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Referenced by019022024028049

RFD 018: Typed Prompt Routing Enum ​

  • Status: Discussion
  • Category: Design
  • Authors: Jean Mertz git@jeanmertz.com
  • Date: 2026-03-01

Summary ​

This RFD introduces a Prompt enum that codifies all prompt types in JP as typed variants, replacing the current implicit code-path-based distinction between permission prompts, result delivery prompts, and tool questions.

Motivation ​

JP has three kinds of prompts during tool execution:

  1. Permission prompts — "Should I run this tool?" Constructed in ToolPrompter::prompt_permission using PermissionInfo.
  2. Result delivery prompts — "Should I deliver this result?" Constructed in ToolPrompter::prompt_result_confirmation as an inline format string.
  3. Tool questions — "Create backup?" Received as Question from Outcome::NeedsInput.

These are handled by three separate code paths in the coordinator, with no shared type representing "a prompt that needs an answer." This makes it difficult to:

  • Apply consistent routing logic (e.g., a detached fallback policy) across all prompt types.
  • Configure behavior per prompt kind in a unified config schema.
  • Discover which prompt types exist — they are scattered across the prompter, coordinator, and tool executor.
  • Extend the system with new prompt types without duplicating routing logic.

Design ​

The Prompt Enum ​

All prompts are modeled as variants of a Prompt enum. JP-level variants are fully self-describing (their answer type, exclusivity, and config key are derived from the variant). Tool questions are the open-ended catch-all.

rust
enum Prompt {
    /// "Should I execute this tool?" — before tool execution.
    /// Constructed by the coordinator. Tools cannot emit this.
    RunTool {
        tool_name: String,
        tool_source: ToolSource,
    },

    /// "Should I deliver this result to the LLM?" — after execution.
    /// Constructed by the coordinator. Tools cannot emit this.
    DeliverToolResult {
        tool_name: String,
    },

    /// Domain-specific question from a tool — during execution.
    /// Wraps the tool-authored Question from jp_tool::Outcome::NeedsInput.
    ToolQuestion {
        tool_name: String,
        question: Question,
    },
}

The enum carries data, not presentation. It does not define question text or ANSI formatting. The prompter (CLI layer) pattern-matches on the variant and renders the appropriate styled output. This keeps the enum usable by different frontends (terminal, JSON-over-IPC, etc.).

Derived Properties ​

Methods on the enum derive properties from the variant:

rust
impl Prompt {
    /// The expected answer type.
    fn answer_type(&self) -> AnswerType {
        match self {
            Self::RunTool { .. } | Self::DeliverToolResult { .. } => {
                AnswerType::Boolean
            }
            Self::ToolQuestion { question, .. } => {
                question.answer_type.clone()
            }
        }
    }

    /// Whether this prompt can only be answered by a human.
    ///
    /// RunTool and DeliverToolResult are always exclusive — the LLM
    /// cannot meaningfully answer "should I run the tool you just
    /// asked me to run?" Tool questions are non-exclusive by default,
    /// but can be overridden per-question in config.
    fn exclusive(&self) -> bool {
        match self {
            Self::RunTool { .. } | Self::DeliverToolResult { .. } => true,
            Self::ToolQuestion { .. } => false,
        }
    }

    /// Config key for policy lookup (used by RFD 049).
    fn config_key(&self) -> &str {
        match self {
            Self::RunTool { .. } => "run",
            Self::DeliverToolResult { .. } => "deliver",
            Self::ToolQuestion { .. } => "tool",
        }
    }

    /// The tool name associated with this prompt.
    fn tool_name(&self) -> &str {
        match self {
            Self::RunTool { tool_name, .. }
            | Self::DeliverToolResult { tool_name }
            | Self::ToolQuestion { tool_name, .. } => tool_name,
        }
    }
}

Why Each Prompt Has Its Own Type ​

JP-level prompts (RunTool, DeliverToolResult) are defined at the type level, not at the call site. This provides:

  1. Discoverability — one enum, one file. Every prompt type JP can produce is visible in one place.
  2. No duplicates — today the permission question text is constructed in build_permission_question, the result text in prompt_result_confirmation, and tool questions come from Question. Three patterns for the same concept.
  3. Mechanical config mapping — config_key() maps directly to config keys in the detached policy (see RFD 049).
  4. Type-level exclusivity — RunTool and DeliverToolResult are always exclusive because the type says so, not because someone remembered to set a boolean.

Future JP-level prompts (e.g., ConfirmEndConversation, ApproveExpensiveModel) add a variant with its own config_key(), exclusive(), and answer_type(). The routing logic, config cascade, and rendering extend mechanically.

Tool Boundary ​

Tools can only produce Outcome::NeedsInput { question }. The coordinator wraps that into Prompt::ToolQuestion { tool_name, question }. A tool cannot construct RunTool or DeliverToolResult because those variants require data (ToolSource) that only the coordinator has, and the tool's output type (Outcome) does not include them. The type boundary is structural.

Rendering ​

The enum does not define question text. Question text today includes ANSI escapes (tool_name.yellow().bold()), async MCP server resolution, and editor-availability-dependent option lists. This is rendering logic that belongs in the prompter (CLI layer).

The prompter pattern-matches on the variant and builds styled text:

rust
// In ToolPrompter — the rendering layer
fn render_prompt(&self, prompt: &Prompt, mcp_client: &Client) -> String {
    match prompt {
        Prompt::RunTool { tool_name, tool_source } => {
            // ANSI formatting, MCP resolution, source label
        }
        Prompt::DeliverToolResult { tool_name } => {
            format!("Deliver {} result to assistant?", tool_name.yellow().bold())
        }
        Prompt::ToolQuestion { question, .. } => {
            question.text.clone()
        }
    }
}

Different frontends (terminal, TUI, JSON-over-IPC for jp tasks attach) render the same Prompt differently without touching the enum.

Prompt Routing ​

The coordinator constructs a Prompt and passes it to a central routing function. In this RFD, routing preserves existing behavior — TTY detection still drives the decision:

rust
fn route_prompt(prompt: &Prompt, has_client: bool) -> PromptAction {
    if has_client {
        return PromptAction::PromptClient;
    }

    // Current non-TTY behavior, now expressed through the enum.
    match prompt {
        Prompt::RunTool { .. } => PromptAction::AutoApprove,
        Prompt::DeliverToolResult { .. } => PromptAction::AutoDeliver,
        Prompt::ToolQuestion { .. } => PromptAction::LlmInquiry,
    }
}

RFD 049 extends this function with configurable detached policies.

Drawbacks ​

Indirection. Adding an enum layer between the coordinator and the prompter is more abstraction for what currently works as direct function calls. The payoff is in extensibility and config integration, not in immediate simplification.

Migration surface. Refactoring three code paths (prompt_permission, prompt_result_confirmation, prompt_question) to construct and route Prompt variants touches multiple files in the coordinator and prompter.

Alternatives ​

Keep prompt types implicit ​

Continue with the current approach where prompt type is determined by which code path you're in. Rejected because it makes future improvements significantly harder — every new routing policy would need to be implemented in three separate places.

text() method on the Prompt enum ​

Have the enum define the question text directly. Rejected because question text includes ANSI escapes, async MCP server resolution, and editor-availability-dependent options. This is presentation, not data.

exclusive as a boolean field instead of a method ​

Store exclusive as a field on every variant. Rejected because RunTool and DeliverToolResult are inherently exclusive — making it a field would allow constructing an impossible state (RunTool { exclusive: false }). The method encodes the invariant in the type.

Non-Goals ​

  • Detached prompt policy. This RFD introduces the type system; configurable detached policies are proposed in RFD 049.
  • Task model and prompt queuing. See [RFD 020].
  • New prompt variants. This RFD formalizes the existing three prompt types. New variants are future work.

Implementation Plan ​

Phase 1: Add the Prompt enum ​

Define the Prompt enum and its methods. Likely in a new module (e.g., jp_cli::cmd::query::tool::prompt or a shared crate if needed by config).

Can be merged independently. No behavioral changes.

Phase 2: Refactor the coordinator ​

Replace direct PermissionInfo / ResultMode / Question handling in the coordinator with Prompt construction and route_prompt() calls. The prompter receives Prompt variants instead of raw data.

Behavior is unchanged — TTY detection still drives routing. The refactor is purely structural.

Depends on Phase 1.

Phase 3: Refactor the prompter ​

Update ToolPrompter to accept Prompt variants. Consolidate prompt_permission, prompt_result_confirmation, and prompt_question into a pattern-match on the enum. The rendering logic stays in the prompter.

Depends on Phase 2.

References ​