docs: decide minimum Android API level (34) and refresh README (session 0014)

Maintainer decision: minimum supported Android API is 34 (Android 14),
matching the already-fixed compile/target SDK exactly (DECISIONS.md
ADR-029) — the last remaining open item in ARCHITECTURE.md §15. Applied to
android/'s :app/:hardware/:ui modules (minSdk 26 -> 34); rebuilt and
re-tested, zero failures.

README.md refreshed to reflect the project's actual current state: capture
count, decision count, the three previously-open architecture questions now
resolved (Hilt, minimum API, Find My Buds Case scope), and the Android app
scaffolding that now exists under android/.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01V2WfHWj4DFbq79FSae5KdV

Author: tedsluis

ARCHITECTURE.md

@@ -31,9 +31,9 @@ Communication happens over two transports:
   proprietary RFCOMM traffic — not confirmed, no HID report content has been captured or decoded.
   Not treated as a confirmed transport for this app's own use until decoded.
 
-Compile/target SDK: API 34 (Android 14). Minimum supported Android API: **TBD** — see
-the open question in §15; do not treat "API 34" as if it already answered that. Primary
-reference OS: GrapheneOS, with compatibility maintained for stock AOSP-based ROMs.
+Compile/target/minimum SDK: **API 34 (Android 14)** — decided 2026-09-13, `DECISIONS.md` ADR-029;
+see §15's "already decided" list. Primary reference OS: GrapheneOS, with compatibility maintained
+for stock AOSP-based ROMs.
 
 ```
 ┌──────────────────────────────────────────────────────┐
@@ -529,18 +529,6 @@ undecided (see §15's "Already decided, not open" list, updated to match).
 
 > Move to `DECISIONS.md` once decided, following the ADR template.
 
-- [ ] Minimum supported Android API level: compile/target SDK is set at API 34
-      (Android 14), but the minimum SDK for broader AOSP-ROM compatibility is
-      not yet fixed. This is not blocked on a single API, so "TBD" here does
-      not mean unplanned: the generic battery broadcast (§4 option 0,
-      `BluetoothDevice.ACTION_BATTERY_LEVEL_CHANGED`) requires **API 31+**,
-      but §4's options 1–4 (Fast Pair advertisement, Message Stream, HFP,
-      GATT) are the confirmed primary paths and do not depend on API 31 — so a
-      lower min API (e.g. API 26 for `CompanionDeviceManager`, ADR-005) is not
-      blocked by option 0's availability, which simply degrades gracefully to
-      "unavailable on this API level, other options still work." The exact
-      floor still depends on which other BLE/Bluetooth APIs (foreground
-      service types, etc.) turn out to be required.
 - [ ] Added 2026-08-14: is the observed Bluetooth HID surface (§1) architecturally relevant to
       `:hardware`/`BudsTransport` — i.e. does any control feature this app needs actually route
       through HID reports rather than RFCOMM/GATT — or is it exclusively used by parts of the
@@ -561,7 +549,11 @@ undecided (see §15's "Already decided, not open" list, updated to match).
 > **dependency injection — Hilt** (see §10, `DECISIONS.md` ADR-028, decided
 > 2026-09-13); **Find My Buds Case/"both simultaneously" — out of scope for v1**
 > (`PROJECT.md` non-goals, `DECISIONS.md` ADR-027, decided 2026-09-13) — Left/Right
-> ring is unaffected and already implemented.
+> ring is unaffected and already implemented; **minimum supported Android API level
+> — API 34 (Android 14), same as compile/target SDK** (§1, `DECISIONS.md` ADR-029,
+> decided 2026-09-13) — no lower-API compatibility path is pursued; `CompanionDeviceManager`
+> (API 26, ADR-005) and the generic battery broadcast (API 31, §4 option 0) are both
+> trivially satisfied at this floor.
 
 ## 16. Attribution
 

DECISIONS.md

@@ -1417,5 +1417,34 @@ motivated this).
   open. Every future module needing a dependency graph entry uses Hilt's `@Inject`/`@Provides`
   conventions rather than a hand-rolled locator.
 
+## ADR-029 — Minimum supported Android API level: API 34 (Android 14)
+
+- **Date**: 2026-09-13
+- **Status**: Accepted
+- **Context**: `ARCHITECTURE.md` §15 left the minimum supported Android API level open — compile/
+  target SDK was already fixed at API 34 (Android 14), but how far down the minimum should go for
+  broader AOSP-ROM compatibility was undecided. The open item itself noted this wasn't blocked on a
+  single API: the generic battery broadcast (`ARCHITECTURE.md` §4 option 0) needs API 31+, but the
+  confirmed primary battery/ANC/EQ paths (Fast Pair advertisement, Message Stream, HFP, GATT) don't
+  depend on it, and `CompanionDeviceManager` (`DECISIONS.md` ADR-005) only needs API 26. The
+  maintainer decided directly, in conversation, that the minimum should simply match the
+  already-fixed compile/target SDK rather than support a wider, lower floor.
+- **Options considered**:
+  - A lower minimum (e.g. API 26, the floor `CompanionDeviceManager` itself needs) for broader
+    AOSP-ROM/older-device compatibility, accepting that API 31's generic battery broadcast (a cheap
+    supplementary check, not a required mechanism) degrades gracefully below that version.
+  - **API 34 (Android 14), matching compile/target SDK exactly** — chosen. Simplest option: no
+    version-gated code paths anywhere in the app, and this project's primary reference platform
+    (GrapheneOS, `ARCHITECTURE.md` §1) tracks current Android releases closely, so a lower floor
+    buys little real compatibility benefit for this project's actual user base.
+- **Decision**: minimum supported Android API level is **34 (Android 14)**, identical to
+  compile/target SDK. No lower-API compatibility path is pursued.
+- **Consequences**: `ARCHITECTURE.md` §1/§15 updated to record this as decided, not open. The
+  Android Gradle project's `minSdk` is set to 34 across every module that declares one (`:app`,
+  `:hardware`, `:ui`) — simpler than the API-26 floor used provisionally before this decision, since
+  every Bluetooth/battery mechanism this project relies on is available well below API 34 anyway.
+  This forecloses running on older Android versions/ROMs that can't be updated past API 33, a
+  deliberate trade-off given this project's GrapheneOS-first target.
+
 ---
 https://github.com/tedsluis/opencontrolpixelbudspro2/blob/main/DECISIONS.md - https://tedsluis.github.io/opencontrolpixelbudspro2/DECISIONS

README.md

@@ -3,13 +3,14 @@
 An independent, open-source Android app to fully control the **Google Pixel Buds
 Pro 2** without the official Pixel Buds app or Google Play Services.
 
-> **Status:** protocol-reconstruction phase. There is no application code yet — no
-> Gradle project or module skeleton has been created (see `TODO.md` Phase 4). The
-> protocol knowledge itself, however, has matured well beyond "early research": ANC
-> mode switching, Find My Buds (Left/Right), battery reporting (via HFP), and the
-> equalizer's live-write path are all confirmed 🟢 FACT and implementation-ready
-> (`PROTOCOL.md`, `DECISIONS.md`). See `TODO.md` for the current task list and
-> readiness assessment.
+> **Status:** protocol reconstruction is mature, and Android app development has begun. ANC mode
+> switching, Find My Buds (Left/Right), battery reporting (via HFP), and the equalizer's live-write
+> path are all confirmed 🟢 FACT and implementation-ready (`PROTOCOL.md`, `DECISIONS.md`). A real,
+> building, unit-tested Android Studio project now exists at [`android/`](./android) — five Gradle
+> modules, ANC's `FrameEncoder`/`FrameDecoder` implemented and tested against real capture bytes, a
+> working Hilt-wired composition root — but it has **no UI screens for real device control yet** and
+> has **never been run against real Pixel Buds hardware** (see `TODO.md` Phase 4 for exactly what's
+> done vs. still open).
 
 > ## ⚠️ Disclaimer: hardware risk
 >
@@ -47,26 +48,37 @@ the Pixel Buds Pro 2 first has to be reconstructed through Bluetooth traffic
 analysis and reverse engineering of the Android APK. That knowledge is then used
 to design, implement, test, and document a native Android app.
 
-## Current state (2026-09-08)
+## Current state (2026-09-13)
 
-- **Captures:** 42 registered sessions (`CAP-001`–`CAP-042`), most analyzed and a handful still
-  planned — see `CAPTURE_BLUETOOTH_HCI_SNOOP.md` §9's Capture Index.
+- **Captures:** 52 registered sessions (`CAP-001`–`CAP-052`), most analyzed and a handful still
+  planned — see `CAPTURE_BLUETOOTH_HCI_SNOOP.md` §9's Capture Index. A full, independent,
+  non-sampled re-derivation of every finding from an earlier full-catalog review found the core
+  protocol-decode content held up with zero errors (`ai-sessions/0012_CROSSCHECK_RESULT_2026_09_12.md`).
 - **APK analysis:** one companion-app version fully pulled, decompiled, and analyzed
   (`v1.0.955078536-10253511`) — see `reverse-engineering/APK_VERSIONS.md`. DLCI 0x04/0x08's own
   transport code was not found anywhere in it (`DECISIONS.md` ADR-025) — both channels are
   implemented from wire-capture evidence alone, not by decompiled-code cross-reference.
-- **Decisions:** 25 recorded architecture/protocol decisions (`DECISIONS.md`), every
-  🟢 FACT promotion in `PROTOCOL.md` traceable to an explicit maintainer sign-off.
+- **Decisions:** 29 recorded architecture/protocol decisions (`DECISIONS.md`), every
+  🟢 FACT promotion in `PROTOCOL.md` traceable to an explicit maintainer sign-off. The three
+  previously-open architecture questions are now all decided: dependency injection is **Hilt**
+  (ADR-028), minimum supported Android API is **34/Android 14**, matching compile/target SDK
+  (ADR-029), and Find My Buds for the Case/"both simultaneously" is an explicit, permanent v1
+  non-goal (ADR-027, Zero-GMS scope limit — see `PROJECT.md`).
 - **Confirmed and implementation-ready:** ANC/Transparency/Adaptive mode switching,
   Find My Buds (Left/Right), battery reporting (HFP), the equalizer's live-write
   path, touch-controls top-level toggle and press-and-hold assignment, mono audio,
-  multipoint, volume EQ, volume balance, and the "Bud return" case sound.
+  multipoint, volume EQ, volume balance (including its Left/Right polarity, ADR-026),
+  and the "Bud return" case sound.
 - **Still open:** touch-controls' head-gestures and ANC-mode-rotation sub-features,
-  in-ear detection, EQ preset persistence semantics, Find My Buds for
-  the case (a Zero-GMS scope question, not just a research gap), and per-component
+  in-ear detection, EQ preset persistence semantics, and per-component
   serial-number reading.
-- **Not started:** the Android app itself — no Gradle project exists in this
-  repository yet.
+- **App development has started** — see [`android/`](./android): five Gradle modules
+  (`:app`, `:ui`, `:domain`, `:data`, `:hardware`), a Hilt-wired `:app` composition root, and ANC's
+  `FrameEncoder`/`FrameDecoder` implemented and unit-tested against real, `tshark`-extracted capture
+  bytes (`./gradlew assembleDebug test` builds a real debug APK, all unit tests passing). **Not yet
+  done:** any UI screen for actually controlling the Buds, a real `BluetoothSocket`-backed transport
+  verified against hardware, and EQ/Battery/Find-My-Buds codecs (`:data` has ANC only so far) — see
+  `TODO.md` Phase 4 for the exact, up-to-date checklist.
 
 ## Approach
 
@@ -143,11 +155,11 @@ humans and AI coding assistants working on it:
 | `AI_SESSION_LOG_PROCEDURE.md` | Naming scheme, category vocabulary, and numbering discipline for logging AI-agent prompts/results into `ai-sessions/` |
 | `ai-sessions/INDEX.md` | Registry of every logged AI-agent prompt/result pair under `ai-sessions/` — check before assigning the next number |
 | `scripts/lint_docs.py` | Grep-based doc lint (dead filenames, unregistered IDs, stale project name) — run before committing a doc change |
+| `android/` | The Android Studio project itself (five Gradle modules: `:app`, `:ui`, `:domain`, `:data`, `:hardware`) — see the "Current state" section above for what's implemented so far |
 
 ## Target platform
 
-- Compile/target SDK: API 34 (Android 14)
-- Minimum supported Android API: **TBD** (see `ARCHITECTURE.md` §15)
+- Compile/target/minimum SDK: **API 34 (Android 14)** — `DECISIONS.md` ADR-029
 - Primary reference OS: GrapheneOS, with compatibility maintained for stock
   AOSP-based ROMs
 

TODO.md

@@ -17,7 +17,7 @@ nothing here is a second copy of that detail, only a pointer plus the reasoning
      current list. Per `AGENTS.md` §6 this step can only be done by the maintainer, not an agent.
    - ~~DI approach (Hilt vs. manual) — Phase 4.~~ **Resolved 2026-09-13: Hilt** (`DECISIONS.md`
      ADR-028).
-   - Minimum Android API level — Phase 5.
+   - ~~Minimum Android API level — Phase 5.~~ **Resolved 2026-09-13: API 34** (`DECISIONS.md` ADR-029).
    - ~~Find My Buds Case/"both simultaneously" — whether to accept a Google Find Hub/account-mediated
      fallback for this one sub-feature or ship v1 without local Case-ring support (`PROTOCOL.md` §6,
      Behavior) — a genuine Zero-GMS scope trade-off, not a research gap; no capture or static
@@ -525,8 +525,9 @@ lower priority than finishing ANC/Battery/EQ):**
       (differing Android version and/or OEM, including GrapheneOS as the
       primary reference target per `ARCHITECTURE.md` §1)
 - [ ] Update `README.md` with build instructions once the app builds
-- [ ] Decide minimum supported Android API level and record it in
-      `DECISIONS.md` (currently open, see `ARCHITECTURE.md` §15)
+- [x] **Decide minimum supported Android API level — resolved 2026-09-13: API 34 (Android 14),
+      matching compile/target SDK** (`DECISIONS.md` ADR-029, `ARCHITECTURE.md` §1/§15). Applied to
+      `android/`'s `:app`/`:hardware`/`:ui` modules (`minSdk = 34`).
 - [ ] Decide multi-device (multiple paired Buds) support for v1 and record it
       in `PROJECT.md` scope + `DECISIONS.md` (currently open, see
       `ARCHITECTURE.md` §15)

ai-sessions/0014_MAINTENANCE_PROMPT_2026_09_13.md

@@ -0,0 +1,50 @@
+# 0014_MAINTENANCE_PROMPT_2026_09_13.md — Decide minimum Android API level, refresh README.md, commit and push
+
+**Number:** 0014
+**Category:** MAINTENANCE
+**Date:** 2026-09-13
+**Title:** Decide minimum Android API level, refresh README.md's project status, commit and push
+
+---
+
+## Mandatory reading order
+
+Per `AGENTS.md` §0.1 and `AI_SESSION_LOG_PROCEDURE.md` §8: `AGENTS.md`, `PROJECT.md`,
+`PROJECT_RULES.md`, and `DECISIONS.md` in full at minimum before any other action, plus
+`ARCHITECTURE.md` (§1/§15 specifically, for the open minimum-API question this prompt resolves),
+`TODO.md` (Phase 5's matching checklist item), and `README.md` (the file being updated) — all
+already read in full earlier in this same conversation, still current.
+
+## Task (verbatim, as given by the maintainer in chat, translated from Dutch)
+
+> 1) I decide that Android 14 is the minimum version. Process this decision in the relevant files.
+> 2) Update the current state of the project in README.md.
+> 3) Commit and push the files. If possible, make separate commits per prompt.
+
+This is a direct continuation of the same chat session that authored and resolved
+`ai-sessions/0013_FEATURE_PROMPT_2026_09_13.md`/`ai-sessions/0013_FEATURE_RESULT_2026_09_13.md` —
+that session's own Phase 5 (`TODO.md`'s "Decide minimum supported Android API level" item,
+`ARCHITECTURE.md` §15) is what this prompt closes.
+
+## Scope
+
+1. Record the minimum-Android-API-level decision (Android 14 / API 34, matching this project's
+   already-fixed compile/target SDK) as a `DECISIONS.md` ADR, per `AGENTS.md` §6/§15 — this session
+   has the maintainer's direct, explicit decision in-conversation, so no proposal/sign-off gate
+   applies here (unlike `0013`'s Phase 4/5/6 items, which were AI-drafted proposals). Apply the
+   decision to every relevant document (`ARCHITECTURE.md`, `TODO.md`) and to the actual Android
+   project (`android/`'s `:app`/`:hardware`/`:ui` `minSdk`), then rebuild/re-test to confirm nothing
+   regresses.
+2. Update `README.md`'s "Current state" section (and any other stale summary text, e.g. the top
+   status callout and the "Target platform" section) to reflect the project's actual current state —
+   captures, decisions, protocol readiness, and, new since the last README update, the Android app
+   scaffolding itself (five Gradle modules, ANC codec implemented/tested, Hilt wired, minimum API
+   decided).
+3. Commit and push. Per the maintainer's own instruction, make separate commits per distinct prior
+   "prompt" where practical, rather than one bundled commit — applied here as: session `0012`'s own
+   files, session `0013`'s own files (including the three decisions approved earlier this same chat
+   turn and the new `android/` project), and this prompt's own files (minSdk decision + README
+   refresh), as three separate commits, in that order, followed by a single push.
+
+---
+https://github.com/tedsluis/opencontrolpixelbudspro2/blob/main/ai-sessions/0014_MAINTENANCE_PROMPT_2026_09_13.md - https://tedsluis.github.io/opencontrolpixelbudspro2/ai-sessions/0014_MAINTENANCE_PROMPT_2026_09_13