docs(adr-0056): Scoop+Homebrew validated; record the Caddy HEAD fix

Amendment 3: scoop install and brew install both verified end-to-end on
real Windows + macOS (install + run), resolving Amendment 2's unverified
caveats (incl. the HEAD:main push).

Records the root cause + fix for the Homebrew 403: Gitea (>=1.25)
303-redirects release downloads to a method-bound SigV4 presigned S3 URL;
brew resolves with HEAD, captures the HEAD-signed URL, then GETs it -> 403
(GET-only tools are unaffected). Fixed by a server-side Caddy rule that
answers HEAD on release-download paths directly (200, no redirect) so the
download GET re-runs the redirect fresh. That rule lives in the Gitea edge
config, NOT this repo - documented so a server rebuild doesn't silently
break brew. Includes the reference Caddyfile block.

Also notes the ad-hoc mac signature runs fine via brew; Developer-ID +
notarization stays parked on the Apple org conversion. Remaining D3: winget.

docs/adr/0056-crates-io-and-cargo-binstall.md

@@ -176,3 +176,65 @@ whether macOS Gatekeeper accepts the **ad-hoc-signed** mac binary via
 requirement and `brew`'s curl download sets no quarantine xattr, unlike a
 browser download — but this rides on the still-parked Developer-ID signing
 decision). **Remaining D3:** winget (komac on Linux CI, or a manual PR).
+
+## Amendment 3 — 2026-06-19: validated end-to-end; a presigned-URL/HEAD gotcha + the Caddy fix it needs
+
+**Scoop and Homebrew now install and run end-to-end** (`v0.2.0`,
+user-verified on real Windows + macOS): `scoop install rdbms-playground`
+and `brew install lazyeval/tap/rdbms-playground` both fetch, checksum,
+install, and the installed binary launches. Amendment 2's "unverified"
+caveats are resolved (the `HEAD:main` push populated both repos cleanly).
+
+**Distribution depends on a server-side Caddy rule — RECORD THIS: it lives
+in the Gitea edge config, NOT this repo, and if it is lost in a server
+rebuild Homebrew silently 403s again.** Symptom: `brew install` failed with
+`curl (22) … 403` on the asset URL. Root cause: Gitea (≥1.25; here 1.26.2)
+serves release-asset downloads by **303-redirecting to a method-bound
+AWS-SigV4 presigned S3 URL** (OVH), signed for the *incoming* request's HTTP
+verb. Homebrew **resolves the URL with a HEAD, captures the returned
+(HEAD-signed) presigned URL, then runs the download GET against that
+captured URL** → GET-on-a-HEAD-signed-URL → 403. Reproduced precisely:
+`GET on HEAD-resolved = 403`, `HEAD on HEAD-resolved = 200`, `GET on
+GET-resolved = 200`, `HEAD on GET-resolved = 403`. GET-only tools
+(`install.sh`, `install.ps1`, `cargo binstall`, curl) are unaffected — they
+GET the original URL and let it redirect fresh to a GET-signed URL. This is
+a **Homebrew defect** (it reuses an ephemeral, method-scoped credential as
+if it were a durable resource locator); Gitea's per-request method-bound
+signing is correct, and SigV4 *cannot* sign one URL for two verbs.
+`SERVE_DIRECT=false` (Gitea proxies, no presign) would also fix it but was
+declined — not reshaping storage for one client.
+
+**Fix (deployed, "Tier A"): a Caddy rule that answers HEAD on
+release-download paths directly** — 200, no redirect, no body — so brew's
+resolve records the *original* URL (no presigned credential captured) and
+its download GET runs through the redirect fresh → GET-signed → 200. Scoped
+to `method HEAD` + the release-download path; **GET is untouched**, so every
+working channel is unaffected, and a HEAD carries no payload so no client
+can *break* (at most a HEAD-probing download manager loses a progress-bar
+size — cosmetic). Reference Caddyfile (place before the Gitea
+reverse_proxy):
+
+```
+@release_head {
+    method HEAD
+    path_regexp ^/[^/]+/[^/]+/releases/download/.+
+}
+handle @release_head {
+    header Accept-Ranges bytes
+    header Content-Type application/octet-stream
+    respond 200
+}
+```
+
+A "Tier B" variant (a sidecar that fetches and returns the *real*
+Content-Length so even HEAD-probing clients stay fully faithful) was specced
+but proved unnecessary — brew is happy with the bare 200.
+
+**macOS signing:** the brew-installed binary **runs** under the current
+**ad-hoc** signature (`codesign --sign -`) — confirmed on Apple Silicon.
+**Developer-ID signing + notarization remains parked** pending the user's
+Apple account conversion to an Organization (GA plan / ADR-ci-003); it is
+needed for *browser-download* trust, not for the package-manager paths,
+which are all working now.
+
+**Remaining D3:** winget only.