docs: codify paykit issuer interoperability

[ovitrif]

Closes #1208

This PR:

1. Codifies the Android Paykit issuer contract aligned with bitkit-ios#719 at 5515aa049223dcfa1f1b0eaf0fe4e8f985e4e562.
2. Validates the exact cross-platform request and endpoint fixtures through Android's production filtering and parsing paths.
3. Adds stable automation identifiers and a regtest journey for the incoming Payment Request flow.

Description

• Keeps Lightning identifiers chain-independent and covers network-specific P2TR, P2WPKH, P2SH, and P2PKH identifiers across Bitcoin, testnet, signet, and regtest.
• Enforces exact lowercase btc and identifier casing, preserves issuer order, removes duplicates, and drops unsupported or wrong-network identifiers.
• Requires endpoint payloads to be JSON objects with a non-empty string value, retaining optional string bounds.
• Uses the byte-identical iOS fixture with SHA-256 934f4be316d589a221ace99683c828ae67ec60d433a06fcacb0d31501e5be300.

Preview

N/A — no user-visible changes.

QA Notes

Manual Tests

• 1. Linked regtest issuer → publish a current btc-regtest-p2wpkh JSON endpoint → send the canonical 100,000-sat one-time request → Payment Requests → Pay: Payment Request Confirm shows 100,000 sats and the issuer as recipient.
• 2. Linked regtest issuer → send an uppercase-asset, wrong-network, or unsupported-identifier fixture: the invalid request is not presented as actionable.

Automated Checks

• PaykitIssuerInteropTest.kt: consumes the exact shared JSON fixture and covers accepted and rejected requests and endpoint payloads across all four networks and four documented on-chain scripts.
• PaymentRequestsScreenTest.kt: verifies the stable Pay and Reject automation identifiers; the connected Pixel 9a run passed 5/5 tests.
• Test coverage consolidated from PublicPaykitRepoTest.kt and PaykitPaymentRequestRepoTest.kt into the canonical fixture suite so one source exercises the real parser and request mapper.
• Local compile, full unit suite, detekt, and dev build passed.

[greptile-apps]

Greptile Summary

The PR codifies and tests Android’s Paykit issuer interoperability contract while adding stable automation identifiers for the incoming Payment Request journey.

• Centralizes endpoint identifier filtering and payload parsing.
• Makes on-chain identifiers network-specific while keeping Lightning identifiers chain-independent.
• Adds shared cross-platform fixtures covering accepted and rejected requests and endpoint payloads.
• Adds Payment Request action and confirmation tags plus regtest journey documentation.

Confidence Score: 5/5

The PR appears safe to merge with no concrete blocking or non-blocking defects identified.

The network-specific identifiers remain aligned across publication, request filtering, SDK endpoint selection, and resolution; endpoint parsing preserves prior semantics, and the new automation tags are exposed through the application’s global Compose resource-ID semantics.

Important Files Changed

Filename	Overview
app/src/main/java/to/bitkit/repositories/PaykitIssuerInterop.kt	Centralizes the canonical Bitcoin asset, network-aware identifier filtering, and strict endpoint payload parsing without introducing a behavioral defect.
app/src/main/java/to/bitkit/repositories/PaykitPaymentRequestRepo.kt	Applies current-network endpoint filtering to incoming payment requests while preserving order and removing duplicates.
app/src/main/java/to/bitkit/repositories/PublicPaykitRepo.kt	Delegates endpoint payload handling to the shared interoperability helper and introduces consistent network-specific on-chain method IDs.
app/src/main/java/to/bitkit/services/PaykitSdkService.kt	Uses the shared canonical asset when constructing Paykit request terms.
app/src/test/java/to/bitkit/repositories/PaykitIssuerInteropTest.kt	Exercises the production request mapper and endpoint parser against fixtures for all supported networks.
app/src/main/java/to/bitkit/ui/screens/paymentrequests/PaymentRequestsScreen.kt	Adds externally usable automation tags to incoming request Pay and Reject actions.
app/src/main/java/to/bitkit/ui/screens/wallets/send/SendConfirmScreen.kt	Adds a stable root automation tag distinguishing Payment Request confirmation from ordinary send confirmation.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[Issuer sends one-time Payment Request] --> B[Validate btc asset, lifecycle, amount, and expiry]
    B --> C[Filter identifiers for current network]
    C --> D{Supported identifier remains?}
    D -->|No| E[Do not present request]
    D -->|Yes| F[Resolve linked issuer endpoint]
    F --> G[Parse JSON object and non-empty value]
    G --> H[Validate invoice or address]
    H --> I[Present incoming request]
    I --> J[Open Payment Request confirmation]

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_{Reviews (1): Last reviewed commit: "test: align paykit issuer fixtures" | Re-trigger Greptile}