Document FreeBSD base self-hosting decision

docs/PROGRESS.md

@@ -3624,3 +3624,58 @@ Current assessment:
   - side-by-side native base outputs in `/frx/store`
   - rollback to the earlier closure without mutating it in place
 - the remaining Phase 15 work is to document the evidence-based decision on whether self-hosted base builds should be the next step, or whether host-built native base artifacts should remain the near-term path while reproducibility/source acquisition improve
+
+## 2026-04-03 — Phase 15.3: decided not to pursue self-hosted base builds yet
+
+Completed work:
+
+- wrote the Phase 15.3 report:
+  - `docs/reports/phase15-self-hosting-decision-freebsd.md`
+- updated the high-level summary:
+  - `docs/PROG_SUMMARY.md`
+- recorded an evidence-based decision about the next architecture step after Phases 13–15
+
+Decision:
+
+- do **not** pursue self-hosted FreeBSD base builds as the next immediate milestone
+- keep the near-term path on:
+  1. host-built native FreeBSD base artifacts from `/usr/src`
+  2. storage in `/frx/store`
+  3. stronger declarative source-tree/version selection and provenance
+  4. tighter reproducibility around source inputs and build parameters
+- only revisit guest self-hosting after those pieces are stronger
+
+Evidence used for the decision:
+
+- Fruix already builds native FreeBSD base artifacts from `/usr/src` into `/frx/store`
+- Fruix already validates a host-base-free boot/runtime path composed from:
+  - `freebsd-native-kernel`
+  - `freebsd-native-bootloader`
+  - `freebsd-native-runtime`
+- that path already boots on:
+  - local QEMU/UEFI/TCG
+  - the approved real XCP-ng VM/VDI path
+- the FreeBSD base is now an explicit declarative input through `freebsd-base`
+- Fruix now supports side-by-side declared base versions and rollback-friendly redeploy
+- the most important remaining reproducibility gap is now source-tree selection/acquisition, not host-copy boot/runtime assembly
+- environment constraints still argue for caution before a self-hosting pivot:
+  - local bhyve remains blocked under Xen due to missing nested VT-x exposure
+  - real validation still reuses a single approved XCP-ng VM/VDI pair
+  - XCP-ng storage permissions still prevent creating fresh VDIs on demand
+
+Current assessment:
+
+- Phase 15.3 is complete
+- Phase 15 is fully complete
+- Fruix now has:
+  - a host-base-free native FreeBSD boot/runtime path in `/frx/store`
+  - an explicit declarative FreeBSD base model
+  - side-by-side base-version coexistence in `/frx/store`
+  - rollback-friendly redeploy across declared base versions
+  - a documented decision to continue with host-built native base artifacts for now rather than jumping immediately to guest self-hosting
+
+Next recommended step:
+
+1. focus the next phase on making FreeBSD source-tree selection/acquisition more declarative and reproducible
+2. keep improving provenance and source-input identity around the now-working native base path
+3. revisit self-hosted base builds only after the source/reproducibility boundary is substantially stronger