Extract MCP into codex-mcp crate (#15919)

- Split MCP runtime/server code out of `codex-core` into the new
`codex-mcp` crate. New/moved public structs/types include `McpConfig`,
`McpConnectionManager`, `ToolInfo`, `ToolPluginProvenance`,
`CodexAppsToolsCacheKey`, and the `McpManager` API
(`codex_mcp::mcp::McpManager` plus the `codex_core::mcp::McpManager`
wrapper/shim). New/moved functions include `with_codex_apps_mcp`,
`configured_mcp_servers`, `effective_mcp_servers`,
`collect_mcp_snapshot`, `collect_mcp_snapshot_from_manager`,
`qualified_mcp_tool_name_prefix`, and the MCP auth/skill-dependency
helpers. Why: this creates a focused MCP crate boundary and shrinks
`codex-core` without forcing every consumer to migrate in the same PR.

- Move MCP server config schema and persistence into `codex-config`.
New/moved structs/enums include `AppToolApproval`,
`McpServerToolConfig`, `McpServerConfig`, `RawMcpServerConfig`,
`McpServerTransportConfig`, `McpServerDisabledReason`, and
`codex_config::ConfigEditsBuilder`. New/moved functions include
`load_global_mcp_servers` and
`ConfigEditsBuilder::replace_mcp_servers`/`apply`. Why: MCP TOML
parsing/editing is config ownership, and this keeps config
validation/round-tripping (including per-tool approval overrides and
inline bearer-token rejection) in the config crate instead of
`codex-core`.

- Rewire `codex-core`, app-server, and plugin call sites onto the new
crates. Updated `Config::to_mcp_config(&self, plugins_manager)`,
`codex-rs/core/src/mcp.rs`, `codex-rs/core/src/connectors.rs`,
`codex-rs/core/src/codex.rs`,
`CodexMessageProcessor::list_mcp_server_status_task`, and
`utils/plugins/src/mcp_connector.rs` to build/pass the new MCP
config/runtime types. Why: plugin-provided MCP servers still merge with
user-configured servers, and runtime auth (`CodexAuth`) is threaded into
`with_codex_apps_mcp` / `collect_mcp_snapshot` explicitly so `McpConfig`
stays config-only.

codex-rs/config/src/mcp_edit_tests.rs

@@ -0,0 +1,79 @@
+use super::*;
+use crate::McpServerToolConfig;
+use pretty_assertions::assert_eq;
+use std::collections::HashMap;
+use std::time::SystemTime;
+use std::time::UNIX_EPOCH;
+
+#[tokio::test]
+async fn replace_mcp_servers_serializes_per_tool_approval_overrides() -> anyhow::Result<()> {
+    let unique_suffix = SystemTime::now().duration_since(UNIX_EPOCH)?.as_nanos();
+    let codex_home = std::env::temp_dir().join(format!(
+        "codex-config-mcp-edit-test-{}-{unique_suffix}",
+        std::process::id()
+    ));
+    let servers = BTreeMap::from([(
+        "docs".to_string(),
+        McpServerConfig {
+            transport: McpServerTransportConfig::Stdio {
+                command: "docs-server".to_string(),
+                args: Vec::new(),
+                env: None,
+                env_vars: Vec::new(),
+                cwd: None,
+            },
+            enabled: true,
+            required: false,
+            disabled_reason: None,
+            startup_timeout_sec: None,
+            tool_timeout_sec: None,
+            enabled_tools: None,
+            disabled_tools: None,
+            scopes: None,
+            oauth_resource: None,
+            tools: HashMap::from([
+                (
+                    "search".to_string(),
+                    McpServerToolConfig {
+                        approval_mode: Some(AppToolApproval::Approve),
+                    },
+                ),
+                (
+                    "read".to_string(),
+                    McpServerToolConfig {
+                        approval_mode: Some(AppToolApproval::Prompt),
+                    },
+                ),
+            ]),
+        },
+    )]);
+
+    ConfigEditsBuilder::new(&codex_home)
+        .replace_mcp_servers(&servers)
+        .apply()
+        .await?;
+
+    let config_path = codex_home.join(CONFIG_TOML_FILE);
+    let serialized = std::fs::read_to_string(&config_path)?;
+    assert_eq!(
+        serialized,
+        r#"[mcp_servers.docs]
+command = "docs-server"
+
+[mcp_servers.docs.tools]
+
+[mcp_servers.docs.tools.read]
+approval_mode = "prompt"
+
+[mcp_servers.docs.tools.search]
+approval_mode = "approve"
+"#
+    );
+
+    let loaded = load_global_mcp_servers(&codex_home).await?;
+    assert_eq!(loaded, servers);
+
+    std::fs::remove_dir_all(&codex_home)?;
+
+    Ok(())
+}