refactor(db): extract reminder delivery store

[TheSentinel454]

Current reconstructed head

Exact base: codex/issue-12-allowlist-store at 7ae63f6be2f3f1265b976f37756f3ca0caaffa59
Exact head: codex/issue-13-reminder-store at 9ca2f893f7c23d972cb90c163672b2e5bbbf5e1b

This current head removes crates/buzz-db/tests/store_ownership.rs; no replacement path-sensitive ownership test is introduced. Apart from removing that complete test-file diff, the production patch is byte-for-byte identical to the previously reviewed slice. This remains part of tracker #2 and the #17/#19 acceptance work.

Independent exact-head review from a separate clean Blox workstation found no issues. Current-head evidence passed formatting, strict buzz-db clippy, 111 non-PostgreSQL library tests with 200 PostgreSQL tests ignored, the observability source test, relay consumer compilation, exact ownership/unique-span review checks, and 4 reminder PostgreSQL tests on native PostgreSQL where applicable.

Why

Complete the reminder-delivery slice of tracker #2 and domain issue #13 while keeping event insertion/materialization separate from reminder scheduling. This child stacks on the authentication-allowlist extraction in #6784.

What

• Add a dedicated reminder.rs owner for DueReminder, due-reminder querying, atomic claim/claim-with-stamp/release SQL, Db methods, focused PostgreSQL tests, and datastore spans
• Preserve the existing Db signatures and buzz_db::event::{DueReminder, query_due_reminders, claim_due_reminder, claim_due_reminder_with_stamp, release_due_reminder} paths with compatibility re-exports
• Add the canonical crate-root DueReminder export
• Preserve event-table storage, latest-per-address ordering, archived-community exclusion, claim stamp semantics, and cross-community isolation
• Keep extract_not_before and its four parser tests in event.rs, beside general event insertion materialization

Stack

• Exact base: codex/issue-12-allowlist-store at fa88a64 (#6784)
• Exact head: codex/issue-13-reminder-store at 888627a
• Tracker: buzz-db: break up lib.rs — move impl Db methods to domain modules TheSentinel454/buzz#2
• Domain: buzz-db: extract reminders from event.rs into reminder.rs TheSentinel454/buzz#13
• Test/span acceptance: buzz-db: move lib.rs tests (~4,000 lines) to domain modules TheSentinel454/buzz#17 and buzz-db: consistent #[datastore_span] tracing placement TheSentinel454/buzz#19

Non-goals

• No SQL, schema, ordering, retry, timeout, transaction, or client-visible behavior changes
• No movement of event insertion or not_before materialization out of event.rs
• No reminder scheduler/relay behavior change
• No store traits, domain-handle redesign, broad PgExecutor migration, raw pool accessor, new crate, or directory-wide reorganization
• No changes to, retargeting of, or merge action on parent PRs or PR Add database pressure observability #6700

Risk Assessment

Low. This is a direct ownership move. SQL and bind order are unchanged, public Db and prior event module paths remain compatible, and the moved PostgreSQL tests cover latest-due tenant identity, cross-pod claim exclusion, matching-stamp release, and cross-community isolation.

Blox Verification

Author workstation: buzz-tornquist-issue-2-store-stack (2046520), exact head 52b7bb6cba2a0d09877cc8a1b3a561eb537256da.

• cargo fmt --all --check — passed
• cargo clippy -p buzz-db -p buzz-relay --all-targets -- -D warnings — passed
• Native PostgreSQL: DATABASE_URL=postgres://buzz:…@localhost:5432/buzz cargo test -p buzz-db reminder::tests:: -- --ignored --test-threads=1 — 4 passed
• cargo test -p buzz-relay --lib -- --test-threads=1 — 909 passed, 48 ignored
• git diff --check and commit-time formatting, sadscan, attribution, and sign-off hooks — passed

Independent exact-head review: buzz-tornquist-pr-6787-review (2049679) checked detached head 52b7bb6cba2a0d09877cc8a1b3a561eb537256da over exact merge-base f30633fc37d9b44860db5644418e066a917dc113. No critical, important, or minor findings.

Generated with Codex

Superseded pre-comment restack verification

PR #6700 merged before publication completed. This layer was restacked onto current main through the exact parent named above; the final cumulative tip is 2ddcc8a. Cumulative author gates passed: formatting and diff checks; buzz-db and buzz-relay all-target clippy with -D warnings; DB lib 111 passed / 200 ignored; ownership 22/22; observability 1/1; the full isolated PostgreSQL domain matrix; and relay lib 910 passed / 49 ignored.

• Workstation: buzz-tornquist-pr-6787-final-review (2057624), fresh shallow checkout
• Base: b7347e78843d7b63e3cb383da7cbf5ffc956d4f0
• Head: 35f3b66eae412d4aeea1500c9022681966b14a5f
• Findings: none

Reviewed DueReminder, event-table reminder query/claim/release SQL, Db wrappers, tests, and spans moving to reminder.rs. Existing event-module function paths and crate-root type paths are re-exported. Claim stamps, cross-community isolation, concurrency semantics, and release predicates remain unchanged. General event insertion and extract_not_before remain event-owned, avoiding a reversed dependency.

Verification: format and diff checks passed; buzz-db --all-targets clippy passed with -D warnings; DB lib tests passed (111 passed, 200 PostgreSQL tests ignored); ownership (5/5) and observability (1/1) guards passed; all 4 reminder PostgreSQL lifecycle/isolation tests passed on native PostgreSQL 17 with migrations 1-32 successful; relay lib test target compiled successfully. Final worktree was detached at the exact head and clean.

Complete evidence archive SHA-256: 10e79e8829dc5f0a6adc2dbb6cae565ecbe947d0b328e02073d00173a5fb33c7.

Comment-addressed restack

Review follow-up on #6777 removed only the low-value replaceable ownership source test. This PR was restacked onto its rewritten parent; its production patch is unchanged.

• Exact base: fa88a642a7aa10ce74f8cea692653e50b427f89e
• Exact head: 888627a3d41b72c904d1546fe62492f01bdfdd3e
• Final cumulative tip: 6fa2f104d42c6ba85bdf62e7ccb74ceaf4a84f67
• Per-layer patch-ID and tree audits confirm this PR’s production diff is unchanged from its pre-comment head.
• Cumulative Blox gate: formatting and diff checks; strict buzz-db/buzz-relay Clippy; DB lib 111 passed / 200 ignored; ownership 21/21; observability 1/1; every moved PostgreSQL test; relay lib 910 passed / 49 ignored.
• Independent re-review at this exact head: no findings; fresh exact-parent/head Blox review passed fmt/diff, strict Clippy, DB lib 111 passed / 200 ignored, current ownership/observability guards, 4 reminder PostgreSQL tests, and relay compilation.