feat(core): formalize 5-phase sequential planning workflow

[jerop]

Refactor the planning workflow into a 5-phase sequential process (Requirements, Exploration, Design, Planning, and Approval) to ensure higher-quality implementation strategies and explicit user alignment.

• Introduced "Workflow Rules" for sequential execution, user confirmation, and a "Step Back Protocol".
• Phase 1: Enhance requirements gathering with proactive ambiguity checks and a preference for multiple-choice options.

• Phase 2: Refine exploration to focus on architectural mapping and reusable abstractions.
• Phase 3 (Design): Add a mandatory phase for analyzing alternative approaches and securing user selection before planning.

• Phase 4 (Planning): Require a structured plan document.

• Phase 5: Streamline approval and iteration using exit_plan_mode.
• Update documentation to reflect the formalized 5-phase structure.

Closes #18483
Closes #16857

[gemini-cli]

Hi @jerop, thank you so much for your contribution to Gemini CLI! We really appreciate the time and effort you've put into this.

We're making some updates to our contribution process to improve how we track and review changes. Please take a moment to review our recent discussion post: Improving Our Contribution Process & Introducing New Guidelines.

Key Update: Starting January 26, 2026, the Gemini CLI project will require all pull requests to be associated with an existing issue. Any pull requests not linked to an issue by that date will be automatically closed.

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[gemini-cli]

Hi there! Thank you for your contribution to Gemini CLI.

To improve our contribution process and better track changes, we now require all pull requests to be associated with an existing issue, as announced in our recent discussion and as detailed in our CONTRIBUTING.md.

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[gemini-code-assist]

Summary of Changes

Hello @jerop, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the planning capabilities by formalizing the workflow into a structured, sequential five-phase process. The changes aim to improve the clarity, quality, and user involvement throughout the planning stages, ensuring that implementation strategies are well-thought-out and explicitly approved by the user. This structured approach is designed to reduce ambiguities and improve the overall development outcome.

Highlights

• Formalized 5-Phase Sequential Planning Workflow: The planning workflow has been refactored into a new, explicit 5-phase sequential process: Requirements, Exploration, Design, Planning, and Approval. This aims to ensure higher-quality implementation strategies and explicit user alignment.
• Introduced Workflow Rules: New 'Workflow Rules' have been added, emphasizing sequential execution, mandatory user confirmation before proceeding to the next phase, and a 'Step Back Protocol' for re-evaluating previous assumptions if new information arises.
• Enhanced Requirements Phase: The 'Requirements' phase now includes proactive ambiguity checks, categorization of questions, and a preference for providing multiple-choice options when using the ask_user tool.
• Mandatory Design Phase Added: A new, mandatory 'Design' phase has been introduced. This phase requires identifying and analyzing alternative implementation approaches (or justifying a single canonical approach) and securing explicit user selection before planning proceeds.
• Structured Planning Document: The 'Planning' phase now mandates a structured Markdown document format for the implementation plan, requiring specific H2 headings such as 'Problem Statement', 'Proposed Solution', 'Implementation Plan', 'Verification Plan', 'Risks & Mitigations', and 'Alternatives Considered'.
• Updated Documentation: The plan-mode.md documentation has been updated to reflect the new 5-phase structure, including the addition of the 'Design' phase and renumbering of subsequent phases.

Changelog

• docs/cli/plan-mode.md
  • Updated the documented planning workflow from four to five phases.
  • Inserted a 'Design' phase between 'Exploration' and 'Planning'.
  • Adjusted the numbering of subsequent phases to accommodate the new 'Design' phase.
• packages/core/src/prompts/snippets.ts
  • Added a new 'Workflow Rules' section outlining sequential execution, user confirmation, and a 'Step Back Protocol'.
  • Renamed 'Requirements Understanding' to 'Requirements' and expanded its guidelines to include proactive ambiguity identification and structured questioning.
  • Renamed 'Project Exploration' to 'Exploration' and added guidelines for mapping code paths, identifying reusable patterns, and summarizing findings.
  • Split the original 'Design & Planning' into a distinct 'Design' phase and a 'Planning' phase.
  • The new 'Design' phase mandates identifying multiple approaches (or explaining a single one), documenting pros/cons, and requiring user selection via ask_user.
  • The new 'Planning' phase specifies a pre-requisite of a user-selected approach and defines a strict Markdown document structure with specific H2 headings.
  • Renamed 'Review & Approval' to 'Approval' and updated its description to use EXIT_PLAN_MODE_TOOL_NAME.

Activity

• No human activity has occurred on this pull request yet.

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[github-actions]

Size Change: +1.88 kB (+0.01%)

Total Size: 24.3 MB

Filename	Size	Change
./bundle/gemini.js	24.3 MB	+1.88 kB (+0.01%)

ℹ️ View Unchanged

Filename	Size
./bundle/sandbox-macos-permissive-closed.sb	1.03 kB
./bundle/sandbox-macos-permissive-open.sb	890 B
./bundle/sandbox-macos-permissive-proxied.sb	1.31 kB
./bundle/sandbox-macos-restrictive-closed.sb	3.29 kB
./bundle/sandbox-macos-restrictive-open.sb	3.36 kB
./bundle/sandbox-macos-restrictive-proxied.sb	3.56 kB

_{compressed-size-action}

[gemini-code-assist]

Code Review

This pull request introduces a well-structured 5-phase sequential planning workflow, which is a significant improvement for generating high-quality implementation strategies with explicit user alignment. The documentation and prompt updates are clear and comprehensive. I have one high-severity suggestion to improve prompt clarity for the plan's document structure, ensuring the agent generates correctly formatted plans.