Implementation Planning

Implementation Planning Skill

Standard workflow only. If task_complexity is simple and workflow mode is Express, do not activate this skill. Simple tasks use the Express workflow, which does not activate implementation-planning. Return to the Express Workflow section.

Activate this skill during Phase 2 of Maestro orchestration, after the design document has been approved. This skill provides the methodology for generating detailed, actionable implementation plans that map directly to subagent assignments.

Codebase Grounding

Do not generate an implementation plan from guesses about the repository.

Use the built-in codebase_investigator before phase decomposition when:

• The task modifies an existing codebase
• File ownership, integration points, or validation commands are still unclear after reading the approved design
• Parallelization decisions depend on understanding current module boundaries or likely file overlap

Ask the investigator for:

• The modules and files most likely to change
• Existing architectural boundaries and conventions the plan must preserve
• Integration seams, dependencies, and shared ownership hotspots
• Validation commands and test entry points already used by the project
• Parallelization or conflict risks that should prevent batching

Skip the investigator only for greenfield tasks, documentation-only work, or plans where the current turn already established the relevant repo structure from direct reads.

Reuse investigator findings directly in the implementation plan:

• File inventories should reflect real candidate paths, not placeholders
• Validation criteria should prefer repo-native commands the investigator surfaced
• Parallel batches should account for actual ownership overlap and conflict risk

Plan Generation Methodology

Input Analysis

Before generating the plan, thoroughly analyze the approved design document for:

• Read task_complexity from the approved design document's frontmatter. Apply phase count guidance and domain analysis scaling accordingly. Record task_complexity in implementation plan frontmatter.
• Components and their responsibilities
• Interfaces and contracts between components
• Data models and their relationships
• External dependencies and integrations
• Technology stack decisions
• Quality requirements that influence implementation order

Phase Decomposition

Break the implementation into phases following these principles:

1. Foundation First: Infrastructure, configuration, and shared types/interfaces come first
2. Dependencies Flow Downward: A phase can only depend on phases with lower IDs
3. Single Responsibility: Each phase delivers a cohesive unit of functionality
4. Agent Alignment: Each phase maps to one or two agent specializations
5. Agent Capability Match: Verify the assigned agent's tool tier supports the phase deliverables (see compatibility check below)
6. Testability: Each phase should be independently validatable

Phase Ordering Strategy

Layer 1: Foundation (types, interfaces, configuration)
    |
Layer 2: Core Domain (business logic, data models)
    |
Layer 3: Infrastructure (database, external services, API layer)
    |
Layer 4: Integration (connecting components, middleware)
    |
Layer 5: Quality (testing, security review, performance)
    |
Layer 6: Documentation & Polish

Agent-Deliverable Compatibility Check

Before finalizing agent assignments, verify each phase's agent can deliver its requirements:

Phase Count Guidance

Scale decomposition granularity to task_complexity (read from design document frontmatter):

• simple: 1-3 phases. Prefer single-phase execution when feasible. Combine foundation + implementation. Skip separate documentation/polish phases.
• medium: 3-5 phases. Use the layer model but combine Quality and Documentation into the final implementation phase where practical.
• complex: No phase count cap. Full layer decomposition strategy applies.

Parallelization Identification

Phases can run in parallel when:

• They have no shared file dependencies (no overlapping files_created or files_modified)
• They are at the same dependency depth (same layer)
• They do not share data model ownership
• Their validation can run independently

Mark parallel-eligible phases with parallel: true and group them into execution batches.

Implementation Detail Requirements

Per-Phase Specification

Each phase in the plan must include:

Objective

A clear, measurable statement of what this phase delivers.

Agent Assignment

Which agent(s) execute this phase, with rationale for selection.

Files to Create

For each new file:

• Full relative path from project root
• Purpose and responsibility
• Key interfaces, classes, or functions to define
• Complete type signatures for public APIs

Files to Modify

For each existing file:

• Full relative path from project root
• Specific changes required and why
• Expected before/after for critical sections

Implementation Details

Provide sufficient detail for the assigned agent to execute without ambiguity:

• Interface definitions with complete type signatures
• Base class contracts with abstract method signatures
• Dependency injection patterns and registration points
• Error handling strategy (error types, propagation, recovery)
• Configuration requirements (environment variables, config files)

Validation Criteria

Specific commands to run and expected outcomes:

• Build/compile commands
• Lint/format checks
• Unit test commands
• Integration test commands (if applicable)
• Manual verification steps (if applicable)

Dependencies

• blocked_by: Phase IDs that must complete before this phase starts
• blocks: Phase IDs that cannot start until this phase completes

Dependency Minimization

List only direct blockers in blocked_by. Do not include transitive dependencies — they inflate dependency depth and prevent parallelism.

Anti-pattern (over-specified):

• Phase 2: blocked_by: [1]
• Phase 3: blocked_by: [1, 2] — Phase 1 is redundant, already reachable via Phase 2
• Phase 4: blocked_by: [1, 2, 3] — Phases 1, 2 are redundant

Result: depths 0, 1, 2, 3 — zero parallel phases.

Correct (minimized):

• Phase 2: blocked_by: [1]
• Phase 3: blocked_by: [1] — Only needs Phase 1 output, not Phase 2
• Phase 4: blocked_by: [2, 3] — Needs both done

Result: depths 0, 1, 2 — Phases 2 and 3 run in parallel at depth 1.

Ask for each dependency: "Does this phase truly need the output of that specific phase, or is it transitively covered?"

If validate_plan is available, review its parallelization_profile and redundant_dependency warnings before presenting the plan. Revise blocked_by to eliminate redundancies when possible.

Agent Assignment Criteria

Matching Tasks to Agents

Assignment Rules

1. Match the primary task domain to the agent specialization
2. Consider tool requirements — does the task need shell access? Write access?
3. For parallel phases, assign non-overlapping file ownership to each agent
4. Prefer single-agent phases for clarity; use multi-agent only when distinct specializations are needed
5. Never assign more files to an agent than it can handle within its max_turns limit

Token Budget Estimation

Estimate token consumption per phase based on:

• Number of files to read (input tokens)
• Complexity of output expected (output tokens)
• Agent's max_turns limit as upper bound
• Historical averages: ~500 input tokens per file read, ~200 output tokens per file written

Cost Estimation

Per-Phase Cost Factors

• Model tier: Pro agents ($0.01/1K input, ~$0.04/1K output) vs Flash agents ($0.001/1K input, ~$0.004/1K output)
• Input complexity: Number of files read, average file size, context from previous phases
• Output complexity: Lines of code generated, number of files created/modified
• Retry budget: Add 50% buffer per phase for potential retries (max 2 retries)

Estimation Formula

Phase Cost = (input_tokens × input_rate + output_tokens × output_rate) × retry_multiplier

Where:

• input_tokens = files_to_read × 500 + context_tokens
• output_tokens = files_to_write × 200 + validation_output
• retry_multiplier = 1.5 (accounts for up to 2 retries)

Plan-Level Cost Summary

Include this table in every implementation plan:

Plan Document Generation

Output Location

During Plan Mode, write_file is restricted to .md files within ~/.gemini/tmp/<project>/plans/ (where <project> is the CLI's internal project hash). Write the implementation plan there first, then copy to the project archive after approval:

1. During Plan Mode (writable): ~/.gemini/tmp/<project>/plans/YYYY-MM-DD-<topic-slug>-impl-plan.md
2. After approval (permanent reference): <state_dir>/plans/YYYY-MM-DD-<topic-slug>-impl-plan.md (<state_dir> resolves from MAESTRO_STATE_DIR)

The exit_plan_mode tool validates that plan_path is within the project's temp plans directory. Always pass the tmp-directory path.

Document Structure

Use the implementation plan template from templates/implementation-plan.md.

Required Sections

1. Plan Overview: Summary of total phases, agents involved, estimated effort
2. Dependency Graph: Visual representation showing phase dependencies and parallel opportunities
3. Execution Strategy Table: Stage-by-stage breakdown with agent assignments and execution mode
4. Phase Details: Full specification for each phase (objective, agent, files, details, validation, dependencies)
5. File Inventory: Complete table mapping every file to its phase and purpose
6. Risk Classification: Per-phase risk assessment (LOW/MEDIUM/HIGH) with rationale
7. Execution Profile: Summary of parallel vs sequential characteristics to inform mode selection:

   Execution Profile:
   - Total phases: [N]
   - Parallelizable phases: [M] (in [B] batches)
   - Sequential-only phases: [S]
   - Estimated parallel wall time: [time estimate based on batch execution]
   - Estimated sequential wall time: [time estimate based on serial execution]
   
   Note: Native parallel execution currently runs agents in autonomous mode.
   All tool calls are auto-approved without user confirmation.
   

Completion Criteria

The implementation plan is complete when:

• Every component from the design document maps to at least one phase
• All phase dependencies are acyclic (no circular dependencies)
• Parallel opportunities are identified and marked
• Each phase has clear validation criteria
• File ownership is non-overlapping for parallel phases
• The user has given explicit approval of the complete plan

Before presenting the plan for approval, check whether validate_plan appears in your available tools. If it does, call it with the plan structure and task_complexity to verify phase count constraints, file ownership, acyclic dependencies, and agent validity. If it does not, self-check against the phase count limits above.

Post-Generation

After writing the implementation plan:

1. Confirm the file path to the user
2. Present the dependency graph and execution strategy
3. Highlight parallel execution opportunities
4. Provide token budget estimates
5. Call exit_plan_mode with plan_path set to the tmp-directory path (~/.gemini/tmp/<project>/plans/...) to present the plan for user approval
6. After approval, copy the plan to <state_dir>/plans/YYYY-MM-DD-<slug>-impl-plan.md as a permanent project reference
7. Ask if the user is ready to proceed to execution (Phase 3)
8. Upon approval, create the session state file via the session-management skill

Converted and distributed by TomeVault — claim your Tome and manage your conversions.