Make the default architect prompt create a todo list

[mrubens]

This updates the architect prompt and also fixes #5468

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Important

Updates architect mode prompt to create a todo list, adds isEmpty() utility, and enhances getPromptComponent() and getModeSelection() functions with tests.

• Behavior:
  • Updates architect mode prompt to create a todo list using update_todo_list tool instead of a detailed plan in system-prompt snapshots.
  • Emphasizes creating clear, actionable todo lists over markdown documents.
• Functions:
  • Adds getPromptComponent() in system.ts to filter out empty objects using isEmpty().
  • Updates getModeSelection() in modes.ts to merge prompt components with built-in modes.
• Utilities:
  • Introduces isEmpty() in object.ts to check if an object is empty.
• Tests:
  • Adds tests for getPromptComponent() in get-prompt-component.spec.ts.
  • Adds tests for isEmpty() in object.spec.ts.
  • Adds tests for getModeSelection() with empty prompt components in modes-empty-prompt-component.spec.ts.

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[delve-auditor]

✅ No security or compliance issues detected. Reviewed everything up to 4f31a24.

Security Overview

• 🔎 Scanned files: 19 changed file(s)

Detected Code Changes

Change Type	Relevant files
Enhancement	► prompts/system.ts     Implement smarter partial merging of prompt components ► modes.ts     Update mode selection logic for prompt components ► object.ts     Add isEmpty utility function
Refactor	► usePromptHistory.ts     Improve prompt history navigation ► reminder.ts     Update reminder section formatting

Reply to this PR with @delve-auditor followed by a description of what change you want and we'll auto-submit a change to this PR to implement it.

[delve-auditor]

✅ No security or compliance issues detected. Reviewed everything up to f16946947a32554a354a6854d7bf2a0b96d8f5ae.

Security Overview

• 🔎 Scanned files: 18 changed file(s)

Detected Code Changes

Change Type	Relevant files
Enhancement	► src/core/prompts/system.ts     Add getPromptComponent helper function ► src/utils/object.ts     Add isEmpty utility function ► src/shared/modes.ts     Update architect mode instructions
Bug Fix	► webview-ui/src/components/chat/hooks/usePromptHistory.ts     Fix handling of history navigation with modifiers

Reply to this PR with @delve-auditor followed by a description of what change you want and we'll auto-submit a change to this PR to implement it.

[daniel-lxs]

LGTM.

I noticed in the test case that when a promptComponent only has customInstructions but no roleDefinition, the mode ends up with an empty roleDefinition. Is this intentional? Would it make sense to merge partial promptComponents with the built-in mode defaults, so that missing fields (like roleDefinition) fall back to the built-in values rather than empty strings?