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+# Iteration 19 — Phase 8 (close)
+
+Closes 2026-05-14. iter19 = test mechanism 2 (REINIT clears controls). DISPROVED. PARTIAL close.
+
+## α-23 test result
+
+Disabled `media_request_reinit()` in `RequestSyncSurface`. HEVC hash unchanged (`06b2c5a0…`); kernel printk still shows `w=0 h=0`. Reverted.
+
+Mechanism 2 (REINIT-clearing) **DISPROVED**.
+
+## Remaining mechanism after iter19
+
+Only mechanism 4 (ctrl_hdl mismatch — libva submits to one v4l2_ctrl_handler, rkvdec reads from another) remains untested. This requires deeper kernel printk: dump `&ctx->ctrl_hdl` pointer + the per-request handler pointer.
+
+Mechanism 1 (request_fd mismatch) is empirically unlikely — strace confirmed libva uses consistent request_fd across S_EXT_CTRLS, QBUF, and IOC_QUEUE for the same frame.
+
+## State at iter19 close
+
+Backend SHA on fresnel: `c1d4bb53…` (iter15 stable). Fork tip `415688d` (revert of α-23). Diagnostic kernel printk in rkvdec_hevc_run remains (linux-fresnel-fourier 7.0-3); useful for iter20+.
+
+5-codec anchors: unchanged. Zero regression from iter15.
+
+## Iter17 finding still load-bearing
+
+Three iterations (17, 18, 19) of investigation have eliminated 4 of 5 hypothesis mechanisms. The smoking-gun finding from iter17 remains:
+
+**rkvdec sees zero V4L2 controls for libva HEVC despite identical wire-byte payloads to kdirect.**
+
+The remaining mechanism (ctrl_hdl handler routing) requires kernel-side printk to confirm. iter20 candidate work.
+
+## iter20 next
+
+Add kernel printk in `rkvdec_hevc_run_preamble` that dumps:
+- `&ctx->ctrl_hdl` pointer address.
+- For each `v4l2_ctrl_find()`: `ctrl` pointer + `ctrl->p_cur.p` pointer + first 8 bytes of `*ctrl->p_cur.p`.
+
+Compare libva-trigger vs kdirect-trigger:
+- If both have same `&ctx->ctrl_hdl` and same `ctrl` per ID, but libva's `p_cur.p` has zeros while kdirect's has correct values — the `v4l2_ctrl_request_setup` (or analog) call during IOC_QUEUE isn't applying request-staged controls to ctx for libva.
+- If `&ctx->ctrl_hdl` differs — libva and kdirect are working on different control handlers entirely.
+- If `ctrl` differs by ID — control registration changed between contexts.
+
+Each outcome localizes the bug to a specific kernel layer.