_lossy(),
-            "KEISEI_BRAIN_NAME": brain.name(),
-        }
-    });
-    servers
-        .as_object_mut()
-        .expect("servers is object")
-        .insert(MCP_ENTRY_KEY.to_string(), entry);
-}
-
-fn remove_mcp_entry(doc: &mut Value) {
-    if !doc.is_object() {
-        return;
-    }
-    let obj = doc.as_object_mut().expect("doc is object after guard");
-    if let Some(servers) = obj.get_mut("mcpServers") {
-        if let Some(map) = servers.as_object_mut() {
-            map.remove(MCP_ENTRY_KEY);
-            if map.is_empty() {
-                obj.remove("mcpServers");
-            }
-        }
-    }
-}
diff --git a/_primitives/_rust/keisei/src/adapters/continue_adapter.rs b/_primitives/_rust/keisei/src/adapters/continue_adapter.rs
index 31805c4..a52a09b 100644
--- a/_primitives/_rust/keisei/src/adapters/continue_adapter.rs
+++ b/_primitives/_rust/keisei/src/adapters/continue_adapter.rs
@@ -1,27 +1,14 @@
 //! Continue.dev adapter — writes MCP server entry into `~/.continue/`.
 //!
-//! Config path strategy [UNVERIFIED — see note]:
-//!   1. If `~/.continue/config.yaml` exists → YAML mode
-//!   2. Else if `~/.continue/config.json` exists → JSON mode
-//!   3. Else if `~/.continue/` exists → create `config.yaml` fresh
-//!   4. Else `detect()` returns false (graceful)
-//!
-//! Schema (both forms), under top-level `mcpServers`:
+//! Picks YAML if `config.yaml` exists, JSON if `config.json` exists,
+//! else defaults to fresh `config.yaml`. Detection fires on `~/.continue/`
+//! dir. Schema [UNVERIFIED — list-form under `mcpServers`]:
 //! ```yaml
 //! mcpServers:
 //!   - name: keisei
-//!     command: /path/to/kei-mcp-server
+//!     command: ...
 //!     args: []
-//!     env:
-//!       KEISEI_BRAIN_ROOT: /Volumes/Brain1
 //! ```
-//!
-//! NOTE: Continue's exact MCP/plugin schema is [UNVERIFIED] in this
-//! session. The adapter uses a list-form `mcpServers` which matches the
-//! v0.18 prototypes and the Continue `config.yaml` conventions observed
-//! in the public docs. If the live schema diverges, update this module.
-//!
-//! Detach preserves all other config keys and all non-keisei servers.
 
 use crate::adapter::ClientAdapter;
 use crate::brain::Brain;
@@ -63,7 +50,6 @@ impl ContinueAdapter {
         } else if json.is_file() {
             (Form::Json, json)
         } else {
-            // Default for a fresh install: YAML (Continue's preferred form).
             (Form::Yaml, yaml)
         }
     }
@@ -109,9 +95,6 @@ impl ClientAdapter for ContinueAdapter {
     }
 }
 
-/// Load doc as a generic `serde_json::Value`. YAML → Value via serde_yaml,
-/// JSON → Value directly. Unifying on `Value` keeps the merge logic form-
-/// independent.
 fn load_doc(cfg: &std::path::Path, form: Form) -> Result<Value> {
     if !cfg.is_file() {
         return Ok(json!({}));
@@ -120,14 +103,13 @@ fn load_doc(cfg: &std::path::Path, form: Form) -> Result<Value> {
     if raw.trim().is_empty() {
         return Ok(json!({}));
     }
-    let parsed: Value = match form {
+    match form {
         Form::Yaml => serde_yaml::from_str(&raw).map_err(|e| Error::ConfigParseError {
             path: cfg.to_path_buf(),
             reason: e.to_string(),
-        })?,
-        Form::Json => serde_json::from_str(&raw)?,
-    };
-    Ok(parsed)
+        }),
+        Form::Json => Ok(serde_json::from_str(&raw)?),
+    }
 }
 
 fn write_doc(cfg: &std::path::Path, form: Form, doc: &Value) -> Result<()> {
diff --git a/_primitives/_rust/keisei/src/adapters/cursor.rs b/_primitives/_rust/keisei/src/adapters/cursor.rs
index 29ffcaf..6d538ca 100644
--- a/_primitives/_rust/keisei/src/adapters/cursor.rs
+++ b/_primitives/_rust/keisei/src/adapters/cursor.rs
@@ -1,18 +1,19 @@
-//! Cursor adapter — writes MCP server entry to Cursor's MCP config.
+//! Cursor adapter — writes MCP entry under `mcpServers.keisei`.
 //!
-//! Config path: `$CWD/.cursor/mcp.json` if the project-local `.cursor/`
-//! dir exists, else `~/.cursor/mcp.json`. Detection fires if either dir
-//! exists. Schema [UNVERIFIED — matches Claude Desktop MCP convention]:
+//! Path: `$CWD/.cursor/mcp.json` if the project-local `.cursor/` exists,
+//! else `~/.cursor/mcp.json`. Detection fires on either dir. Schema
+//! [UNVERIFIED — matches Claude Desktop MCP convention]:
 //! `{ "mcpServers": { "keisei": { "command": "...", "args": [] } } }`.
 
 use crate::adapter::ClientAdapter;
+use crate::adapters::jsonmcp::{keisei_entry, load_json_or_empty, merge_named, remove_named};
 use crate::brain::Brain;
 use crate::error::Result;
 use crate::fsx::write_atomic;
-use serde_json::{json, Map, Value};
 use std::path::PathBuf;
 
-pub const MCP_ENTRY_KEY: &str = "keisei";
+pub const PARENT_KEY: &str = "mcpServers";
+pub const ENTRY_KEY: &str = "keisei";
 
 pub struct CursorAdapter;
 
@@ -69,7 +70,7 @@ impl ClientAdapter for CursorAdapter {
             std::fs::create_dir_all(parent)?;
         }
         let mut doc = load_json_or_empty(&cfg)?;
-        merge_entry(&mut doc, brain);
+        merge_named(&mut doc, PARENT_KEY, ENTRY_KEY, keisei_entry(brain));
         write_atomic(&cfg, &serde_json::to_string_pretty(&doc)?)
     }
 
@@ -79,7 +80,7 @@ impl ClientAdapter for CursorAdapter {
             return Ok(());
         }
         let mut doc = load_json_or_empty(&cfg)?;
-        remove_entry(&mut doc);
+        remove_named(&mut doc, PARENT_KEY, ENTRY_KEY);
         write_atomic(&cfg, &serde_json::to_string_pretty(&doc)?)
     }
 
@@ -87,54 +88,3 @@ impl ClientAdapter for CursorAdapter {
         self.pick_config_path()
     }
 }
-
-fn load_json_or_empty(cfg: &std::path::Path) -> Result<Value> {
-    if !cfg.is_file() {
-        return Ok(json!({}));
-    }
-    let raw = std::fs::read_to_string(cfg)?;
-    if raw.trim().is_empty() {
-        return Ok(json!({}));
-    }
-    Ok(serde_json::from_str(&raw)?)
-}
-
-fn merge_entry(doc: &mut Value, brain: &Brain) {
-    if !doc.is_object() {
-        *doc = json!({});
-    }
-    let obj = doc.as_object_mut().expect("doc is object after guard");
-    let servers = obj
-        .entry("mcpServers".to_string())
-        .or_insert_with(|| Value::Object(Map::new()));
-    if !servers.is_object() {
-        *servers = Value::Object(Map::new());
-    }
-    let entry = json!({
-        "command": brain.mcp_server_path().to_string_lossy(),
-        "args": [],
-        "env": {
-            "KEISEI_BRAIN_ROOT": brain.root.to_string_lossy(),
-            "KEISEI_BRAIN_NAME": brain.name(),
-        }
-    });
-    servers
-        .as_object_mut()
-        .expect("servers is object")
-        .insert(MCP_ENTRY_KEY.to_string(), entry);
-}
-
-fn remove_entry(doc: &mut Value) {
-    if !doc.is_object() {
-        return;
-    }
-    let obj = doc.as_object_mut().expect("doc is object after guard");
-    if let Some(servers) = obj.get_mut("mcpServers") {
-        if let Some(map) = servers.as_object_mut() {
-            map.remove(MCP_ENTRY_KEY);
-            if map.is_empty() {
-                obj.remove("mcpServers");
-            }
-        }
-    }
-}
diff --git a/_primitives/_rust/keisei/src/adapters/jsonmcp.rs b/_primitives/_rust/keisei/src/adapters/jsonmcp.rs
new file mode 100644
index 0000000..a383206
--- /dev/null
+++ b/_primitives/_rust/keisei/src/adapters/jsonmcp.rs
@@ -0,0 +1,70 @@
+//! Shared JSON-merge helpers for MCP-style adapters (claude-code, cursor,
+//! zed). Same algorithm, different parent/entry keys.
+//!
+//! Constructor Pattern: single responsibility — merge / remove one named
+//! server under one named parent, preserving every other key.
+
+use crate::brain::Brain;
+use crate::error::Result;
+use serde_json::{json, Map, Value};
+
+/// Load `cfg` as JSON, or return empty `{}` if missing/blank. JSON parse
+/// errors propagate via `Error::Json`.
+pub fn load_json_or_empty(cfg: &std::path::Path) -> Result<Value> {
+    if !cfg.is_file() {
+        return Ok(json!({}));
+    }
+    let raw = std::fs::read_to_string(cfg)?;
+    if raw.trim().is_empty() {
+        return Ok(json!({}));
+    }
+    Ok(serde_json::from_str(&raw)?)
+}
+
+/// Build the keisei MCP entry value.
+pub fn keisei_entry(brain: &Brain) -> Value {
+    json!({
+        "command": brain.mcp_server_path().to_string_lossy(),
+        "args": [],
+        "env": {
+            "KEISEI_BRAIN_ROOT": brain.root.to_string_lossy(),
+            "KEISEI_BRAIN_NAME": brain.name(),
+        }
+    })
+}
+
+/// Insert `entry` under `doc[parent_key][entry_key]`, creating both keys
+/// as objects if absent. Existing siblings are preserved.
+pub fn merge_named(doc: &mut Value, parent_key: &str, entry_key: &str, entry: Value) {
+    if !doc.is_object() {
+        *doc = json!({});
+    }
+    let obj = doc.as_object_mut().expect("doc object");
+    let parent = obj
+        .entry(parent_key.to_string())
+        .or_insert_with(|| Value::Object(Map::new()));
+    if !parent.is_object() {
+        *parent = Value::Object(Map::new());
+    }
+    parent
+        .as_object_mut()
+        .expect("parent object")
+        .insert(entry_key.to_string(), entry);
+}
+
+/// Remove `doc[parent_key][entry_key]`. If parent ends up empty, remove
+/// parent too (no vestigial `{}` in the config).
+pub fn remove_named(doc: &mut Value, parent_key: &str, entry_key: &str) {
+    if !doc.is_object() {
+        return;
+    }
+    let obj = doc.as_object_mut().expect("doc object");
+    if let Some(parent) = obj.get_mut(parent_key) {
+        if let Some(map) = parent.as_object_mut() {
+            map.remove(entry_key);
+            if map.is_empty() {
+                obj.remove(parent_key);
+            }
+        }
+    }
+}
diff --git a/_primitives/_rust/keisei/src/adapters/mod.rs b/_primitives/_rust/keisei/src/adapters/mod.rs
index 8bdf00f..45db347 100644
--- a/_primitives/_rust/keisei/src/adapters/mod.rs
+++ b/_primitives/_rust/keisei/src/adapters/mod.rs
@@ -1,9 +1,11 @@
 //! Concrete `ClientAdapter` implementations, one file per client.
 //!
 //! Constructor Pattern: this file is the module declaration hub only —
-//! no logic lives here. Each adapter owns its own file.
+//! no logic lives here. `jsonmcp` owns the shared JSON merge helpers
+//! used by every JSON-keyed adapter (claude-code, cursor, zed).
 
 pub mod claude_code;
 pub mod continue_adapter;
 pub mod cursor;
+pub mod jsonmcp;
 pub mod zed;
diff --git a/_primitives/_rust/keisei/src/adapters/zed.rs b/_primitives/_rust/keisei/src/adapters/zed.rs
index 8a16db5..e915384 100644
--- a/_primitives/_rust/keisei/src/adapters/zed.rs
+++ b/_primitives/_rust/keisei/src/adapters/zed.rs
@@ -1,40 +1,20 @@
-//! Zed adapter — writes MCP/context-server entry into Zed settings.
+//! Zed adapter — writes context-server entry under `context_servers.keisei`.
 //!
-//! Config path [UNVERIFIED for exact schema key-name]:
-//!   - macOS:   `~/Library/Application Support/Zed/settings.json`
-//!   - Linux:   `~/.config/zed/settings.json`
-//!   - Windows: not supported in this adapter (Zed Windows is preview)
-//!
-//! Schema (under a top-level `context_servers` object):
-//! ```json
-//! {
-//!   "context_servers": {
-//!     "keisei": {
-//!       "command": "/path/to/kei-mcp-server",
-//!       "args": [],
-//!       "env": { "KEISEI_BRAIN_ROOT": "..." }
-//!     }
-//!   }
-//! }
-//! ```
-//!
-//! NOTE: Zed's `context_servers` key is the documented extension point for
-//! MCP at time of writing — but the full schema (arg handling,
-//! environment) is [UNVERIFIED] in this session. If a future Zed release
-//! diverges, update this module.
-//!
-//! Detach preserves all other settings and all non-keisei context servers.
-//! If the settings file is not valid JSON (Zed historically permitted
-//! JSONC / comments), attach degrades gracefully by returning
-//! `ConfigParseError` — the user can then switch to manual config.
+//! Paths: `~/Library/Application Support/Zed/settings.json` on macOS,
+//! `~/.config/zed/settings.json` on Linux. Detection fires on the
+//! platform settings dir. Schema [UNVERIFIED]:
+//! `{ "context_servers": { "keisei": { "command": "...", "args": [] } } }`.
+//! Invalid JSON (e.g. JSONC with comments) → `ConfigParseError`.
 
 use crate::adapter::ClientAdapter;
+use crate::adapters::jsonmcp::{keisei_entry, merge_named, remove_named};
 use crate::brain::Brain;
 use crate::error::{Error, Result};
 use crate::fsx::write_atomic;
-use serde_json::{json, Map, Value};
+use serde_json::{json, Value};
 use std::path::PathBuf;
 
+pub const PARENT_KEY: &str = "context_servers";
 pub const ENTRY_KEY: &str = "keisei";
 
 pub struct ZedAdapter;
@@ -56,10 +36,6 @@ impl ZedAdapter {
             base.join(".config/zed")
         }
     }
-
-    fn settings_file(&self) -> PathBuf {
-        self.settings_dir().join("settings.json")
-    }
 }
 
 impl Default for ZedAdapter {
@@ -82,10 +58,9 @@ impl ClientAdapter for ZedAdapter {
         if let Some(parent) = cfg.parent() {
             std::fs::create_dir_all(parent)?;
         }
-        let mut doc = load_json_or_empty(&cfg)?;
-        merge_entry(&mut doc, brain);
-        write_atomic(&cfg, &serde_json::to_string_pretty(&doc)?)?;
-        Ok(())
+        let mut doc = load_strict_json(&cfg)?;
+        merge_named(&mut doc, PARENT_KEY, ENTRY_KEY, keisei_entry(brain));
+        write_atomic(&cfg, &serde_json::to_string_pretty(&doc)?)
     }
 
     fn detach(&self) -> Result<()> {
@@ -93,18 +68,19 @@ impl ClientAdapter for ZedAdapter {
         if !cfg.is_file() {
             return Ok(());
         }
-        let mut doc = load_json_or_empty(&cfg)?;
-        remove_entry(&mut doc);
-        write_atomic(&cfg, &serde_json::to_string_pretty(&doc)?)?;
-        Ok(())
+        let mut doc = load_strict_json(&cfg)?;
+        remove_named(&mut doc, PARENT_KEY, ENTRY_KEY);
+        write_atomic(&cfg, &serde_json::to_string_pretty(&doc)?)
     }
 
     fn config_path(&self) -> PathBuf {
-        self.settings_file()
+        self.settings_dir().join("settings.json")
     }
 }
 
-fn load_json_or_empty(cfg: &std::path::Path) -> Result<Value> {
+/// Zed historically permitted JSONC. We require strict JSON and surface a
+/// `ConfigParseError` pointing at the file if the user has comments.
+fn load_strict_json(cfg: &std::path::Path) -> Result<Value> {
     if !cfg.is_file() {
         return Ok(json!({}));
     }
@@ -117,43 +93,3 @@ fn load_json_or_empty(cfg: &std::path::Path) -> Result<Value> {
         reason: e.to_string(),
     })
 }
-
-fn merge_entry(doc: &mut Value, brain: &Brain) {
-    if !doc.is_object() {
-        *doc = json!({});
-    }
-    let obj = doc.as_object_mut().expect("doc is object after guard");
-    let servers = obj
-        .entry("context_servers".to_string())
-        .or_insert_with(|| Value::Object(Map::new()));
-    if !servers.is_object() {
-        *servers = Value::Object(Map::new());
-    }
-    let entry = json!({
-        "command": brain.mcp_server_path().to_string_lossy(),
-        "args": [],
-        "env": {
-            "KEISEI_BRAIN_ROOT": brain.root.to_string_lossy(),
-            "KEISEI_BRAIN_NAME": brain.name(),
-        }
-    });
-    servers
-        .as_object_mut()
-        .expect("servers is object")
-        .insert(ENTRY_KEY.to_string(), entry);
-}
-
-fn remove_entry(doc: &mut Value) {
-    if !doc.is_object() {
-        return;
-    }
-    let obj = doc.as_object_mut().expect("doc is object after guard");
-    if let Some(servers) = obj.get_mut("context_servers") {
-        if let Some(map) = servers.as_object_mut() {
-            map.remove(ENTRY_KEY);
-            if map.is_empty() {
-                obj.remove("context_servers");
-            }
-        }
-    }
-}
diff --git a/_primitives/_rust/keisei/src/error.rs b/_primitives/_rust/keisei/src/error.rs
index 071b6c5..9879ee3 100644
--- a/_primitives/_rust/keisei/src/error.rs
+++ b/_primitives/_rust/keisei/src/error.rs
@@ -23,6 +23,7 @@ pub enum Error {
     NotAttached,
 
     #[error("adapter '{client}' failed: {reason}")]
+    #[allow(dead_code)] // surfaced by mount/detach orchestration; reserved for library consumers
     AdapterFailed { client: String, reason: String },
 
     #[error("config parse error at {path}: {reason}")]
diff --git a/_primitives/_rust/keisei/src/list.rs b/_primitives/_rust/keisei/src/list.rs
index de52a86..a875543 100644
--- a/_primitives/_rust/keisei/src/list.rs
+++ b/_primitives/_rust/keisei/src/list.rs
@@ -27,29 +27,11 @@ struct Row {
 }
 
 fn print_table(rows: &[Row]) {
-    let name_w = header_or_max(rows, "adapter", |r| r.name.len());
-    let det_w = "detected".len();
-    println!(
-        "{:<name_w$}  {:<det_w$}  config_path",
-        "adapter",
-        "detected",
-        name_w = name_w,
-        det_w = det_w
-    );
-    println!("{:<name_w$}  {:<det_w$}  {}", "-------", "--------", "-----------", name_w = name_w, det_w = det_w);
+    let name_w = rows.iter().map(|r| r.name.len()).max().unwrap_or(0).max(7);
+    println!("{:<w1$}  detected  config_path", "adapter", w1 = name_w);
+    println!("{:<w1$}  --------  -----------", "-------", w1 = name_w);
     for r in rows {
-        let mark = if r.detected { "yes" } else { "no" };
-        println!(
-            "{:<name_w$}  {:<det_w$}  {}",
-            r.name,
-            mark,
-            r.config_path,
-            name_w = name_w,
-            det_w = det_w
-        );
+        let mark = if r.detected { "yes     " } else { "no      " };
+        println!("{:<w1$}  {}  {}", r.name, mark, r.config_path, w1 = name_w);
     }
 }
-
-fn header_or_max<F: Fn(&Row) -> usize>(rows: &[Row], header: &str, f: F) -> usize {
-    rows.iter().map(f).max().unwrap_or(0).max(header.len())
-}