## Status

**DRAFT — RFC only. Awaiting owner review BEFORE any bulk conversion.**
No Kotlin deleted, no Gossamer scaffolding generated, no behaviour
change.

Supersedes #96 (was titled "Tauri 2" — owner correction: Gossamer is the
estate target).

## Why

`android/` ships 7 Kotlin files + 3 `*.gradle.kts` files, all banned by
the
Hyperpolymath language policy. Two CI gates permanently red:

- `Check for Banned Languages`
(`.github/workflows/language-policy.yml:87-94`)
- `governance / Language / package anti-pattern policy` (estate-wide)

## What this PR contains

A single document — `docs/migrations/RFC-ANDROID-KOTLIN-TO-RUST.adoc` —
mapping every Kotlin component to its Gossamer replacement and proposing
a 9-PR landing sequence.

## Component mapping (one-line summary)

| Kotlin file | Replacement |
|---|---|
| `MainActivity.kt` | `NeurophoneMainActivity extends GossamerActivity`
|
| `NeurophoneService.kt` | Hand-written Java `Service` shim → JNI into
Rust |
| `BootReceiver.kt` | Hand-written Java `BroadcastReceiver` shim → JNI |
| `NativeLib.kt` | Delete; lives in
`crates/neurophone-android/src/lib.rs` |
| `NeurophoneAppWidget.kt` | Hand-written Java `AppWidgetProvider` shim
|
| `NeurophoneWidgetActions.kt` | Hand-written Java `BroadcastReceiver`
shim |
| `NeurophoneWidgetConfigureActivity.kt` | Java `Activity` shim (or
drop) |
| `*.gradle.kts` | Groovy `*.gradle` (matches Gossamer upstream) |

## Key structural finding

**Gossamer Android is webview-only today.** ROADMAP Phase 3 (Mobile)
lists Android as *Partially Implemented* — only `GossamerActivity` +
`GossamerBridge` exist upstream. The 7 platform-integration surfaces
neurophone needs (service, widget, receivers, sensors, intent dispatch,
prefs, deep-links) have **no upstream Gossamer support and no open
Gossamer issues**.

**Recommendation:** build all 7 downstream in neurophone's own
`android/`
tree as small Java shims that JNI immediately into Rust. Don't block
neurophone on Gossamer upstream PRs. Estimated total shim surface: < 250
LoC of Java vs. current 926 LoC of Kotlin.

## Estate precedent

- `panll` migrated `src-tauri/` → `src-gossamer/` (commit `598d537`,
  ADR-0001 in `b935727`). Webview UI unchanged; swapped `tauri` crate
  for `gossamer-rs`, `tauri.conf.json` for `gossamer.conf.json`,
  `cargo tauri build` for `deno task build` invoking the `gossamer` CLI.
- panll is **desktop only** — its migration did not exercise foreground
  service or home-screen widget surfaces; neurophone will be the first.

## Sub-PR sequence (proposed)

1. **This PR** — RFC only.
2. CI exemption for `android/**/*.java` (coordinated with
`hyperpolymath/standards`).
3. Gossamer scaffolding: `gossamer-rs` workspace dep,
`gossamer.conf.json`,
   `NeurophoneMainActivity` Java shim loading placeholder HTML.
4. Port `NativeLib` Kotlin → `crates/neurophone-android/src/lib.rs`.
5. Port `NeurophoneService` → Java shim + Rust impl.
6. Port `BootReceiver`.
7. Port widget triple (provider / actions / configure).
8. AffineScript UI compiled to JS, loaded by Gossamer webview.
9. Delete legacy Kotlin `android/` tree — both CI gates green.

PRs 2 & 3 sequenced; 4–7 parallelizable after 3; 8 needs 4; 9 gated on
all.

## Open questions for owner

1. **CI exemption scope** — estate-wide via `hyperpolymath/standards`
   or neurophone-local? Linchpin question.
2. **Estate governance** — who owns the cross-repo anti-pattern policy
   callable in standards?
3. **Widget config sacrifice** — acceptable to drop the configure
activity?
4. **Gradle DSL** — Groovy `*.gradle` (matches Gossamer upstream) or
   keep Kotlin `*.gradle.kts` under a separate exemption?
5. **Hardware test plan** — Oppo Reno 13 vs emulator + Termux?
6. **Upstream contribution** — build shims neurophone-local, or factor
   a `gossamer-android-services` companion as we go?

## Constraints honoured

- All new files MPL-2.0 SPDX.
- No new GitHub Actions added.
- No Deno/npm/TypeScript changes.

## Test plan

- [x] RFC document renders as AsciiDoc.
- [ ] Owner reviews component mapping for completeness.
- [ ] Owner picks CI-exemption scope (open Q1).
- [ ] Owner resolves Gradle DSL choice (open Q4).
- [ ] Sub-PR #2 (CI exemption) opens once approved.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

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