Removing mxpic_forge from dependency

README.md

@@ -4,8 +4,8 @@
 The EDA repo owns canvas editing, YAML export, login, and API routing. This
 repo owns the Nazca-based GDS build flow: it reads saved cell YAML files,
 loads the selected technology manifest, loads PDK GDS assets, registers
-routable pins, connects bundle links through `mxpic_forge.Route`, and exports
-the final GDS.
+routable pins, connects bundle links through `mxpic_forge.Route` when available
+or Nazca `interconnects.Interconnect` as a fallback, and exports the final GDS.
 
 ## High Level Flow
 
@@ -34,10 +34,12 @@ Canvas Build GDS
 -> downloadable <project>.gds
 ```
 
-If `mxpic_router`, `mxpic_forge`, Nazca, or optional `gdstk` are absent, the
+If `mxpic_router`, Nazca, or optional `gdstk` are absent, the
 EDA server can still run canvas and login pages. Build actions are where the
-router stack is required. For Build Layout, the YAML is still saved and SVG
-preview is skipped when the router stack is missing.
+router stack is required. `mxpic_forge` improves routing when present, but is
+not required because the router falls back to Nazca Interconnect. For Build
+Layout, the YAML is still saved and SVG preview is skipped when the required
+router stack is missing.
 
 ## Runtime Stack
 
@@ -51,18 +53,21 @@ require_router_stack()
 -> import mxpic_router
 -> import nazca
 -> optionally import gdstk for SVG preview
--> import mxpic_router.builder._import_mxpic_forge_route()
-   -> adds sibling ../mxpic_forge to sys.path
-   -> removes any already-loaded non-forge mxpic modules
-   -> from mxpic import Route
+-> import mxpic_router.builder._import_route_backend()
+   -> first tries mxpic_router.builder._import_mxpic_forge_route()
+      -> adds sibling ../mxpic_forge to sys.path
+      -> removes any already-loaded non-forge mxpic modules
+      -> from mxpic import Route
+   -> if mxpic_forge is absent:
+      -> uses nazca.interconnects.Interconnect through a Route-compatible adapter
 ```
 
 Important package naming:
 
 - `mxpic_router` is this active router package.
 - `mxpic_router_legacy` is the old internal legacy package.
-- `mxpic` should resolve to `mxpic_forge`, because `mxpic_forge` provides
-  `Route`.
+- `mxpic` should resolve to `mxpic_forge` when that checkout is present,
+  because `mxpic_forge` provides the preferred `Route` backend.
 
 ## Inputs To mxpic_router
 
@@ -415,7 +420,7 @@ bundles:
 For each link:
 
 ```text
-builder._route_link(link, pin_map, Route, warnings)
+builder._route_link(link, pin_map, RouteBackend, warnings)
 -> route = Route(
        radius=link.radius or 10,
        width=link.width,
@@ -455,7 +460,7 @@ otherwise            -> bend_p2p
 missing method       -> fallback to sbend_p2p
 ```
 
-Then it calls the selected `mxpic_forge.Route` method:
+Then it calls the selected route backend method:
 
 ```python
 route_method(
@@ -492,7 +497,7 @@ mxpic_router/eda_loader.py
 
 mxpic_router/builder.py
 -> import Nazca
--> import mxpic_forge Route
+-> import mxpic_forge Route or Nazca Interconnect fallback
 -> apply technology manifest
 -> load all project YAML specs
 -> build basic, project, and PDK instances
@@ -510,9 +515,11 @@ mxpic_router_legacy/
   definitions. The frontend route editor and Nazca build path both consume it.
 - Keep PDK component metadata YAML beside its GDS files. The router needs that
   metadata to recreate pins after `nd.load_gds`.
-- Avoid reintroducing an internal `mxpic` package inside this repo. The name
-  `mxpic` must continue to resolve to `mxpic_forge`.
+- Avoid reintroducing an internal `mxpic` package inside this repo. When the
+  forge checkout is present, the name `mxpic` must continue to resolve to
+  `mxpic_forge`.
 - When adding a new routing family or xsection, update `technology.yml` first,
-  then verify that `mxpic_forge.Route` supports the required route method.
+  then verify that the selected route backend supports the required route
+  method.
 - When adding a new component source, make sure it eventually contributes pins
   to `pin_map`; otherwise bundle links can load but cannot route.