Bug Description

The scheduler's execute_job function panics at runtime when a recipe YAML file contains neither a prompt nor instructions field. The CLI path does not validate recipe content when scheduling — only the cron expression is validated.

Affected Code

File: crates/goose/src/scheduler.rs, lines 781-785

let prompt_text = recipe
    .prompt
    .as_ref()
    .or(recipe.instructions.as_ref())
    .unwrap();   // panics if both are None

Recipe loading (lines 724-735) has no validation:

let recipe: Recipe = {
    let extension = recipe_path.extension()...;
    match extension.as_str() {
        "json" | "jsonl" => serde_json::from_str(&recipe_content)?,
        _ => serde_yaml::from_str(&recipe_content)?,
    }
};
// No call to validate_recipe_template_from_content()

CLI path (crates/goose-cli/src/commands/schedule.rs) only validates cron:

validate_cron_expression(&cron)?;   // only validates cron
// recipe content is NOT parsed or validated

Impact

• A user creates a minimal recipe YAML (e.g., just extensions: and activities: without prompt or instructions)
• goose schedule add accepts it without error
• When the cron job fires, the scheduler thread panics
• The panic is silent — no user-visible error at schedule time, only a crash at execution time
• The validate_prompt_or_instructions function exists in crates/goose/src/recipe/validate_recipe.rs but is never called by the scheduler

Steps to Reproduce

1. Create a recipe file test.yaml:

   extensions:
     - developer
   activities:
     - type: ask

2. Schedule it: goose schedule add --id test --cron "0 * * * *" --recipe test.yaml
3. Wait for the cron to fire (or manually trigger)
4. Observe: thread panic at scheduler.rs:785

Proposed Solution

Add recipe content validation in execute_job after deserialization (line 735), before accessing prompt/instructions:

let recipe: Recipe = serde_yaml::from_str(&recipe_content)?;

// Add validation
if recipe.prompt.is_none() && recipe.instructions.is_none() {
    return Err(anyhow::anyhow!(
        "Recipe must specify at least one of `instructions` or `prompt`"
    ));
}

Or, call the existing validate_recipe_template_from_content function that already performs this check.

Happy to submit a PR for this fix.