test: add render-contract assertion

Adds a 9th assertion that drives widget.render(ctx) with a stub ctx
shaped per lib-core.panel's widget-lifecycle contract (bounds, theme
with packed-RGBA colours and font_size_body, is_focused) and verifies
the widget populates _render_rows correctly. Catches future drift
between this widget and the panel API.

engine.render.draw_text is registered but errors in test_mode (no
OpenGL context); the assertion stubs it for the duration of the
render call so the layout pass runs to completion without coupling
to the rendering backend.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

init.lua

@@ -1,6 +1,7 @@
 -- lib-core.crafting-display-test — v0.1.0
--- 8 assertions covering widget creation, action lifecycle, default-empty,
--- row visibility (is_known filter), per-row availability, and resolver overrides.
+-- 9 assertions covering widget creation, action lifecycle, default-empty,
+-- row visibility (is_known filter), per-row availability, resolver overrides,
+-- and the panel widget-contract (render(ctx) populating _render_rows).
 -- Pattern follows P.2.4 Test-Module-Pattern; TAP output via engine.test.*
 
 local composition = require("lib-core.composition")
@@ -221,6 +222,45 @@ function M.run_tests(_ctx)
     local summary8 = display._test_resolve_summary(widget8, recipe8)
     T.assert(icon8 == "ICON_X" and label8 == "LABEL_X" and summary8 == "SUMMARY_X",
         "8. resolver overrides (icon/label/summary) invoked after set_*_resolver")
+
+    -- ================================================================
+    -- §9: widget.render(ctx) with a panel-shaped ctx populates
+    --     widget._render_rows. Drives the panel widget contract:
+    --     render(ctx) where ctx = {bounds, theme, is_focused}. Catches
+    --     contract-drift between this lib and lib-core.panel.
+    -- ================================================================
+    local container9 = setup_container{}
+    crafting.define_recipe{
+        id     = "render_r9",
+        inputs = { { template = "craft_display_test.rock", count = 1 } },
+        output = { template = "craft_display_test.rock_pick", count = 1 },
+        name   = "Render Recipe",
+    }
+    local widget9 = display.create(container9, { title = "C", widget_id = "cw" })
+    local ctx9 = {
+        bounds     = { x = 0, y = 0, w = 400, h = 300 },
+        theme      = {
+            row_height     = 28,
+            padding        = 8,
+            text_color     = 0xFFFFFFFF,
+            text_color_dim = 0x999999FF,
+            font_size_body = 14,
+        },
+        is_focused = false,
+    }
+    -- engine.render.draw_text is registered but errors in test_mode (no
+    -- OpenGL context); stub it for the duration of this render call so
+    -- the layout pass runs to completion.
+    local saved_draw_text = engine.render.draw_text
+    engine.render.draw_text = function() end
+    local render_ok, render_err = pcall(widget9.render, ctx9)
+    engine.render.draw_text = saved_draw_text
+    T.assert(render_ok
+                 and widget9._render_rows ~= nil
+                 and #widget9._render_rows == 1
+                 and widget9._render_rows[1].recipe_id == "render_r9",
+        "9. widget.render(ctx) per panel widget contract populates _render_rows"
+            .. (render_ok and "" or (" (render errored: " .. tostring(render_err) .. ")")))
 end
 
 return M