Enhance Copilot instructions with build timing, CI/CD details, and troubleshooting

[Copilot]

Expands .github/copilot-instructions.md to reduce AI assistant exploration overhead and build failures.

Build Instructions

• Added timing expectations: 30-60 min native libs, 2-5 min APK, 15-25 min CI
• Documented environment setup (ANDROID_NDK_ROOT path variations)
• Added single-arch build shortcut: scripts/ndk-make.sh armeabi-v7a
• Common issues: missing NDK, uninitialized submodules, Gradle wrapper validation

Repository Structure

• Expanded with package paths (org.thoughtcrime.securesms.*, com.b44t.messenger.*, chat.delta.rpc.*)
• Documented generated code locations (don't edit chat.delta.rpc.*)
• Added script purposes (ndk-make.sh, install-toolchains.sh, generate-rpc-bindings.sh)

CI/CD Workflows

• Documented preview APK workflow: builds armeabi-v7a only, uses FOSS flavor
• Added validation requirements: Fastlane metadata, Gradle wrapper, --no-daemon flag

New Sections

• Validation checks: When to rebuild native libs vs. when not to
• Dependencies/Constraints: Java 8 compatibility, SDK 36, ProGuard always-on
• JSON-RPC bindings: Regeneration via ./scripts/generate-rpc-bindings.sh

Fixes

• Target SDK: 35 → 36 (matches build.gradle)
• Test durations: 1-3 min unit, 10-30 min instrumented

File size: ~1,400 words (within 2-page best practice limit)

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• gh.io
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node /home/REDACTED/work/_temp/ghcca-node/node/bin/node --enable-source-maps /home/REDACTED/work/_temp/copilot-developer-action-main/dist/index.js (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

---

This section details on the original issue you should resolve

<issue_title>✨ Set up Copilot instructions</issue_title>
<issue_description>Configure instructions for this repository as documented in Best practices for Copilot coding agent in your repository.

</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes ✨ Set up Copilot instructions #117

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