Fix/payment request cancellation lifecycle

[dzdidi]

fix: make Payment Request status the canonical Locks lifecycle contract

Prerequisite and scope

This PR is stacked on latest #3 (feat/lock-payment-draining) at 8d86af67f0a3639284c038bf67bc1faa02688ce0 through explicit merge commit 44ed37886122a201b2d5f73c9578ecabb48f72bd. It preserves both prior #27 head 9a266ef2df6a46c115a99e696fefdb4295bf814b and latest #3 head as direct parents; no rebase or force push was used. Keep this PR based on feat/lock-payment-draining until #3 merges.

PR #3 owns persisted invoice deadlines, immutable Paykit Rust rc56 request terms, replay validation, durable lifecycle projection, required-peer/path intake freshness, Creator-local SDK mutation serialization, same-fence target revalidation, payment observation, and destructive staging-only migration 0007.

This follow-up finalizes one canonical lifecycle boundary for Locks:

• signed POST /payment-requests/status returns separate request_state and payment_state axes;
• response retains invoice_created_at, exact protocol/persisted payment_deadline, confirmations, and amount_matched;
• rejected, canceled, and proposal_expired remain distinct request states;
• accepted/proof-submitted requests with payment_state: expired remain distinct payment-deadline expiry;
• rejected/canceled/expired requests retain factual observed-funds fields;
• RecoveryRequired returns typed 503 unavailable; InvalidConflict returns typed 409 conflict;
• missing, partial, unrelated, or failed required-target intake returns unavailable rather than stale lifecycle state;
• exact terminal response fixtures for Locks are published under docs/fixtures/payment-request-status/ and byte-checked against serializer.

Legacy signed POST /transactions/status remains Bitcoin-only compatibility with closed labels undetected, detected, and confirmed. Payment Request lifecycle no longer widens that old enum.

Dependency and version

• paykit-lib / paykit-sdk: exact released rc56 revision 24162ebbcc703251d8038f2e176d1f4cfb117c6a
• Paykit Server workspace packages: 0.1.0-rc6
• No tag, release, merge, deployment, or migration was performed.

TDD and verification

RED evidence:

• legacy rejected/canceled projection test failed because old code returned cancelled instead of factual confirmed;
• fixture contract test failed to compile until exact Locks JSON fixtures existed.

Reviewer-remediation regression locks passed immediately against existing behavior: PostgreSQL now explicitly proves rejected + undetected retains undetected/0/false, canceled is independently selected as sole winning lifecycle state, and rejected + confirmed remains covered.

Passed locally on exact approved restacked candidate commit 44ed37886122a201b2d5f73c9578ecabb48f72bd (tree af6b0350a789ffc80aad9a0697195b362d108cef):

cargo fmt --all -- --check
cargo check --locked --workspace --all-targets
cargo test --locked -p paykit-server -- --test-threads=1
cargo test --locked -p paykit-server --example paykit-companion-auth -- --test-threads=1
cargo test --locked --workspace --no-run
TEST_DATABASE_URL=postgres://postgres:***@127.0.0.1:35591/postgres cargo test --locked -p paykit-server-e2e -- --test-threads=1
cargo clippy --locked --workspace --all-targets --all-features -- -D warnings
RUSTDOCFLAGS="-D warnings" cargo doc --locked --workspace --no-deps --all-features
git diff --check

PostgreSQL 16 full E2E passed with zero matching temporary databases before and after. Two live external-adapter smoke tests remain ignored by design. Original exact-tree closure review requested the two PostgreSQL status regressions added in 9a266ef; focused independent review approved that remediation. Second independent review reproduced and approved exact restacked commit 44ed37886122a201b2d5f73c9578ecabb48f72bd on latest #3 rc56-tag head 8d86af67f0a3639284c038bf67bc1faa02688ce0, including full Server, companion, PostgreSQL E2E, formatting, locked check, Clippy, rustdoc, dependency, migration, ancestry, and clean-tree gates. GitHub CI results below must be read against exact head 44ed37886122a201b2d5f73c9578ecabb48f72bd.

Out of scope

• Locks repository changes;
• graceful deletion orchestration;
• refunds or late-payment entitlement restoration;
• recurring scheduling;
• compatibility aliases or dual lifecycle endpoints;
• merge, tag, release, deployment, or force push.

[ben-kaufman]

Reviewed the changes relative to #3. No additional material issues found in this PR. The inherited Creator lifecycle refresh issue is tracked on #3 and still needs fixing in the stack.