Add on-device Android port (lwc-core, lwc-android, Compose sample)

[RohitWaghire]

This add an Android as a first-class target: a Kotlin port of the SDK that runs
entirely on-device. Users sign in with their own ChatGPT subscription via the
device-code flow, tokens live in Android-Keystore-encrypted storage, and apps
stream Codex models billed to the user's plan - same model as the web SDK, but
with no server to host (the natural trust boundary for a native app, like the
Codex CLI itself).

No changes to the existing TS packages - everything lives in a new
android/ Gradle project.

Modules

• lwc-core - pure Kotlin/JVM engine miroring packages/core: device-code
  OAuth, token exchange/refresh, JWT claims, and /responses SSE streaming as
  a Flow<String>. Tests ported 1:1 from packages/core/test.
• lwc-android - Keystore-backed TokenStore, Custom Tab launcher,
  LoginWithChatGPT facade.
• sample - minimal Compose app: sign-in → device code → streamed chat.

Verification

• ./gradlew :lwc-core:test - 14/14 pass (JUnit ports of the TS oracles).
• Live end-to-end spike (./gradlew :lwc-core:run) passed against a real
  ChatGPT account: device login → model discovery → streamed gpt-5.5 reply.
• ./gradlew :sample:assembleDebug produces a working APK.

Notes for review

• Two wire-format requirements surfaced by the live run are encoded in
  CodexTransport.kt: /responses needs stream: true for SSE, and input
  must be a list of message items (a bare string gets
  400 {"detail":"Input must be a list"}). The TS core may want the same
  guard in normalizeResponsesBody someday.
• Kotlin transport behavior intentionally mirrors
  packages/core/src/codex-transport.ts; divergences are commented.

Happy to adjust structure/naming to fit the repo's conventions.

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[greptile-apps]

Greptile Summary

This PR adds a standalone Android port for Login with ChatGPT. The main changes are:

• New Android Gradle project with lwc-core, lwc-android, and sample modules.
• Kotlin/JVM core for device-code OAuth, token refresh, JWT parsing, Codex model listing, and SSE response streaming.
• Android facade with Keystore-backed encrypted token storage and Custom Tab verification launch.
• Compose sample app for sign-in, device-code polling, logout, and streamed chat.
• JVM tests covering Codex body normalization, URL mapping, client version handling, model parsing, and JWT helpers.

Confidence Score: 5/5

Safe to merge with low risk from the reviewed changes.

No blocking or non-blocking issues were found in the reviewed Android modules, core OAuth and transport logic, sample app, or tests. The earlier backup, Custom Tab launch, and custom-port concerns are addressed in the current diff.

No files require special attention.

T-Rex Logs

What T-Rex did

• The proof transcript was saved for review.
• The transcript shows java not found, javac not found, an empty JAVA_HOME, and a Gradle failure indicating JAVA_HOME is not set and no java command could be found in the PATH.
• Because the test task could not start in the sandbox, there is no evidence of a PR code failure.

_{Ran code and verified through T-Rex}

Important Files Changed

Filename	Overview
android/lwc-core/src/main/kotlin/com/opencoredev/loginwithchatgpt/CodexTransport.kt	Adds Codex request normalization, URL mapping, SSE streaming, and model-list extraction; no issues found.
android/lwc-core/src/main/kotlin/com/opencoredev/loginwithchatgpt/Device.kt	Adds device-code request, polling, token exchange, and wait-loop support; no issues found.
android/lwc-core/src/main/kotlin/com/opencoredev/loginwithchatgpt/OAuth.kt	Adds authorization-code exchange and refresh-token handling with dead-refresh error mapping; no issues found.
android/lwc-android/src/main/kotlin/com/opencoredev/loginwithchatgpt/android/KeystoreTokenStore.kt	Adds Keystore-backed encrypted token persistence with recovery from undecryptable restored preferences; no issues found.
android/lwc-android/src/main/kotlin/com/opencoredev/loginwithchatgpt/android/LoginWithChatGPT.kt	Adds the Android facade wiring device login, token storage, refresh, model listing, and streaming chat; no issues found.
android/lwc-android/src/main/kotlin/com/opencoredev/loginwithchatgpt/android/VerificationLauncher.kt	Adds Custom Tab launch support with the required new-task flag for application contexts; no issues found.
android/sample/src/main/AndroidManifest.xml	Adds internet permission and launcher activity with backups disabled for encrypted token safety; no issues found.
android/sample/src/main/kotlin/com/opencoredev/loginwithchatgpt/sample/MainActivity.kt	Adds a Compose sample covering login, polling, logout, and streamed chat; no issues found.
android/lwc-core/src/test/kotlin/com/opencoredev/loginwithchatgpt/CodexTransportTest.kt	Adds Kotlin tests for Codex body normalization, URL mapping, client versioning, and model parsing; no issues found.
android/lwc-core/src/test/kotlin/com/opencoredev/loginwithchatgpt/JwtTest.kt	Adds JWT decoding, account-id derivation, expiry, and user-profile tests; no issues found.

Sequence Diagram

%%{init: {'theme': 'neutral'}}%%
sequenceDiagram
participant App as Compose sample / app
participant Facade as LoginWithChatGPT
participant Core as lwc-core OAuth + Codex
participant Store as KeystoreTokenStore
participant Browser as Custom Tab
participant OpenAI as OpenAI / ChatGPT endpoints

App->>Facade: startDeviceLogin()
Facade->>Core: requestDeviceCode(config)
Core->>OpenAI: POST /deviceauth/usercode
OpenAI-->>Core: device_auth_id + user_code
Core-->>Facade: DeviceCode
Facade-->>App: DeviceCode
App->>Facade: openVerification(device)
Facade->>Browser: launch verification URL
Browser->>OpenAI: user enters code
loop until authorized or expired
    App->>Facade: poll(device)
    Facade->>Core: pollDeviceCode(config, device)
    Core->>OpenAI: POST /deviceauth/token
    OpenAI-->>Core: pending or authorization_code + PKCE
end
Facade->>Core: exchangeDeviceAuthorization(...)
Core->>OpenAI: POST /oauth/token
OpenAI-->>Core: access / refresh / id tokens
Facade->>Store: save(tokens)
App->>Facade: chat(body)
Facade->>Store: load()
Facade->>Core: ensureFreshTokens + codexResponses
Core->>OpenAI: "POST /backend-api/codex/responses stream=true"
OpenAI-->>Core: SSE text deltas
Core-->>App: "Flow<String> deltas"

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%%{init: {'theme': 'base', 'themeVariables': {"darkMode": true, "background": "#0d1117", "primaryColor": "#21262d", "primaryTextColor": "#e6edf3", "primaryBorderColor": "#8b949e", "lineColor": "#8b949e", "textColor": "#e6edf3", "edgeLabelBackground": "#161b22", "actorBkg": "#21262d", "actorBorder": "#8b949e", "actorTextColor": "#e6edf3", "actorLineColor": "#8b949e", "signalColor": "#8b949e", "signalTextColor": "#e6edf3", "noteBkgColor": "#373320", "noteBorderColor": "#d4a72c", "noteTextColor": "#f0e6c0", "labelBoxBkgColor": "#21262d", "labelBoxBorderColor": "#8b949e", "labelTextColor": "#e6edf3", "loopTextColor": "#e6edf3", "activationBkgColor": "#30363d", "activationBorderColor": "#8b949e"}}}%%
sequenceDiagram
participant App as Compose sample / app
participant Facade as LoginWithChatGPT
participant Core as lwc-core OAuth + Codex
participant Store as KeystoreTokenStore
participant Browser as Custom Tab
participant OpenAI as OpenAI / ChatGPT endpoints

App->>Facade: startDeviceLogin()
Facade->>Core: requestDeviceCode(config)
Core->>OpenAI: POST /deviceauth/usercode
OpenAI-->>Core: device_auth_id + user_code
Core-->>Facade: DeviceCode
Facade-->>App: DeviceCode
App->>Facade: openVerification(device)
Facade->>Browser: launch verification URL
Browser->>OpenAI: user enters code
loop until authorized or expired
    App->>Facade: poll(device)
    Facade->>Core: pollDeviceCode(config, device)
    Core->>OpenAI: POST /deviceauth/token
    OpenAI-->>Core: pending or authorization_code + PKCE
end
Facade->>Core: exchangeDeviceAuthorization(...)
Core->>OpenAI: POST /oauth/token
OpenAI-->>Core: access / refresh / id tokens
Facade->>Store: save(tokens)
App->>Facade: chat(body)
Facade->>Store: load()
Facade->>Core: ensureFreshTokens + codexResponses
Core->>OpenAI: "POST /backend-api/codex/responses stream=true"
OpenAI-->>Core: SSE text deltas
Core-->>App: "Flow<String> deltas"

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_{Reviews (3): Last reviewed commit: "Handle undecryptable token store after b..." | Re-trigger Greptile}