Design Gate — #3184 fleet-internal release bless = Gitea private cargo

Problem

Agents treat crates.io / GitHub Releases as canonical for terraphim_grep and terraphim_agent. Guardian blesses 1.21.1 on the Gitea private cargo registry while crates.io sits at 1.20.5 and the GitHub release tag at v1.20.5 — so agents report false release failures. Nothing in-repo encodes the channel precedence. Docs-only slice of ops issue #3183.

Decision (exact touchpoints)

1. NEW docs/src/release-channels.md — policy doc. Placed under the mdBook src root (verified docs/book.toml → src = "src") so it renders and sits beside existing docs/src/release-process.md. The issue's docs/release-channels.md would be outside the book; this satisfies the same AC.
2. EDIT docs/src/SUMMARY.md — add - [Release Channels](./release-channels.md) near the Contributing/Branch Protection block.
3. EDIT README.md ## Installation Methods (~line 591), under #### Direct Download — note that GitHub Releases are not the fleet-canonical channel; link to the new doc.

Ground truth (verified 2026-08-08, live)

• GET {GITEA_URL}/api/v1/packages/terraphim/cargo/{name} → HTTP 200, returns a JSON array, one object per version. Fields per object: id, owner.login, repository (null), creator, type: "cargo", name, version, html_url, created_at. There is no latest field — the doc must say "max version in the array", not "read .latest". List form: GET /api/v1/packages/terraphim?type=cargo.
• Blessed: terraphim_grep 1.21.1 (3 versions), terraphim_agent 1.21.1 (3 versions). Package names use underscores.
• Lag confirmed: crates.io 1.20.5 both crates; GitHub release v1.20.5; Gitea tag v1.21.0.
• Guardian verdict CONDITIONAL_PASS; lag = WARN checks R6/R6cargo/R6cargo-rel; R6canon PASS = fleet bless 1.21.1. Smokes R7:* PASS, path=terraphim-clients, temp-root.
• Guardian lives at /home/alex/projects/cto-executive-system/release-guardian/ (not private/… as the issue states) — external to this repo: reference by name, never a relative link.

Acceptance criteria

• AC1 Doc states: canonical = Gitea cargo registry, owner terraphim; blessed 1.21.1 for grep+agent; crates.io/GitHub lag is CONDITIONAL, not failure for fleet-internal; install smoke is temp-root only with path install from terraphim-clients when the private sparse index is unavailable.
• AC2 README Installation Methods links to it.
• AC3 Doc names release-guardian for continuous checks and cites evidence reports/2026-08-08-terraphim-ai-clients.md and adf-ledger.jsonl (as paths, not links).
• AC4 PR to main; structural-pr-review 5/5, zero P1/P2.

Non-goals

• Publishing to crates.io / GitHub Releases (ops #3183). No version bumps, no Cargo/CI changes.
• No automated registry checking in this repo (guardian owns it); no edits under cto-executive-system/; no re-running smokes.

Test plan

• Unit: none — zero code changes; asserted by git diff --stat touching only .md.
• Links resolve (ls each target); mdbook build docs emits release-channels.html.
• Live (re-run and paste in PR): curl -s -H "Authorization: token $GITEA_TOKEN" \ "$GITEA_URL/api/v1/packages/terraphim/cargo/terraphim_grep" | jq -r '.[].version' → includes 1.21.1.
• No wiremock: no in-repo code path consumes this API, so there is nothing to stub.

Gates

cargo fmt --all -- --check
cargo clippy --workspace --all-targets -- -D warnings   # no-op, docs-only
cargo test --workspace                                   # unchanged
mdbook build docs                                        # book.toml is at docs/book.toml

Pre-commit hooks must pass: conventional commit docs(release): … Refs #3184; secret scan — never paste a GITEA_TOKEN value into the doc, use $GITEA_TOKEN placeholders only.