[mhutchinson]

Summary

Part 2a in the vindex v1 upstreaming stack (extracted from #172 so the spec, ecosystem vision, and high-level architecture can be reviewed before the individual subcomponent design docs in #172 / Part 2b).

• Updates vindex/docs/tlog-vindex.md:
  • Simplifies c2sp.org/tlog-vindex-state@v1 to a strict 6-line unsigned input state commitment (input-origin, from, input-size, input-root, mpt-root), decoupling /keys verification from Input Log signature schemes and witness policies while advising operators to retain signed Input Log checkpoints out-of-band.
  • Shelves the pre-1.0 in-band map-fn commitment (recorded in ## Design Log pending ecosystem discussion on encoding and verification).
  • Parameterizes the Output Log symmetrically with <output-log-origin> and a checkpoint verification policy (dropping tlog-policy from the spec).
  • Drops the advisory limit query parameter on GET <index-url>/values for deterministic HTTP caching, drops the cross-lookup stateful commitment cache requirement, clarifies empty-range (from = input_size) empty_mpt_hash verification, and adds an explicit caller coverage-horizon check for from.
• Adds vindex/docs/APPLICATIONS.md: Illustrates how Certificate Transparency, Merkle Tree Certificates, Go SumDB, Sigstore, and Sigsum map onto VIndex—who monitors each log, canonical key shapes, query-time prefix proofs, and epoch rotation (from > 0).
• Adds vindex/docs/ARCHITECTURE.md: Defines the high-level 5-stage Map Sandwich pipeline, checkpoint promotion invariants, crash consistency model, auditing boundaries, operational characteristics, and architectural trade-offs.
• Updates vindex/README.md: Aligns high-level terminology and indexes the core specification, applications, and architecture documents.

PR Stack Roadmap

1. docs(vindex): retire legacy MVP and add C2SP tlog-vindex specification (docs(vindex): retire legacy MVP and add C2SP tlog-vindex specification #171)
2. 2a: docs(vindex): update tlog-vindex spec and add applications and architecture docs (this PR)
   2b: docs(vindex): add subcomponent design documentation (docs(vindex): add subcomponent design documentation #172, stacked on 2a)
3. feat(vindex): add wire codecs and metrics leaf packages
4. feat(vindex/mapfn): add WASM guest SDK, wazero sandbox host, examples, and CLI
5. feat(vindex/ingest): add tile-cached ingestion pipeline
6. feat(vindex/kvstore): add Pebble inverted chunk storage engine
7. feat(vindex/tree): add variable-length MPT state trie and output log publisher
8. feat(vindex): add sync coordinator and C2SP HTTP read server
9. feat(vindex/client): add verifiable C2SP client SDK and top-level Engine API
10. feat(vindex/auditor): add independent full-log auditor
11. feat(vindex/hammer): add continuous load-testing and verification hammer
12. feat(vindex/cmd): add vindexd daemon, client CLI, dashboards, and e2e suite
13. feat(vindex/sumdb): add Go SumDB index/verify binaries, Docker stack, and quickstart
14. feat(vindex/mtc): add MTC and Static-CT personalities, clonelog, and auditor CLI