fix(recipe): auto-inject summon when instructions use delegate()

[clouatre]

Summary

Recipes with an explicit extensions: block that omits summon lose access to the delegate tool. This was a regression introduced in #6964, which moved delegate from an unconditional builtin into the summon platform extension.

ensure_summon_for_subrecipes only checked for sub_recipes presence. It now also scans recipe.instructions for the string delegate( and injects the summon platform extension when found but absent. A tracing::warn is emitted when auto-injection occurs.

Changes

• crates/goose/src/recipe/mod.rs: extend ensure_summon_for_subrecipes to detect delegate( in instructions and auto-inject summon

Tests

Three unit tests added:

• test_ensure_summon_injected_when_delegate_in_instructions: recipe with explicit empty extensions and delegate( in instructions gets summon injected
• test_ensure_summon_not_duplicated_when_already_present: summon already listed + delegate in instructions stays at exactly one summon entry
• test_ensure_summon_not_injected_without_delegate: recipe without delegate and empty extensions stays empty

Reproduction

Before this fix, a recipe like:

extensions:
  - type: builtin
    name: developer
instructions: |
  Use delegate() to spawn subagents.

would fail with delegate tool not found at runtime.

After this fix, summon is auto-injected and the recipe works as expected.

Fixes #7355

[Copilot]

Pull request overview

This PR fixes a regression from #6964 where recipes with explicit extensions: blocks that omit summon lose access to the delegate() tool. The fix extends the ensure_summon_for_subrecipes function to detect delegate( usage in recipe instructions and auto-inject the summon extension when needed.

Changes:

• Extended ensure_summon_for_subrecipes to detect delegate( in instructions and auto-inject summon platform extension
• Added warning when auto-injection occurs due to delegate usage
• Added three unit tests for delegate detection and summon injection scenarios

[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated 1 comment.

Comments suppressed due to low confidence (1)

crates/goose/src/recipe/mod.rs:267

• ensure_summon_for_subrecipes currently injects extensions = Some(vec![summon]) when uses_delegate and extensions is None, which turns an implicit "use globally-enabled extensions" recipe into an explicit/exclusive extensions list (see resolve_extensions_for_new_session), potentially dropping other enabled extensions and changing runtime behavior; consider only auto-injecting when the recipe had an explicit extensions: block (i.e., self.extensions.is_some()), or merging summon into the resolved enabled extensions instead of replacing them.

        let summon_present = self
            .extensions
            .as_ref()
            .map(|exts| exts.iter().any(|e| e.name() == "summon"))
            .unwrap_or(false);

        if uses_delegate && !summon_present {
            warn!("recipe instructions use 'delegate' but 'summon' extension is not listed; auto-injecting summon");
        }

        let summon = ExtensionConfig::Platform {
            name: "summon".to_string(),
            description: String::new(),
            display_name: None,
            bundled: None,
            available_tools: vec![],
        };
        match &mut self.extensions {
            Some(exts) if !exts.iter().any(|e| e.name() == "summon") => exts.push(summon),
            None => self.extensions = Some(vec![summon]),
            _ => {}