Fix part of #6106: Add Release Playbook wiki page

wiki/Release-Playbook.md

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+# Release Playbook
+
+This page is the step-by-step coordinator guide for Oppia Android releases using the automated
+release pipeline. For conceptual background on any step, see the
+[App and Feature Release Process](app-and-feature-release-process.md) wiki page. For manual
+fallback procedures when automation fails, see the
+[In-Depth Release Reference](In-Depth-Release-Reference.md).
+
+---
+
+## Table of Contents
+
+1. [Weekly alpha release](#1-weekly-alpha-release)
+2. [Changelog review](#2-changelog-review)
+3. [Production release](#3-production-release)
+4. [Staged rollout](#4-staged-rollout)
+5. [Weekly coordinator checklist](#5-weekly-coordinator-checklist)
+
+---
+
+## 1. Weekly Alpha Release
+
+The `auto_release_alpha.yml` workflow fires automatically every **Tuesday at 03:30 UTC**. It
+finds the latest passing commit on `develop`, tags it as `latest-alpha`, and dispatches
+`build_and_sign.yml`. The coordinator's job starts at the approval gate.
+
+### Steps
+
+- [ ] **Approve the build** — Navigate to Actions → `build_and_sign.yml` run → approve in the
+  `oppia-android-release-env` gate.
+- [ ] **Copy the GCS path** — After the build completes, copy the signed AAB path from the job
+  summary (format: `gs://oppia-android-alpha-releases/…/*.aab`).
+- [ ] **Distribute to QA** — Trigger `deploy_to_firebase.yml` with the GCS path above.
+- [ ] **Await QA sign-off** — Notify the alpha tester group and wait for their confirmation.
+- [ ] **Deploy to Play Console** — Trigger `deploy_to_play_console.yml`:
+  | Input | Value |
+  |---|---|
+  | `gcs_aab_path` | GCS path from above |
+  | `track` | `alpha` |
+  | `rollout_fraction` | `1000` (100% for alpha track) |
+
+> If `auto_release_alpha.yml` exits with an error or finds no passing commit, see the
+> [In-Depth Release Reference](In-Depth-Release-Reference.md) for manual fallback steps.
+
+---
+
+## 2. Changelog Review
+
+`generate_changelog.yml` opens a PR to `develop` automatically when `version.bzl` is updated
+with a new `MINOR_VERSION`. It can also be triggered manually via `workflow_dispatch`.
+
+### Steps
+
+- [ ] Open the changelog PR created by the workflow.
+- [ ] Review the AI-generated release notes in `config/changelogs/{version}.md` (and any
+  flavor-specific overrides such as `{version}_alpha.md` or `{version}_beta.md`).
+- [ ] Edit the release notes if the AI summary needs adjustment before merging.
+- [ ] Merge the changelog PR into `develop`.
+
+---
+
+## 3. Production Release
+
+Follow this checklist for a full beta or production (GA) release.
+
+### Pre-release
+
+- [ ] Confirm `MINOR_VERSION` is bumped in `version.bzl` and the changelog PR is merged (§2).
+- [ ] Cut the release branch from `develop` HEAD:
+  ```
+  git checkout -b release-0.X upstream/develop
+  git push upstream release-0.X
+  ```
+
+### Build & sign
+
+- [ ] Trigger `build_and_sign.yml`:
+  | Input | Value |
+  |---|---|
+  | `flavor` | `beta` or `ga` |
+  | `source_ref` | `release-0.X` |
+- [ ] Approve the run in the `oppia-android-release-env` gate.
+- [ ] Copy the signed AAB GCS path from the job summary.
+
+### QA
+
+- [ ] Trigger `deploy_to_firebase.yml` with the GCS path.
+- [ ] Notify QA testers and await sign-off.
+- [ ] If QA fails: land the fix on `develop`, cherry-pick to `release-0.X`, rebuild from
+  Build & sign above.
+
+### Deploy
+
+- [ ] Trigger `deploy_to_play_console.yml`:
+  | Input | Value |
+  |---|---|
+  | `gcs_aab_path` | GCS path from above |
+  | `track` | `beta` or `production` |
+  | `rollout_fraction` | `100` (10% initial rollout — see §4) |
+
+---
+
+## 4. Staged Rollout
+
+After the initial deployment, progressively increase the rollout using `update_rollout.yml`.
+Monitor Firebase Crashlytics between each step; halt and investigate if crash rates spike.
+
+| Day | `rollout_fraction` | Action |
+|---|---|---|
+| 0 | `100` | Initial deploy via `deploy_to_play_console.yml` |
+| 1 | `250` | Trigger `update_rollout.yml` after monitoring |
+| 3 | `500` | Trigger `update_rollout.yml` |
+| 7+ | `1000` | Trigger `update_rollout.yml` for full rollout |
+
+**Inputs for `update_rollout.yml`:**
+
+| Input | Value |
+|---|---|
+| `track` | `beta` or `production` |
+| `version` | e.g. `0.18` |
+| `rollout_fraction` | New fraction from the table above |
+
+---
+
+## 5. Weekly Coordinator Checklist
+
+Run through this checklist each week:
+
+- [ ] Check whether `auto_release_alpha.yml` completed successfully on Tuesday. If not,
+  consult the [In-Depth Release Reference](In-Depth-Release-Reference.md).
+- [ ] Check whether `pull_latest_lesson_versions.yml` opened a PR on Monday. If so, review
+  and merge the lesson-versions PR.
+- [ ] Check for any pending changelog PRs opened by `generate_changelog.yml` and merge them.
+- [ ] Review crash rates in Firebase Crashlytics and advance the rollout fraction if stable
+  (see §4).
+
+---
+
+*See also: [App and Feature Release Process](app-and-feature-release-process.md) ·
+[In-Depth Release Reference](In-Depth-Release-Reference.md) ·
+[Platform Parameters & Feature Flags](Platform-Parameters-&-Feature-Flags.md)*