docs: adopt POSEIDON and bootstrap the repository

[AndyD9]

Adopts POSEIDON as the engineering method, repairs the half-finished install
that preceded it, and adapts the kit to this repository.

ADR-0005 accepted by PacoRCS on 2026-08-12 — hardening the existing
application in place, superseding ADR-0002's full rewrite. Ready for review.

Repair

install.sh had deleted 25 tracked documents from the worktree and left an
older duplicate of the kit at the repository root. All deletions were
uncommitted; every file was restored from HEAD and every archive move is
recorded at 100% similarity, so no content changed.

Kept live	Archived to docs/archive/
the five ADRs	roadmap, stack, security, quality, support, docs README
	old templates, tickets T0001–T0005

Bootstrap

Written from an audit of the code plus the owner's answers, never inferred:

• ARCHITECTURE.md — seven boundaries, each citing the file it was read from.
• RULES.md — one section per boundary. Invariants are refusals, seeded
  from scripts/security-check.ps1 and real incidents only. No preventive rules
  were invented.
• VALIDATION.md — commands copied from .github/workflows/, with honest
  manual rows where no check exists.
• SETUP.md, PRODUCT.md, AGENTS.md, CURRENT_STATE.md.
• KNOWN_ISSUES.md — KI-001…KI-015 carried over; KI-016…KI-019 found here.
• LEARNINGS.md — LC-2026-001, LC-2026-002.

ADR-0005 — harden, do not rewrite

ADR-0002 mandated a rewrite in a new repository with fresh history. That never
happened: this is the original repository with legacy/ carved out in place by
fc3316d. The owner's decision is to keep every feature and improve the code
underneath — best practices, smaller files, reliability, security.

ADR-0002 is now Superseded by ADR-0005. KI-008 and KI-016 close with it.

Two contradictions remain open:

1. ADR-0004 pins .NET 10, pnpm 11, TypeScript 6, React 19, Tauri 2.11 and a
   rust-toolchain.toml. Actual: net8.0, npm, TS 5.9.3, React 18.3.1, no
   rust-toolchain.toml. .NET 8 support ends November 2026. Those pins are now
   an upgrade path, one unit per step. → KI-017.
2. dotnet test exits 0 having discovered nothing — no .NET test project
   exists. → KI-004, L1.

What is proven

CURRENT_STATE.md lists no shipped capability. The only executed evidence
is cd app; npm test → 4 files, 11 tests, passing, recorded as a baseline.
That is deliberate: the owner reports the application works, but the repository
cannot yet demonstrate it, and writing a capability table from belief is what
this method exists to prevent.

Validation

Command	Result
cd app; npm test	passed — 4 files, 11 tests
git diff --cached --check	passed on the first commit; on the second it flags one line in the ADR-0002 header, whose two-space hard break matches the four lines around it
caps and placeholders	verified by hand
python3 poseidon/checks/check.py --all --strict-placeholders	blocked by environment

checks: agent mode — not deterministic, no CI gate. python3 is absent, so
check.py runs nowhere, including CI. Installing it restores the gate.

No source file was modified. The version reset to 0.0.1-alpha is deliberately
not in this diff — it is a code change and belongs to the first unit.

🤖 Generated with Claude Code