Add URP probe playbook (#7099)

docs/URP_MIGRATION_PLAN.md

@@ -146,6 +146,9 @@ Prioritize:
 After the baseline and inventory exist, create a throwaway probe branch. This is not
 the migration branch.
 
+Use `docs/URP_PROBE_PLAYBOOK.md` for the branch structure, probe steps, expected
+risk areas, and findings template.
+
 Probe goals:
 
 - install URP

docs/URP_PROBE_PLAYBOOK.md

@@ -0,0 +1,132 @@
+# URP Probe Playbook
+
+Last refreshed: 2026-06-11
+
+This playbook is for the disposable URP probe described in
+`docs/URP_MIGRATION_PLAN.md`. The probe is not the migration branch and should not
+be merged as-is. Its job is to answer what breaks when Unity's URP tooling is
+allowed to touch the project.
+
+## Goals
+
+- Install URP in an isolated branch.
+- Create the minimum URP pipeline/renderer assets needed to enter Play Mode.
+- Run Unity's Render Pipeline Converter.
+- Record compile errors, pink materials, broken shaders, and visual regressions.
+- Preserve findings in docs, then discard or reset the probe branch.
+
+## Branch Shape
+
+Use two branches:
+
+| Branch | Purpose | Mergeable |
+|---|---|---|
+| `codex/urp-probe` | Disposable package/settings/material conversion experiment | No |
+| `codex/urp-probe-findings` | Small docs-only summary copied from the probe | Yes |
+
+Do not open a PR from `codex/urp-probe` unless it is clearly marked draft and
+experimental. Prefer opening the PR from `codex/urp-probe-findings`.
+
+## Before Starting
+
+1. Confirm `origin/main` is fresh.
+2. Confirm the worktree is clean.
+3. Capture or review the baseline checklist in
+   `docs/URP_VISUAL_BASELINE_CHECKLIST.md`.
+4. Generate a current inventory with
+   `Eagle0 > Rendering > Generate URP Migration Inventory`.
+5. Keep the inventory output under Unity `Temp/`; do not commit generated reports
+   unless they are intentionally summarized.
+
+## Probe Steps
+
+1. Create `codex/urp-probe` from `origin/main`.
+2. Add the Universal Render Pipeline package using Unity Package Manager.
+3. Create a minimal URP Pipeline Asset and Renderer Asset under a clearly named
+   probe folder, such as `Assets/Settings/URPProbe/`.
+4. Assign the URP pipeline asset in:
+   - `ProjectSettings/GraphicsSettings.asset`
+   - `ProjectSettings/QualitySettings.asset`
+5. Run Unity's Render Pipeline Converter for materials.
+6. Enter Play Mode from `Assets/Scenes/Main.unity`.
+7. Exercise the baseline views:
+   - Connection lobby
+   - Eagle map
+   - Eagle weather and beast effects
+   - Shardok terrain, grid, labels, bridges, fires, overlays
+   - Connection -> Eagle -> Shardok -> Eagle transitions
+8. Record the exact failure mode for every broken visual:
+   - compile error
+   - pink material
+   - invisible mesh or sprite
+   - wrong render order
+   - lighting/shadow difference
+   - input or scene-load regression
+
+## Expected High-Risk Areas
+
+- Eagle province map shaders:
+  - `ProvinceMapShader`
+  - `ProvinceWeatherMapShader`
+  - `ProvinceWeatherShader`
+  - `ProvinceParticleShader`
+- Shardok map and overlay shaders:
+  - `Hex Mesh Shader`
+  - `maskShader`
+  - `ClipRectParticleUnlit`
+- Third-party 3D materials:
+  - Polytope Studio character prefabs used by Eagle human-type beast effects
+  - RRFreelance Orc/Ogre materials used by `OgreEffect`
+- Render ordering in Shardok:
+  - unit text/icons versus fires
+  - unit text/icons versus bridges
+  - selection/command overlays versus labels
+
+## Findings Template
+
+Copy this template into the mergeable findings branch after the probe:
+
+```markdown
+# URP Probe Findings
+
+Date:
+Unity version:
+URP package version:
+Probe branch commit:
+
+## Summary
+
+- Entered Play Mode:
+- Connection usable:
+- Eagle usable:
+- Shardok usable:
+- Build attempted:
+
+## Converter Results
+
+- Materials converted:
+- Materials left pink:
+- Shader compile errors:
+
+## Visual Regressions
+
+| Area | Expected | Actual | Likely Cause | Next Action |
+|---|---|---|---|---|
+
+## Required Migration PRs
+
+1.
+2.
+3.
+
+## Notes
+
+-
+```
+
+## After The Probe
+
+1. Copy findings into a docs-only branch.
+2. Delete or abandon `codex/urp-probe`.
+3. Do not merge probe-generated package/settings/material churn into main until the
+   findings have been reviewed and broken visuals have owner PRs.