SWIP-066: Graffiti wall pattern

[zelig]

The anti-GSOC: permissionless public write-boards (walls) named by any topic, where every entry is signed by its writer's own key — no shared graffiti key, ever. Writers buy wall membership with mining effort instead: an ephemeral owner (the MOC pattern, #80), a bare-index feed over a BPS broker (#104, carriage per #106), or a mined span-index — the feed index written into the span field of an empty-payload wrapped chunk, making the entry self-describing (id = H(T ‖ SPAN), owner recovered from the signature, PO(addr, H(T)) ≥ 16).

Highlights:

• Motivation enumerates 8 arguments against the shared-key GSOC pattern: the Book's single-owner integrity premise, pull-sync divergence (cf. SWIP-TBA - Chunk checksum for divergent sync #101), the wrapped-address complication in incentives, stamp reuse across versions, closest-node-only retrieval and cache opacity, single-response exhaustion, no censorship resistance, and collisions even on the honest path.
• Content feeds live one hash deeper: topic H(T) — which equals the anchor — so mined spans can never clash with sequential content ids.
• Aggregation: a BPS broker on the wall's cohort doubles as the aggregate feed indexer by publishing its own self-indexed (SWIP-065: Self-indexed feeds #106) feed of contributors — after-the-fact reading is a single feed lookup; the broker can withhold but cannot forge.
• Worked example: tag-based advertising over tag-combination walls.
• DISC: NO — standard SOC validation, existing PO_MIN rule, arbitrary-span empty-payload wrapped chunks already allowed.

Freestanding pattern in the SWIP-59/60/61/65 family (#103, #104, #105, #106). Work-package format; open guesses are marked (?) in the text and being resolved in dictation rounds.

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[zelig]

Round 4 (449a964): restored the accidentally omitted H(A‖C) tag combination; the worked example now states that for this ad type no content feed is needed — the entry's existence gives the information — with a matching MAY-be-absent note in mode 3; mining helpers homed in client libraries (bee-js or other JS libs); withhold-never-forge wording confirmed. Remaining (?): broker contributors-feed parameters and dedup granularity.

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[zelig]

Broker contributors-feed parameters confirmed: owner = the broker's key, topic = H(T). Last open (?): feed granularity — one update per wall entry observed, or dedup to one per contributor.

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[zelig]

Granularity resolved: the contributors feed is self-indexing with one update per wall entry observed — the choice most compatible with the pot's default timestamp key — with per-contributor dedup mentioned as a broker MAY. No open question marks remain in the draft.

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