Unblock Fruix checkout runtime on FreeBSD

docs/PROGRESS.md

@@ -1564,3 +1564,54 @@ Current assessment:
   - first make the upstream-derived checkout runnable on FreeBSD,
   - then introduce a deliberate `fruix` command boundary,
   - rather than destabilizing the codebase with a whole-tree `guix`/`gnu` rename too early
+
+## 2026-04-01 — Phase 5.1 completed: checkout runtime unblocked and first `fruix` frontend boundary established
+
+Completed work:
+
+- added a reusable phase-5 checkout setup helper:
+  - `tests/guix/setup-phase5-checkout.sh`
+- added a checkout runtime patch queue for the upstream-derived source tree:
+  - `tests/guix/patches/phase5-checkout-runtime.patch`
+- added a FreeBSD daemon/build patch queue needed for later phase-5 work:
+  - `tests/guix/patches/phase5-guix-daemon-freebsd.patch`
+- added a runtime validation harness:
+  - `tests/guix/run-phase5-checkout-runtime.sh`
+- wrote the Phase 5.1 report:
+  - `docs/reports/phase5-checkout-runtime-freebsd.md`
+- ran the runtime harness successfully and captured metadata under:
+  - `/tmp/phase5-runtime-metadata.txt`
+
+Important findings:
+
+- the earlier checkout blocker
+  - `./pre-inst-env guix --version`
+  - `Wrong type to apply: #<syntax-transformer leave-on-EPIPE>`
+  is now explained by top-level definition ordering in `guix/ui.scm`:
+  - `show-version-and-exit` called `leave-on-EPIPE` before the syntax transformer was defined later in the file
+  - on this FreeBSD path, that became a runtime application of a syntax-transformer object instead of a macro expansion site
+- the phase-5 runtime patch fixes this by:
+  - making `(guix ui)` explicitly non-declarative
+  - rewriting `show-version-and-exit` to use direct `catch 'system-error` handling
+  - parameterizing `program-name` in `guix-main`
+  - deriving the top-level version banner name from `program-name`
+  - making `(guix scripts repl)` explicitly non-declarative as well
+- the checkout now successfully runs the following commands on FreeBSD:
+  - `./pre-inst-env guix --version`
+  - `./pre-inst-env guix repl --help`
+  - `./pre-inst-env guix build --help`
+- the first user-facing Fruix command boundary is now implemented in the checkout setup via:
+  - `scripts/fruix`
+  as a front-end alias next to `scripts/guix`
+- observed runtime metadata confirmed:
+  - `first_guix_version_line=guix (GNU Guix) ...`
+  - `first_fruix_version_line=fruix (GNU Guix) ...`
+- this matches the agreed naming policy:
+  - Fruix at the user-facing boundary
+  - stable upstream-derived internal `guix`/`gnu` names unless there is a concrete reason to rename them
+
+Current assessment:
+
+- Phase 5.1 is now satisfied on the current FreeBSD prototype track
+- the key boundary has shifted from “the checkout still crashes immediately” to “the checkout runs, and can now be used as the basis for real derivation/store experiments”
+- the next step is to prove that a real derivation can be emitted against `/frx/store` from the now-runnable checkout