refactor(db): move user and DM store ownership

[TheSentinel454]

Current reconstructed head

Exact base: codex/issue-2-feed-store at 31f52ef39eb42107a1d593f221ff9894a38ccb39
Exact head: codex/issue-2-user-dm-store at 4664593b6f5f90394bc0d2432b26822dbede9c44

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 8 user PostgreSQL tests and 4 non-PostgreSQL DM tests on native PostgreSQL where applicable.

Why

Continue tracker #2 by completing user and direct-message persistence ownership. The user and DM SQL, records, helpers, and focused tests already lived in user.rs and dm.rs; this child moves the remaining Db APIs and datastore spans out of lib.rs so each domain has one implementation owner. This PR stacks on #6794.

What

• Move all nine user-facing Db APIs and their datastore spans into user.rs
• Move all seven direct-message Db APIs and their datastore spans into dm.rs
• Preserve every public Db method signature and existing crate-root/module exports
• Keep user SQL, profile/search records, row handling, and focused tests in user.rs
• Keep DM SQL, participant/channel records, hashing helpers, and focused tests in dm.rs
• Keep runtime read routing and its proofs/tests in lib.rs
• Retain the existing fixed local-only PostgreSQL test URL with the repository-standard inline sadscan suppression required after its line moved

Stack

• Exact base: codex/issue-2-feed-store at 3062146 (#6794)
• Exact head: codex/issue-2-user-dm-store at d6abdf9
• Tracker: buzz-db: break up lib.rs — move impl Db methods to domain modules TheSentinel454/buzz#2
• Domain issue: none; this is a remaining user/DM slice identified by the extraction ledger
• 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, locking, transaction, retry, timeout, pagination, hashing, visibility, or client-visible behavior changes
• No movement of runtime read routing, sessions, or proofs out of lib.rs
• 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 semantic risk. The sixteen wrappers and spans moved intact and still call the same domain SQL functions with the same pool, arguments, return types, and ordering. Existing user/DM records, parsers, helpers, SQL, and tests remain in their owning modules.

Blox Verification

Author workstation: buzz-tornquist-issue-2-store-stack (2046520), exact head 9e63d4ad728ed893a32e923d56d66e58d9ca7599.

• cargo fmt --all --check and git diff --check — passed
• cargo clippy -p buzz-db --all-targets -- -D warnings — passed
• cargo clippy -p buzz-relay --all-targets -- -D warnings — passed
• cargo test -p buzz-db --quiet — 108 passed, 200 ignored
• Native PostgreSQL user::tests:: ignored suite — 8 passed
• DM focused unit tests — 4 passed as part of the DB suite
• cargo test -p buzz-relay --lib -- --test-threads=1 — 909 passed, 48 ignored
• Commit-time formatting, sadscan, attribution, and sign-off hooks — passed
• Review follow-up moved the misplaced Tests section header below the production DM wrapper block; exact-head fmt, diff, and ownership checks passed

Independent exact-head Blox review: buzz-tornquist-pr-6796-review (2051741) verified final head 9e63d4ad728ed893a32e923d56d66e58d9ca7599, 16/16 wrapper equivalence, 16/16 byte-identical SQL functions, unique spans, unchanged tests apart from the scoped scanner suppression, and the retained runtime routing boundary. The reviewer found the misplaced Tests header, confirmed the comment-only fix on the final head, and reported no remaining findings. Formatting, diff, DB/relay clippy, 108 DB tests, 8 user PostgreSQL tests, 4 DM tests, ownership checks, the sadscan staged probe, and final 909 relay tests passed. The review workstation was deleted after artifact verification.

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.

Outcome

No actionable findings.

Reviewed exact base ecd17550f7e6e7b4f25399a546072177a0eb20a6 through exact head 48822f008819089618593edcee78bb468a21ec05 on fresh Blox workstation buzz-tornquist-pr-6796-final-review (ID 2057634). The range contains the ownership extraction commit plus its documentation-only follow-up. Nine user wrappers and seven DM wrappers retain their signatures, calls, SQL owners, types, and single datastore spans; route/session infrastructure remains in lib.rs.

Verification

• Formatting, range/worktree diff checks, touched-crate clippy, and clean-tree checks passed.
• Non-PostgreSQL tests: user 5 passed/8 ignored; DM 4 passed.
• Relay consumer compile passed.
• Native PostgreSQL 17: all 8 ignored user tests passed; the DM module has no ignored PostgreSQL tests.
• Exact head and base merge-base were rechecked.

No code edits or external mutations were made. Buzz relay credentials/ownership reporting were unavailable under the documented fallback. The workstation was deleted after artifact transfer.

Artifacts

• Diff SHA-256: 9a62ded16afce24a3ffb04f83c8c6f9838f413675f3877cc1cbae92bcec21915
• Verification log SHA-256: e848ac25a588eaec7d2e983e659640dedf6efc8ed642bb8f79d694ea72cb19d2
• Artifact archive SHA-256: a1047df1b60e4f3dedc43b116cce62dc6147c36603b73984b325200c0d2b3229

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: 30621460f04c38467ea0df1731fce2763d696c04
• Exact head: d6abdf916ea53ad59e9f1d909db5256a06c2a661
• 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 buzz-db Clippy, current ownership/observability guards, user/DM unit tests, all 8 user PostgreSQL tests, and relay compilation.

[TheSentinel454]

🤖 Superseded by #6987, which consolidates the remaining issue #2 store-extraction stack onto merged #6782. #6987 is an open draft at the independently reviewed exact head, and all exact-head CI checks are green. This PR remains available for review history; please continue review on #6987.