docs: escrow relay API, ADRs, README, testnet e2e and OpenSpec archive (#96)

[moises-cisneros]

Refs #96

Part of the chain that replaces #119, split after its review. Tracker: #122. Regrouped from a first 12 PR split (#133 were folded into this one).

Summary

Documentation only. api.md, ADR-0001 and ADR-0003, the server README, the testnet end to end script and the archived OpenSpec change with its merged specs. Run on Serverpod 4.0.4: create_job 89293b2b…3c9a (ledger 5082571) and fund d255f14a…3b18 (ledger 5082572).

Acceptance criteria

The chain as a whole covers #96; this PR carries its slice (see Scope below).

• The app can create and fund a hire on testnet using only prepare… and submitEscrowCall (proven in the docs PR)
• A signed envelope that differs from its preparation in any field is rejected
• A caller can never prepare or submit for a hire that is not theirs
• A submit… call never throws for chain outcomes
• Each preparation has at most one ChainSubmission

Verification evidence

Docs only. The e2e script is documented in puls3_server/README.md under "End-to-end proof on testnet".

Notes for reviewers

• Review against the parent branch (feat/96-escrow-relay-10-endpoint), not main. The commits are ordered to be read one by one.
• Over the 400 line budget: 2016 authored lines, mostly tests of code that moves funds. Splitting further cuts the unit apart, so it needs size:exception.
• Generated code, migrations and recorded fixtures are excluded from the authored count.

Chain Context

Field	Value
Chain	Escrow relay prepare and submit endpoints (#96)
Tracker PR	#122
Position	4 of 4
Base	feat/96-escrow-relay-10-endpoint
Depends on	#132
Follow-up	None (integrates through the tracker)
Review budget	2016 authored (2016 total) / 400
Starts at	feat/96-escrow-relay-10-endpoint
Ends with	Docs, tool/e2e_relay_testnet.dart, openspec/ archive and specs.

Chain Overview

main
 └── #122 Tracker (draft, no merge)
      └── #126 escrow relay foundations: protocol, config, envelope codec and RPC
           └── #129 persist preparations and prepare unsigned escrow envelopes
                └── #132 submit signed escrow calls and expose the relay in the hire endpoint
                     └── 📍 #134 escrow relay API, ADRs, README, testnet e2e and OpenSpec archive

Scope

• Includes: Docs, tool/e2e_relay_testnet.dart, openspec/ archive and specs.
• Excludes: None: last in the chain.

Autonomy

• CI is expected to pass for this PR branch
• This PR has one deliverable scope
• This PR can be rolled back without unrelated changes
• Tests, docs, or manual verification cover this unit

[TOMOKI977]

Approved. This slice is part of the code I reviewed in full on #119 at b0a4adc (all four lenses; see the review there). I checked that the tip of the chain matches b0a4adc except for the CI fix in .env.example and .gitleaks.toml (and main's #112). The follow-ups listed on #119 apply to the chain as a whole.

[cloudflare-workers-and-pages]

Deploying puls3 with    Cloudflare Pages

Latest commit:	919ffb3
Status:	✅  Deploy successful!
Preview URL:	https://05e4921b.puls3-4lw.pages.dev
Branch Preview URL:	https://feat-96-escrow-relay-12-open.puls3-4lw.pages.dev

View logs