# Goal-1 (clean, layered host architecture) — staged execution plan

The design is in [`windows-host-rewrite.md`](windows-host-rewrite.md) §2.2–2.4. This file is the **ordered,
independently-shippable execution plan**, because the host is **live-validated** (GameStream + punktfunk/1,
NVENC + IDD-push on-glass) and Goal-1 rewires its session/config/dispatch flow — so every stage must
**preserve behavior**, compile + box-verify on its own, and be committed before the next starts. The plan's
own §14 makes the §1 preservation checklist a mandatory per-module assert contract; honour it.

## Why staged (not one big rewrite)

`main` is at parity and shipping. A monolithic rewrite would put the validated host in a broken
intermediate state for a long window and make a regression impossible to bisect. Each stage below is a
behaviour-preserving transform with its own verification, so a regression is caught at the stage that
introduced it.

## Stages (ordered; each = goal · files · risk · verify)

**Stage 1 — `HostConfig` foundation. ✅ DONE (this commit).**
`config.rs`: typed `HostConfig` parsed ONCE from env (`idd_push`/`encoder_pref`/`no_helper`/`force_helper`).
Migrated the two highest-churn dispatch reads onto it (`encode::windows_resolved_backend`,
`punktfunk1::should_use_helper`). Risk: low (env constant at runtime → identical behaviour). Verify: box
`cargo check --features nvenc`.

**Stage 2 — finish `HostConfig` + resolve-once.**
Migrate the remaining ~64 `env::var` sites onto `HostConfig` fields (esp. `PUNKTFUNK_IDD_PUSH` ×8,
`PUNKTFUNK_RENDER_ADAPTER`, `PUNKTFUNK_ZEROCOPY`, `PUNKTFUNK_SECURE_DDA`, `PUNKTFUNK_IDD_DEPTH`,
`PUNKTFUNK_NO_WGC`, the perf/debug flags). Linux vars (XDG/compositor) included for one config. Risk:
medium (must preserve each var's exact semantics — a flipped bool is a silent regression; assert per the §1
checklist). Verify: Linux + box build; `grep env::var` should reach ~0 outside `config.rs`.

**Stage 3 — `SessionPlan` (the single biggest clarity lever, plan §2.4).**
Resolve `display/capture/topology/encoder/format/hdr/bit_depth` ONCE from `HostConfig` into a typed
`SessionPlan`; replace the 3-place dispatch (`capture_virtual_output`, `should_use_helper`/`virtual_stream`,
`windows_resolved_backend`) with reads off the plan. Fixes the capture/encode backend-disagreement bug
class. Risk: medium-high (rewires the deployed decision). Verify: box build + on-glass re-test (NVENC +
IDD-push + a mode switch).

**Stage 4 — `SessionContext` + `SessionFactory`/`Session`.**
Bundle the 12–13-arg `#[allow(too_many_arguments)]` signatures into `SessionContext`; `SessionFactory.build()`
owns the RAII chain `vdm.lease(mode) → open_capturer(vout, fmt) → open_encoder(plan) → spawn pipeline`, with
`Session::drop` the ONLY teardown path. Risk: high (teardown ordering — the §1 RAII asserts are mandatory).
Verify: box build + on-glass (connect/disconnect/reconnect, no leaked monitors/threads).

**Stage 5 — seam-trait tightenings (plan §2.3).**
`Capturer::open_capturer(vout, want: OutputFormat)` takes the format IN (kills the
`capture → encode::windows_resolved_backend()` back-reference recomputed in `dxgi.rs`); HDR/release become
`VirtualLease` methods (session glue names no concrete backend, contains no `unsafe`); optional encoder
features move to `EncoderCaps`. Risk: medium. Verify: box build + on-glass.

**Stage 6 — `src/windows/` tree (cfg-sprawl confinement, plan §2.2).**
Move the Windows backends under `src/windows/` + `capture/windows/`, `encode/windows/`, `inject/windows/`,
`audio/windows/`, `vdisplay/windows.rs` behind one `#[cfg(windows)] mod windows;` seam. Pure file move +
mod/use-path updates — behaviour-identical. Risk: low-but-huge (dozens of files; compile-verify catches all).
Do LAST so the earlier semantic stages don't fight path churn. Verify: Linux + box build.

## Guardrails (mandatory, plan §14)

- Each stage is its own commit; box-verify before moving on.
- Stages 3–5 touch the deployed path → **on-glass re-test** (NVENC + IDD-push, a mode switch, a
  connect/disconnect cycle) before the next stage.
- Preserve every `PUNKTFUNK_*` var's exact semantics; when in doubt, assert old==new at the call site.