🤖 Define architecture, planning, and implementation roles

[taras]

Why

The repository assigns model families to agent roles, but only describes the
Implementor in one sentence and gives the Planner one narrow review instruction.
Architectural review, decision-complete planning and cross-agent continuity are
therefore carried in conversation instead of repository instructions.

What changes

Before:

Agents could identify a default role but could not reconstruct its authority,
workflow, evidence requirements or handoff contract from the repository.

After:

AGENTS.md routes Architect, Planner and Implementor work to separate role
contracts. The contracts define decision ownership, review verdicts, planning
completeness, implementation escalation and a common continuity record.

How it works

task and model fallback → role contract → bounded work → durable handoff record

Explicit task assignment wins. GPT remains the default Planner and acts as the
Architect for architecture, stack and milestone work; Opus remains the default
Implementor. The existing Fabel Problem solver mapping is unchanged.

Review guide

Start with: AGENTS.md under Agent Roles

Then review:

1. .agents/architect.md for product-decision ownership and architecture verdicts
2. .agents/planner.md for decision completeness and Implementor handoffs
3. .agents/implementor.md for implementation authority, escalation and evidence

Look carefully at:

• whether the boundaries allow another agent to continue without granting any
  role authority to silently make product decisions

What must stay true

• Common setup, code, verification and writing rules remain in AGENTS.md and
  apply to every role.
• Material product decisions remain with the user.
• Architecture, planning and implementation can receive independent review.
• GitHub mutation still requires explicit user authorization.

How to verify it

• git diff --check passes.
• Each role link in AGENTS.md resolves to a tracked file.
• The malformed Planner heading and an Planner text are absent.
• No source, test, dependency or executable Markdown file changes.

Scope

Included

• Architect, Planner and Implementor role contracts
• Root role routing and cross-agent continuity requirements

Intentionally unchanged

• Product architecture and specifications
• Model-family defaults other than recognizing GPT architecture tasks
• The existing Fabel Problem solver role
• Runtime behavior, tests and dependencies

Risks and limitations

• Role boundaries are instructions rather than a runtime enforcement mechanism.
• Recovery or rollback: revert this documentation-only commit.

Scope confirmation

• Every changed file supports the purpose described above.
• Unrelated cleanup and formatting changes are excluded.
• Generated or mechanical changes are clearly identified.
• The description matches the final diff and test results.

[github-actions]

PR #398: 🤖 Define architecture, planning, and implementation roles

4 files, +275 / -11

Scope

🟡 Large PR with no linked issue.

Structural

✅ No structural bloat detected.

Slop

✅ Slop indicators look low.

Static Analysis

✅ Oxlint found no issues.

Correctness

No extraneous code patterns detected.