docs(selftest): add binding render-path selftest standard

HellionChat/SelfTests/README.md

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+# HellionChat SelfTest Standard
+
+These steps run in-game via `/xlperf`. They are HellionChat's real test layer:
+Dalamud-coupled classes cannot be instantiated in an xUnit AppDomain, so the
+honest verification path is the running plugin, not a headless harness.
+
+## The render-path rule (binding for every step)
+
+A SelfTest exists to catch a broken **runtime** path. To do that it MUST:
+
+1. **ENTRY = the real runtime entry the game calls** per frame or on the real
+   action — `HonorificHeader.Draw`, `ChunkRenderer.DrawChunks`,
+   `InputBar.TrySend`, `Sidebar.Draw`, `MessageList.Draw`,
+   `Lender<PayloadHandler>.Borrow()`. NEVER a helper only the test calls.
+2. **ASSERT observable state produced _through_ that entry** — a rendered or
+   suppressed slot, a set flag, a held vs. sent message. Do NOT re-implement the
+   helper's logic inside the test and assert against your own copy.
+3. **Wire first.** Where the real path does not yet call the correct helper,
+   wiring it is part of the restoration work; the SelfTest verifies only after.
+
+## Reviewer trick (run before trusting any step)
+
+For every helper a step calls:
+
+```bash
+grep -rn '<Helper>' HellionChat/ | grep -v SelfTests | grep -v Tests
+```
+
+Zero non-test callers = false-green suspect. The step is passing on dead code.
+
+## The hard gate
+
+Green steps + clean build + clean csharpier are NOT sufficient. In-game smoke
+(Linux/Wine, via `/xlperf`) is the true gate. Where headless cannot honestly
+verify (scroll state, real send, atlas rebuild, warm object pools), mark the
+step explicitly as smoke-only instead of faking a headless pass.
+
+## Anti-pattern of record
+
+`HonorificService.ShouldRenderSlot` had zero production callers and was green
+only because the test called it directly — a test passing on a path the game
+never runs. That is the failure this standard prevents.
+
+## Step classification
+
+The current real-path / helper-only / mixed classification of every registered
+step (with false-green suspects flagged) lives in the Obsidian vault:
+`Projekte/FFXIV/Hellion Chat/Audits/HellionChat SelfTest-Klassifikation 2026-05-29.md`.