NIP-33: d-tag keyed replacement for parameterized replaceable events

[tlongwell-block]

What

Correct NIP-33 support for parameterized replaceable events (kind 30000–39999). The latest event per (author, kind, d_tag) wins — the foundation for editable, author-owned content on Nostr.

This is storage plumbing that unblocks PR 3 (kind:30023 long-form articles). No new kinds are accepted by the allowlist yet.

Why

Sprout already stores events in the 30000–39999 range (NIP-29 group metadata), but replacement keys on (kind, pubkey, channel_id) instead of the NIP-33-correct (kind, pubkey, d_tag). This works for relay-signed group metadata only because each group has a unique channel_id — but it is not correct NIP-33 behavior and would break for any user-submitted parameterized replaceable events.

How

Schema — d_tag TEXT column on the events table + idx_events_parameterized partial index on (kind, pubkey, d_tag, deleted_at) WHERE d_tag IS NOT NULL.

Storage — extract_d_tag() at the shared insert layer populates d_tag for all events: NIP-33 kinds get the d tag value (or "" per spec), everything else gets NULL. New replace_parameterized_event() uses pg_advisory_xact_lock + stale-write protection + transactional insert to prevent both concurrent-insert races and the delete-without-reinsert bug.

Ingest — New routing arm between the existing replaceable and default paths for is_parameterized_replaceable() kinds. Oversized d tags (>1024 bytes) are rejected at ingest to preserve NIP-33 identity key fidelity — no silent truncation.

Query — #d tag filter pushed into SQL for NIP-33-only kind filters, preventing under-fetch on authors + kinds + #d lookups under LIMIT pressure. Gated to NIP-33 kinds so non-NIP-33 events (d_tag=NULL) are not silently excluded.

Backfill — Idempotent startup backfill in relay main + scripts/backfill-d-tag.sql + integrated into dev-setup.sh.

NIP-11 — NIP-33 added to supported_nips (alongside NIP-16 from PR 1).

What does NOT change

• NIP-29 group metadata (kind 39000–39002) continues using replace_addressable_event() via side_effects.rs — those events bypass ingest entirely
• Kind allowlist — no new user-submitted kinds are accepted (that is PR 3)
• Desktop UI, MCP tools

Testing

• 682 unit tests pass (cargo test --workspace --lib)
• Clippy clean (-D warnings), fmt clean
• All 7 pre-push hooks pass (rust-fmt, desktop-tauri-fmt, desktop-check, desktop-tauri-check, desktop-build, rust-clippy, rust-tests)
• Live tested against freshly built relay: channel creation, messaging, threading, reactions, profile replacement (kind:0), contact list replacement (kind:3), ACP agent discovery + reply — no regressions, zero errors in relay log
• Schema verified: d_tag column present on all partitions, partial index used by EXPLAIN, correct NULL/value population across all event kinds

Crossfire review

Three-model crossfire review (Codex GPT-5.4, 2× Claude 4.6 Opus). Final score: 10/10 APPROVE from Codex after two rounds of fixes:

1. NIP-33 in NIP-11 — supported_nips was inconsistently adding NIP-16 but not NIP-33. Fixed.
2. d_tag length bound — unbounded TEXT column accepted arbitrarily large values. Initially fixed with truncation, but Codex correctly identified that silent truncation mutates the NIP-33 identity key (two events sharing the first 1024 bytes would incorrectly replace each other). Changed to rejection at ingest.
3. Multi-value #d pushdown test — added coverage for the case where multiple #d values correctly fall back to post-filtering.

Files changed

File	What
schema/schema.sql	d_tag TEXT column + partial index
crates/sprout-core/src/kind.rs	is_parameterized_replaceable() + constants + tests
crates/sprout-db/src/event.rs	extract_d_tag(), D_TAG_MAX_LEN, d_tag in INSERT paths, EventQuery.d_tag, query builder, 10 unit tests
crates/sprout-db/src/lib.rs	replace_parameterized_event(), backfill_d_tags(), d_tag in replace_addressable_event()
crates/sprout-relay/src/handlers/ingest.rs	Parameterized replaceable routing + d_tag length rejection
crates/sprout-relay/src/handlers/req.rs	#d SQL pushdown (NIP-33 gated) + tests
crates/sprout-relay/src/main.rs	Startup backfill
crates/sprout-relay/src/nip11.rs	NIP-33 in supported_nips
scripts/backfill-d-tag.sql	Idempotent backfill script
scripts/dev-setup.sh	Backfill integration

Rollout

1. pgschema apply adds the column and index (declarative, automatic)
2. Relay startup runs backfill_d_tags() (idempotent, populates existing NIP-33 rows)
3. New events get d_tag populated automatically via extract_d_tag() at the insert layer