Move template rendering and themes onto PluginHost (#559)

crates-tauri/yaak-app-client/src/commands.rs

@@ -1,12 +0,0 @@
-use crate::PluginContextExt;
-use crate::error::Result;
-use tauri::{Runtime, State, WebviewWindow};
-use yaak_plugins::events::GetThemesResponse;
-use yaak_plugins::manager::PluginManager;
-
-pub(crate) async fn cmd_get_themes<R: Runtime>(
-    window: WebviewWindow<R>,
-    plugin_manager: State<'_, PluginManager>,
-) -> Result<Vec<GetThemesResponse>> {
-    Ok(plugin_manager.get_themes(&window.plugin_context()).await?)
-}

crates-tauri/yaak-app-client/src/lib.rs

@@ -48,7 +48,6 @@ use yaak_plugins::events::{
     CallWorkspaceActionRequest, Color, FilterResponse, GetFolderActionsResponse,
     GetGrpcRequestActionsResponse, GetHttpAuthenticationConfigResponse,
     GetHttpAuthenticationSummaryResponse, GetHttpRequestActionsResponse,
-    GetTemplateFunctionConfigResponse, GetTemplateFunctionSummaryResponse,
     GetWebsocketRequestActionsResponse, GetWorkspaceActionsResponse, InternalEvent,
     InternalEventPayload, JsonPrimitive, PluginContext, RenderPurpose, ShowToastRequest,
 };
@@ -58,10 +57,9 @@ use yaak_rpc_schema::{AppMetaData, EphemeralHttpResponse};
 use yaak_sse::sse::ServerSentEvent;
 use yaak_tauri_utils::window::WorkspaceWindowTrait;
 use yaak_templates::strip_json_comments::strip_json_comments;
-use yaak_templates::{RenderErrorBehavior, RenderOptions, Tokens, transform_args};
+use yaak_templates::{RenderErrorBehavior, RenderOptions};
 use yaak_tls::find_client_certificate;
 
-mod commands;
 mod encoding;
 mod error;
 mod feedback;
@@ -220,56 +218,6 @@ async fn detect_cli_version_for_binary(program: &str) -> Option<String> {
     Some(parts.next().unwrap_or(line).to_string())
 }
 
-async fn cmd_template_tokens_to_string<R: Runtime>(
-    window: WebviewWindow<R>,
-    app_handle: AppHandle<R>,
-    tokens: Tokens,
-) -> YaakResult<String> {
-    let plugin_manager = Arc::new((*app_handle.state::<PluginManager>()).clone());
-    let encryption_manager = Arc::new((*app_handle.state::<EncryptionManager>()).clone());
-    let cb = PluginTemplateCallback::new(
-        plugin_manager,
-        encryption_manager,
-        &PluginContext::new(Some(window.label().to_string()), window.workspace_id()),
-        RenderPurpose::Preview,
-    );
-    let new_tokens = transform_args(tokens, &cb)?;
-    Ok(new_tokens.to_string())
-}
-
-async fn cmd_render_template<R: Runtime>(
-    window: WebviewWindow<R>,
-    app_handle: AppHandle<R>,
-    template: &str,
-    workspace_id: &str,
-    environment_id: Option<&str>,
-    purpose: Option<RenderPurpose>,
-    ignore_error: Option<bool>,
-) -> YaakResult<String> {
-    let environment_chain =
-        app_handle.db().resolve_environments(workspace_id, None, environment_id)?;
-    let plugin_manager = Arc::new((*app_handle.state::<PluginManager>()).clone());
-    let encryption_manager = Arc::new((*app_handle.state::<EncryptionManager>()).clone());
-    let result = render_template(
-        template,
-        environment_chain,
-        &PluginTemplateCallback::new(
-            plugin_manager,
-            encryption_manager,
-            &PluginContext::new(Some(window.label().to_string()), window.workspace_id()),
-            purpose.unwrap_or(RenderPurpose::Preview),
-        ),
-        &RenderOptions {
-            error_behavior: match ignore_error {
-                Some(true) => RenderErrorBehavior::ReturnEmpty,
-                _ => RenderErrorBehavior::Throw,
-            },
-        },
-    )
-    .await?;
-    Ok(result)
-}
-
 async fn cmd_send_feedback<R: Runtime>(
     app_handle: AppHandle<R>,
     feature: String,
@@ -1160,27 +1108,6 @@ async fn cmd_grpc_request_actions<R: Runtime>(
     Ok(plugin_manager.get_grpc_request_actions(&window.plugin_context()).await?)
 }
 
-async fn cmd_template_function_summaries<R: Runtime>(
-    window: WebviewWindow<R>,
-    plugin_manager: State<'_, PluginManager>,
-) -> YaakResult<Vec<GetTemplateFunctionSummaryResponse>> {
-    let results = plugin_manager.get_template_function_summaries(&window.plugin_context()).await?;
-    Ok(results)
-}
-
-async fn cmd_template_function_config<R: Runtime>(
-    window: WebviewWindow<R>,
-    plugin_manager: State<'_, PluginManager>,
-    function_name: &str,
-    values: HashMap<String, JsonPrimitive>,
-    model: AnyModel,
-    _environment_id: Option<&str>,
-) -> YaakResult<GetTemplateFunctionConfigResponse> {
-    Ok(plugin_manager
-        .get_template_function_config(&window.plugin_context(), function_name, values, model.id())
-        .await?)
-}
-
 async fn cmd_get_http_authentication_summaries<R: Runtime>(
     window: WebviewWindow<R>,
     plugin_manager: State<'_, PluginManager>,

crates-tauri/yaak-app-client/src/render.rs

@@ -1,25 +1,8 @@
-use serde_json::Value;
+//! One import path for rendering, wherever the pieces actually live.
+//!
+//! The request renderers are engine code; the template renderers moved to
+//! `yaak-commands` when the template commands did. Callers in this crate do not
+//! need to track which is which.
+
 pub use yaak::render::{render_grpc_request, render_http_request};
-use yaak_models::models::Environment;
-use yaak_models::render::make_vars_hashmap;
-use yaak_templates::{RenderOptions, TemplateCallback, parse_and_render, render_json_value_raw};
-
-pub async fn render_template<T: TemplateCallback>(
-    template: &str,
-    environment_chain: Vec<Environment>,
-    cb: &T,
-    opt: &RenderOptions,
-) -> yaak_templates::error::Result<String> {
-    let vars = &make_vars_hashmap(environment_chain);
-    parse_and_render(template, vars, cb, &opt).await
-}
-
-pub async fn render_json_value<T: TemplateCallback>(
-    value: Value,
-    environment_chain: Vec<Environment>,
-    cb: &T,
-    opt: &RenderOptions,
-) -> yaak_templates::error::Result<Value> {
-    let vars = &make_vars_hashmap(environment_chain);
-    render_json_value_raw(value, vars, cb, opt).await
-}
+pub use yaak_commands::render::{render_json_value, render_template};

crates-tauri/yaak-app-client/src/rpc_ext.rs

@@ -22,6 +22,7 @@ use crate::updates::YaakUpdater;
 use log::warn;
 use serde::Serialize;
 use tauri::{Manager, Runtime, State, WebviewWindow};
+use std::collections::HashMap;
 use std::sync::Arc;
 use tokio::sync::Mutex;
 use yaak_commands::{Host, PluginHost};
@@ -41,7 +42,7 @@ use yaak_models::models::{
 use yaak_models::query_manager::QueryManager;
 use yaak_models::util::BatchUpsertResult;
 use yaak_plugins::events::{
-    FilterResponse, GetFolderActionsResponse, GetGrpcRequestActionsResponse,
+    FilterResponse, JsonPrimitive, RenderPurpose, GetFolderActionsResponse, GetGrpcRequestActionsResponse,
     GetHttpAuthenticationConfigResponse, GetHttpAuthenticationSummaryResponse,
     GetHttpRequestActionsResponse, GetTemplateFunctionConfigResponse,
     GetTemplateFunctionSummaryResponse, GetThemesResponse, GetWebsocketRequestActionsResponse,
@@ -50,11 +51,13 @@ use yaak_plugins::events::{
 use yaak_plugins::api::{PluginNameVersion, PluginSearchResponse, PluginUpdatesResponse};
 use yaak_plugins::manager::PluginManager;
 use yaak_plugins::native_template_functions::encrypt_secure_template_function;
+use yaak_plugins::template_callback::PluginTemplateCallback;
 use yaak_plugins::plugin_meta::PluginMetadata;
 use yaak_rpc::RpcRouter;
 use yaak_rpc_schema::*;
 use yaak_sse::sse::ServerSentEvent;
 use yaak_sync::sync::SyncOp;
+use yaak_templates::TemplateCallback;
 use yaak_tauri_utils::window::WorkspaceWindowTrait;
 use yaak_ws::WebsocketManager;
 
@@ -122,6 +125,42 @@ impl<R: Runtime> PluginHost for ClientCtx<R> {
         self.window.state::<PluginManager>().resolve_plugins_for_runtime_from_db(plugins).await
     }
 
+    fn template_callback(&self, purpose: RenderPurpose) -> impl TemplateCallback {
+        PluginTemplateCallback::new(
+            Arc::new((*self.window.state::<PluginManager>()).clone()),
+            Arc::new(self.encryption_manager().clone()),
+            &self.plugin_context(),
+            purpose,
+        )
+    }
+
+    async fn template_function_summaries(
+        &self,
+    ) -> yaak_commands::Result<Vec<GetTemplateFunctionSummaryResponse>> {
+        Ok(self
+            .window
+            .state::<PluginManager>()
+            .get_template_function_summaries(&self.plugin_context())
+            .await?)
+    }
+
+    async fn template_function_config(
+        &self,
+        function_name: &str,
+        values: HashMap<String, JsonPrimitive>,
+        model_id: &str,
+    ) -> yaak_commands::Result<GetTemplateFunctionConfigResponse> {
+        Ok(self
+            .window
+            .state::<PluginManager>()
+            .get_template_function_config(&self.plugin_context(), function_name, values, model_id)
+            .await?)
+    }
+
+    async fn themes(&self) -> yaak_commands::Result<Vec<GetThemesResponse>> {
+        Ok(self.window.state::<PluginManager>().get_themes(&self.plugin_context()).await?)
+    }
+
     async fn encrypt_secure_template(&self, template: &str) -> yaak_commands::Result<String> {
         let plugin_manager = Arc::new((*self.window.state::<PluginManager>()).clone());
         let encryption_manager = Arc::new(self.encryption_manager().clone());
@@ -227,11 +266,11 @@ async fn cmd_metadata<R: Runtime>(ctx: ClientCtx<R>, _req: CmdMetadataReq) -> Re
 }
 
 async fn cmd_template_tokens_to_string<R: Runtime>(ctx: ClientCtx<R>, req: CmdTemplateTokensToStringReq) -> Result<String> {
-    Ok(crate::cmd_template_tokens_to_string(ctx.window.clone(), ctx.window.app_handle().clone(), req.tokens).await?)
+    Ok(yaak_commands::templates::cmd_template_tokens_to_string(ctx, req).await?)
 }
 
 async fn cmd_render_template<R: Runtime>(ctx: ClientCtx<R>, req: CmdRenderTemplateReq) -> Result<String> {
-    Ok(crate::cmd_render_template(ctx.window.clone(), ctx.window.app_handle().clone(), &req.template, &req.workspace_id, req.environment_id.as_deref(), req.purpose, req.ignore_error).await?)
+    Ok(yaak_commands::templates::cmd_render_template(ctx, req).await?)
 }
 
 async fn cmd_send_feedback<R: Runtime>(ctx: ClientCtx<R>, req: CmdSendFeedbackReq) -> Result<()> {
@@ -326,12 +365,12 @@ async fn cmd_grpc_request_actions<R: Runtime>(ctx: ClientCtx<R>, _req: CmdGrpcRe
     Ok(crate::cmd_grpc_request_actions(ctx.window.clone(), ctx.window.app_handle().state::<PluginManager>()).await?)
 }
 
-async fn cmd_template_function_summaries<R: Runtime>(ctx: ClientCtx<R>, _req: CmdTemplateFunctionSummariesReq) -> Result<Vec<GetTemplateFunctionSummaryResponse>> {
-    Ok(crate::cmd_template_function_summaries(ctx.window.clone(), ctx.window.app_handle().state::<PluginManager>()).await?)
+async fn cmd_template_function_summaries<R: Runtime>(ctx: ClientCtx<R>, req: CmdTemplateFunctionSummariesReq) -> Result<Vec<GetTemplateFunctionSummaryResponse>> {
+    Ok(yaak_commands::templates::cmd_template_function_summaries(ctx, req).await?)
 }
 
 async fn cmd_template_function_config<R: Runtime>(ctx: ClientCtx<R>, req: CmdTemplateFunctionConfigReq) -> Result<GetTemplateFunctionConfigResponse> {
-    Ok(crate::cmd_template_function_config(ctx.window.clone(), ctx.window.app_handle().state::<PluginManager>(), &req.function_name, req.values, req.model, req.environment_id.as_deref()).await?)
+    Ok(yaak_commands::templates::cmd_template_function_config(ctx, req).await?)
 }
 
 async fn cmd_get_http_authentication_summaries<R: Runtime>(ctx: ClientCtx<R>, _req: CmdGetHttpAuthenticationSummariesReq) -> Result<Vec<GetHttpAuthenticationSummaryResponse>> {
@@ -418,8 +457,8 @@ async fn cmd_secure_template<R: Runtime>(ctx: ClientCtx<R>, req: CmdSecureTempla
     Ok(yaak_commands::encryption::cmd_secure_template(ctx, req).await?)
 }
 
-async fn cmd_get_themes<R: Runtime>(ctx: ClientCtx<R>, _req: CmdGetThemesReq) -> Result<Vec<GetThemesResponse>> {
-    Ok(crate::commands::cmd_get_themes(ctx.window.clone(), ctx.window.app_handle().state::<PluginManager>()).await?)
+async fn cmd_get_themes<R: Runtime>(ctx: ClientCtx<R>, req: CmdGetThemesReq) -> Result<Vec<GetThemesResponse>> {
+    Ok(yaak_commands::templates::cmd_get_themes(ctx, req).await?)
 }
 
 async fn cmd_enable_encryption<R: Runtime>(ctx: ClientCtx<R>, req: CmdEnableEncryptionReq) -> Result<()> {

crates/yaak-commands/src/host.rs

@@ -13,6 +13,7 @@
 //! is anything only a desktop can do — open a native window, run the updater,
 //! show a native dialog — those handlers stay with the desktop.
 
+use std::collections::HashMap;
 use std::future::Future;
 use yaak_core::WorkspaceContext;
 use yaak_crypto::manager::EncryptionManager;
@@ -21,8 +22,12 @@ use yaak_models::client_db::ClientDb;
 use yaak_models::models::Plugin;
 use yaak_models::query_manager::QueryManager;
 use yaak_models::util::UpdateSource;
-use yaak_plugins::events::PluginContext;
+use yaak_plugins::events::{
+    GetTemplateFunctionConfigResponse, GetTemplateFunctionSummaryResponse, GetThemesResponse,
+    JsonPrimitive, PluginContext, RenderPurpose,
+};
 use yaak_plugins::plugin_meta::PluginMetadata;
+use yaak_templates::TemplateCallback;
 
 /// Only `Clone` is required here. `Send`/`Sync`/`'static` are deliberately
 /// *not*: a browser host is single-threaded and its connection pool is an
@@ -106,6 +111,30 @@ pub trait PluginHost: Host {
     /// loaded. A host without a runtime can return them untouched.
     fn resolve_plugins(&self, plugins: Vec<Plugin>) -> impl Future<Output = Vec<Plugin>>;
 
+    /// The template functions this host can run, as a callback the renderer
+    /// drives. This is the *only* thing the plugin runtime uniquely provides to
+    /// a render — the variables come from the environment chain, which is an
+    /// ordinary database read — so handing back the callback keeps the rest of
+    /// rendering shared instead of pushing whole commands behind this trait.
+    fn template_callback(&self, purpose: RenderPurpose) -> impl TemplateCallback;
+
+    /// Every template function the installed plugins expose, for the
+    /// autocomplete menu.
+    fn template_function_summaries(
+        &self,
+    ) -> impl Future<Output = crate::Result<Vec<GetTemplateFunctionSummaryResponse>>>;
+
+    /// The form a template function wants to show for the given values.
+    fn template_function_config(
+        &self,
+        function_name: &str,
+        values: HashMap<String, JsonPrimitive>,
+        model_id: &str,
+    ) -> impl Future<Output = crate::Result<GetTemplateFunctionConfigResponse>>;
+
+    /// Themes contributed by plugins.
+    fn themes(&self) -> impl Future<Output = crate::Result<Vec<GetThemesResponse>>>;
+
     /// Re-encrypt the `secure(...)` values in a template.
     ///
     /// Whole operation rather than its pieces because the encryption is only

crates/yaak-commands/src/lib.rs

@@ -17,7 +17,9 @@ pub mod error;
 pub mod host;
 pub mod models;
 pub mod plugins;
+pub mod render;
 pub mod responses;
+pub mod templates;
 
 pub use error::{Error, Result};
 pub use host::{Host, PluginHost};

crates/yaak-commands/src/render.rs

@@ -0,0 +1,30 @@
+//! Rendering a template against an environment chain.
+//!
+//! The variables come from the chain, the functions come from the host's
+//! template callback. Neither of these knows which host it is running under —
+//! that is the whole point of taking the callback as a parameter.
+
+use serde_json::Value;
+use yaak_models::models::Environment;
+use yaak_models::render::make_vars_hashmap;
+use yaak_templates::{RenderOptions, TemplateCallback, parse_and_render, render_json_value_raw};
+
+pub async fn render_template<T: TemplateCallback>(
+    template: &str,
+    environment_chain: Vec<Environment>,
+    cb: &T,
+    opt: &RenderOptions,
+) -> yaak_templates::error::Result<String> {
+    let vars = &make_vars_hashmap(environment_chain);
+    parse_and_render(template, vars, cb, opt).await
+}
+
+pub async fn render_json_value<T: TemplateCallback>(
+    value: Value,
+    environment_chain: Vec<Environment>,
+    cb: &T,
+    opt: &RenderOptions,
+) -> yaak_templates::error::Result<Value> {
+    let vars = &make_vars_hashmap(environment_chain);
+    render_json_value_raw(value, vars, cb, opt).await
+}

crates/yaak-commands/src/templates.rs

@@ -0,0 +1,67 @@
+//! Templates, the functions plugins put in them, and themes.
+//!
+//! Everything here needs the plugin runtime, but only for the one thing it
+//! uniquely provides: running a template function. Resolving the environment
+//! chain and deciding what a render should do about errors are ordinary work
+//! and stay here, where every host gets them the same.
+
+use crate::error::Result;
+use crate::host::PluginHost;
+use crate::render::render_template;
+use yaak_plugins::events::{
+    GetTemplateFunctionConfigResponse, GetTemplateFunctionSummaryResponse, GetThemesResponse,
+    RenderPurpose,
+};
+use yaak_rpc_schema::*;
+use yaak_templates::{RenderErrorBehavior, RenderOptions, transform_args};
+
+pub async fn cmd_render_template<H: PluginHost>(
+    host: H,
+    req: CmdRenderTemplateReq,
+) -> Result<String> {
+    let environment_chain =
+        host.db().resolve_environments(&req.workspace_id, None, req.environment_id.as_deref())?;
+    let cb = host.template_callback(req.purpose.unwrap_or(RenderPurpose::Preview));
+    let options = RenderOptions {
+        // A preview that throws would show the user an error where they expect
+        // to see the value so far, so callers rendering *into the UI* ask for
+        // empties instead.
+        error_behavior: match req.ignore_error {
+            Some(true) => RenderErrorBehavior::ReturnEmpty,
+            _ => RenderErrorBehavior::Throw,
+        },
+    };
+    Ok(render_template(&req.template, environment_chain, &cb, &options).await?)
+}
+
+/// Render only the *arguments* of a template's function calls, leaving the
+/// calls themselves intact. This is what turns a parsed template back into
+/// something displayable without evaluating it.
+pub async fn cmd_template_tokens_to_string<H: PluginHost>(
+    host: H,
+    req: CmdTemplateTokensToStringReq,
+) -> Result<String> {
+    let cb = host.template_callback(RenderPurpose::Preview);
+    Ok(transform_args(req.tokens, &cb)?.to_string())
+}
+
+pub async fn cmd_template_function_summaries<H: PluginHost>(
+    host: H,
+    _req: CmdTemplateFunctionSummariesReq,
+) -> Result<Vec<GetTemplateFunctionSummaryResponse>> {
+    host.template_function_summaries().await
+}
+
+pub async fn cmd_template_function_config<H: PluginHost>(
+    host: H,
+    req: CmdTemplateFunctionConfigReq,
+) -> Result<GetTemplateFunctionConfigResponse> {
+    host.template_function_config(&req.function_name, req.values, &req.model.id()).await
+}
+
+pub async fn cmd_get_themes<H: PluginHost>(
+    host: H,
+    _req: CmdGetThemesReq,
+) -> Result<Vec<GetThemesResponse>> {
+    host.themes().await
+}

crates/yaak-commands/tests/test_host.rs

@@ -8,6 +8,7 @@
 //! `PluginHost` too, without one, which is only possible because that trait
 //! names operations rather than handing back a manager.
 
+use std::collections::HashMap;
 use std::rc::Rc;
 use std::sync::{Arc, Mutex};
 use tempfile::TempDir;
@@ -15,18 +16,24 @@ use yaak_commands::models::{
     cmd_default_headers, cmd_get_workspace_meta, models_delete, models_upsert,
     models_workspace_models,
 };
+use yaak_commands::templates::cmd_render_template;
 use yaak_commands::{Host, PluginHost};
 use yaak_core::WorkspaceContext;
 use yaak_crypto::manager::EncryptionManager;
 use yaak_models::blob_manager::BlobManager;
-use yaak_models::models::{AnyModel, Plugin, Workspace};
+use yaak_models::models::{AnyModel, Environment, EnvironmentVariable, Plugin, Workspace};
 use yaak_models::query_manager::QueryManager;
 use yaak_models::util::{ModelPayload, UpdateSource};
+use yaak_plugins::events::{
+    GetTemplateFunctionConfigResponse, GetTemplateFunctionSummaryResponse, GetThemesResponse,
+    JsonPrimitive, RenderPurpose,
+};
 use yaak_plugins::plugin_meta::PluginMetadata;
 use yaak_rpc_schema::{
-    CmdDefaultHeadersReq, CmdGetWorkspaceMetaReq, ModelsDeleteReq, ModelsUpsertReq,
-    ModelsWorkspaceModelsReq,
+    CmdDefaultHeadersReq, CmdGetWorkspaceMetaReq, CmdRenderTemplateReq, ModelsDeleteReq,
+    ModelsUpsertReq, ModelsWorkspaceModelsReq,
 };
+use yaak_templates::TemplateCallback;
 
 #[derive(Clone)]
 struct TestHost {
@@ -183,6 +190,32 @@ impl Host for SingleThreadedHost {
     }
 }
 
+/// A template callback with no plugins behind it: variables still resolve,
+/// function calls have nothing to run them. A browser host would put a Worker
+/// round-trip where this returns an error.
+struct NoTemplateFunctions;
+
+impl TemplateCallback for NoTemplateFunctions {
+    async fn run(
+        &self,
+        fn_name: &str,
+        _args: HashMap<String, serde_json::Value>,
+    ) -> yaak_templates::error::Result<String> {
+        Err(yaak_templates::error::Error::RenderError(format!(
+            "no plugin runtime to run {fn_name}()"
+        )))
+    }
+
+    fn transform_arg(
+        &self,
+        _fn_name: &str,
+        _arg_name: &str,
+        arg_value: &str,
+    ) -> yaak_templates::error::Result<String> {
+        Ok(arg_value.to_string())
+    }
+}
+
 /// Answering plugin questions with no plugin runtime behind them. A browser
 /// host would put a `postMessage` round-trip to its Worker where these return
 /// constants; the shape of the trait is what makes either possible.
@@ -204,6 +237,29 @@ impl PluginHost for SingleThreadedHost {
     async fn encrypt_secure_template(&self, _template: &str) -> yaak_commands::Result<String> {
         Err(yaak_commands::Error::Generic("no plugin runtime on this host".into()))
     }
+
+    fn template_callback(&self, _purpose: RenderPurpose) -> impl TemplateCallback {
+        NoTemplateFunctions
+    }
+
+    async fn template_function_summaries(
+        &self,
+    ) -> yaak_commands::Result<Vec<GetTemplateFunctionSummaryResponse>> {
+        Ok(Vec::new())
+    }
+
+    async fn template_function_config(
+        &self,
+        function_name: &str,
+        _values: HashMap<String, JsonPrimitive>,
+        _model_id: &str,
+    ) -> yaak_commands::Result<GetTemplateFunctionConfigResponse> {
+        Err(yaak_commands::Error::Generic(format!("no plugin provides {function_name}()")))
+    }
+
+    async fn themes(&self) -> yaak_commands::Result<Vec<GetThemesResponse>> {
+        Ok(Vec::new())
+    }
 }
 
 #[tokio::test]
@@ -227,6 +283,43 @@ async fn a_single_threaded_host_can_implement_the_trait() {
     .expect("workspace models");
     assert!(json.contains(&id), "the workspace should be in its own bootstrap payload");
 
+    // Rendering, on a host whose template callback has no plugins behind it.
+    // Resolving the environment chain is a database read and the render is
+    // shared code; only the callback came from the host. Rendering a real
+    // variable is what proves the chain was resolved rather than skipped.
+    let environment = host
+        .db()
+        .upsert_environment(
+            &Environment {
+                workspace_id: id.clone(),
+                name: "Test env".to_string(),
+                base: true,
+                variables: vec![EnvironmentVariable {
+                    enabled: true,
+                    name: "greeting".to_string(),
+                    value: "hello".to_string(),
+                    id: None,
+                }],
+                ..Default::default()
+            },
+            &host.update_source(),
+        )
+        .expect("seed environment");
+
+    let rendered = cmd_render_template(
+        host.clone(),
+        CmdRenderTemplateReq {
+            template: "${[ greeting ]} world".to_string(),
+            workspace_id: id.clone(),
+            environment_id: Some(environment.id.clone()),
+            purpose: None,
+            ignore_error: None,
+        },
+    )
+    .await
+    .expect("render");
+    assert_eq!(rendered, "hello world", "the environment chain should have been resolved");
+
     // The delete path too, since it is the one that used to reach for a
     // blocking thread this host does not have.
     let workspace = host.db().get_workspace(&id).expect("get workspace");