glm-5.3-flash
8f73da5d12
Architecture documentation structure per sdd_process phase 1: - README index (doc table, ADR table, lifecycle), overview with crate map, dependency rules, and security invariants - Component specs: storage, transport, http, ssh, alkgitd (all draft) - ADRs 001-009: crate decomposition, front-door-blind core, V2-first protocol, pack pipeline (data::output generation / data::input ingestion), session substrate types, http adapter composition (proposed, OQ-01), ACL-before-advertisement, registry-resolved repo identity, bounded-resources budgets - open-questions.md: OQ-01..08 with two deferred(scope), one deferred(unclear), door-type definitions, blocker tracker tasks in tasks/architecture/ - v1 ssh-door decision recorded: russh terminates wire SSH in alkgitd; alkcall channels stay the internal substrate (OQ-03 partially resolved) Two review rounds (fresh-context subagent): 4 critical + 17 warnings fixed in round one; zero critical + 4 warnings + 5 suggestions fixed in round two. All ADR/OQ cross-references verified resolving.
82 lines
3.8 KiB
Markdown
82 lines
3.8 KiB
Markdown
# ADR-003: Protocol V2-first with honest capability advertisement
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## Status
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Accepted
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## Context
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The git smart protocol has three versions in the wild: V0 (the original),
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V1 (capability line prefixed), and V2 (command-based, default since git
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2.18+). POC-1 and POC-2 validated the full V2 fetch path against real git
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2.43 end-to-end (advertisement, ls-refs, fetch with sideband packs) over
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both duplex and http substrates. V0/V1 stateless-http is a different
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framing (per-round POSTs, stateless ack re-derivation).
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The research inventory (`git-protocol.md` §"Open items") left the V0/V1
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question open: support V0/V1 on http? On ssh? Which first?
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Decision drivers:
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- Our deployment anchor (vision §"Primary deployment target") is modern
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git clients over http and ssh; every git client from the last six years
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speaks V2.
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- Honest capability advertisement (vision principle 5) is easiest to keep
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honest with fewer served shapes.
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- V0/V1 stateless-http needs multi-round negotiation state re-derivation —
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meaningful complexity for a client population that is effectively
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extinct.
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## Decision
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**Serve protocol V2 first.** alkgit v1 serves V2 on both doors:
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- Advertisement is once-per-session (duplex) / per-request-set (http),
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exactly as observed in POC-1 (re-advertising between commands hangs real
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git).
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- Advertised capabilities are exactly what we serve: `ls-refs=unborn`,
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`fetch=wait-for-done` (v1 fetch policy is full-closure pack on `done`;
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multi-round negotiation, OQ-02, may add capability values when it
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lands), `object-format=sha1` (+ sha256 under the feature flag, if and
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when tested — OQ-05). Nothing unimplemented is advertised
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(shallow, filter, packfile-uris, object-info, server-option are
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*declined by omission*; POC-1 confirmed real git accepts this).
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On the push side, `git-upload-archive` is not served at all — ssh
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exec requests for it get a fixed refusal (ssh.md; ADR-008's
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never-execute rule).
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- HTTP requests protocol V2 only; ssh requests protocol V2 only (see
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below).
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**V0/V1 policy: decided now as V2-only for v1.** Both doors
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(http and ssh) speak V2; clients that cannot speak V2 get a clear pkt-line
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error. Reversal is wire-visible (the advertised version set is a wire
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format), so treat this as effectively one-way once published — the
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decision is still made now, and revisiting it needs a new ADR plus a
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deprecation window for clients. The motivation stands: a concrete consumer
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needing V0/V1 (e.g. very old CI images) has not been identified.
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The V0/V1 receive-pack shape (used by `git push` on http stateless framing
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in older clients) is unaffected by this choice: receive-pack is mostly
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version-independent (see transport.md).
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Sequencing note (fixes the scope contradiction the review found): the v1
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fetch policy that ships first is full-closure-on-`done` (POC-validated).
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Multi-round V2 negotiation (haves/acks without `done`) is in v1's *scope*
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but lands after the done-path works end-to-end; its ack logic is OQ-02's
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open question, and any capability-advertisement change it requires
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happens then.
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## Consequences
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- Smallest honest surface; POC-validated shapes only.
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- Old-client support is declined explicitly (error, not silence).
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- The POC's observed `done`-path shape (no acknowledgments section, no
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`ready`, response ends at flush) is our normative wire behavior, not the
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docs' grammar — `git-protocol.md` §V2 records this.
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- If V0/V1 is ever added, the state machines in transport must be
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re-shaped around a version-dispatch at session start (single point, by
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design — see ADR-005).
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## References
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- `docs/research/git-protocol.md` §"Protocol surface inventory", §"Negotiation policy"
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- `docs/research/poc-1-findings.md` (advertisement-once, capability declination), POC-3 (http V2 framing)
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- ADR-005 (substrate types), ADR-007 (ACL before advertisement)
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- transport.md, http.md, ssh.md |