Replace upstream terminology with reference implementation

Rebase the topic branch onto current main and preserve the original intent:
replace "upstream" naming with "reference implementation" across the repo.

- Update docs, prompts, workflows, and release automation wording
- Remove legacy upstream-sync assets superseded by reference-impl-sync assets
- Update references in tests and project guidance content
- Keep behavior aligned while clarifying terminology
- Apply Spotless formatting updates in touched Java test files

.github/copilot-instructions.md

@@ -9,7 +9,7 @@ These instructions guide GitHub Copilot when assisting with this repository. The
 - **Tech Stack**: Java 17+, Maven, Jackson for JSON, JUnit for testing
 - **Purpose**: Provide a Java SDK for programmatic control of GitHub Copilot CLI
 - **Architecture**: JSON-RPC client communicating with Copilot CLI over stdio
-- **Key Goals**: Maintain parity with upstream .NET SDK while following Java idioms
+- **Key Goals**: Maintain parity with reference implementation .NET SDK while following Java idioms
 
 ## Build & Test Commands
 
@@ -85,7 +85,7 @@ Tests use the official copilot-sdk test harness from `https://github.com/github/
 
 - **E2ETestContext** - Manages test environment with CapiProxy for deterministic API responses
 - **CapiProxy** - Node.js-based replaying proxy using YAML snapshots from `test/snapshots/`
-- Test snapshots are stored in the upstream repo's `test/snapshots/` directory
+- Test snapshots are stored in the reference implementation repo's `test/snapshots/` directory
 
 ## Key Conventions
 
@@ -217,7 +217,7 @@ Test method names are converted to lowercase snake_case for snapshot filenames t
 - **DO NOT** modify `target/` directory - this contains build artifacts
 - **DO NOT** edit `pom.xml` dependencies without careful consideration - this SDK has minimal dependencies by design
 - **DO NOT** change the Jackson version without testing against all serialization patterns
-- **DO NOT** modify test snapshots in `target/copilot-sdk/test/snapshots/` - these come from upstream
+- **DO NOT** modify test snapshots in `target/copilot-sdk/test/snapshots/` - these come from reference implementation
 - **DO NOT** alter the Eclipse formatter configuration in `pom.xml` without team consensus
 - **DO NOT** remove or skip Checkstyle or Spotless checks
 
@@ -299,12 +299,12 @@ The release process is automated via the `publish-maven.yml` GitHub Actions work
    - Converts the `## [Unreleased]` section to `## [version] - date`
    - Creates a new empty `## [Unreleased]` section at the top
    - Updates version comparison links at the bottom of CHANGELOG.md
-   - Injects the upstream SDK commit hash (from `.lastmerge`) as a `> **Upstream sync:**` blockquote in both the new `[Unreleased]` section and the released version section
+   - Injects the reference implementation SDK commit hash (from `.lastmerge`) as a `> **Reference implementation sync:**` blockquote in both the new `[Unreleased]` section and the released version section
 
 2. **Reference Implementation Sync Tracking**: Each release records which commit from the official `github/copilot-sdk` it is synced to:
    - The `.lastmerge` file is read during the release workflow
    - The commit hash is injected into `CHANGELOG.md` under the release heading
-   - Format: `> **Upstream sync:** [\`github/copilot-sdk@SHORT_HASH\`](link-to-commit)`
+   - Format: `> **Reference implementation sync:** [\`github/copilot-sdk@SHORT_HASH\`](link-to-commit)`
 
 3. **Documentation Updates**: README.md and jbang-example.java are updated with the new version.
 
@@ -316,3 +316,4 @@ The release process is automated via the `publish-maven.yml` GitHub Actions work
 5. **Rollback**: If the release fails, the documentation commit is automatically reverted
 
 The workflow is triggered manually via workflow_dispatch with optional version parameters.
+

.github/prompts/agentic-merge-reference-impl.prompt.md

@@ -56,7 +56,7 @@ This writes a `.merge-env` file used by the other scripts. It outputs:
 - The reference-impl dir path
 - A short log of reference implementation commits since `.lastmerge`
 
-## Step 2: Analyze Upstream Changes
+## Step 2: Analyze reference implementation Changes
 
 Run the diff script for a detailed breakdown by area:
 
@@ -96,7 +96,7 @@ For each change in the reference implementation diff, determine:
 
 ### Key Files to Compare
 
-| Upstream (.NET)                    | Java SDK Equivalent                                    |
+| reference implementation (.NET)                    | Java SDK Equivalent                                    |
 |------------------------------------|--------------------------------------------------------|
 | `dotnet/src/Client.cs`             | `src/main/java/com/github/copilot/sdk/CopilotClient.java` |
 | `dotnet/src/Session.cs`            | `src/main/java/com/github/copilot/sdk/CopilotSession.java` |
@@ -121,7 +121,7 @@ Before modifying any code:
 2. **Identify the Java equivalent approach** - Don't replicate C# patterns; find the idiomatic Java way
 3. **Check for existing abstractions** - The Java SDK may already have mechanisms that differ from .NET
 4. **Preserve backward compatibility** - Existing API signatures should not break unless absolutely necessary
-5. **When in doubt, match existing code** - Follow what's already in the Java SDK, not the upstream
+5. **When in doubt, match existing code** - Follow what's already in the Java SDK, not the reference implementation
 
 ### Commit Changes Incrementally
 
@@ -181,8 +181,8 @@ After porting implementation changes, **always check for new or updated tests**
 
 ```bash
 cd "$TEMP_DIR/copilot-sdk"
-git diff "$LAST_MERGE_COMMIT"..origin/main --stat -- dotnet/test/
-git diff "$LAST_MERGE_COMMIT"..origin/main --stat -- test/snapshots/
+git diff "$LAST_REFERENCE_IMPL_COMMIT"..origin/main --stat -- dotnet/test/
+git diff "$LAST_REFERENCE_IMPL_COMMIT"..origin/main --stat -- test/snapshots/
 ```
 
 ### Port Test Cases
@@ -196,7 +196,7 @@ For each new or modified test file in `dotnet/test/`:
 
 ### Test File Mapping
 
-| Upstream Test (.NET)        | Java SDK Test                                          |
+| reference implementation Test (.NET)        | Java SDK Test                                          |
 |-----------------------------|--------------------------------------------------------|
 | `dotnet/test/AskUserTests.cs`  | `src/test/java/com/github/copilot/sdk/AskUserTest.java`  |
 | `dotnet/test/HooksTests.cs`    | `src/test/java/com/github/copilot/sdk/HooksTest.java`    |
@@ -209,7 +209,7 @@ New test snapshots are stored in `test/snapshots/` in the reference implementati
 
 If tests fail with errors like `TypeError: Cannot read properties of undefined`, the test harness may not yet support the new RPC methods. In this case:
 
-1. **Mark tests as `@Disabled`** with a clear reason (e.g., `@Disabled("Requires test harness update with X support - see upstream PR #NNN")`)
+1. **Mark tests as `@Disabled`** with a clear reason (e.g., `@Disabled("Requires test harness update with X support - see reference implementation PR #NNN")`)
 2. **Document the dependency** in the test class Javadoc
 3. **Enable tests later** once the harness is updated
 
@@ -403,7 +403,7 @@ Before finishing:
 - [ ] New branch created from `main`
 - [ ] Copilot CLI updated to latest version
 - [ ] README.md updated with minimum CLI version requirement
-- [ ] Upstream repository cloned
+- [ ] reference implementation repository cloned
 - [ ] Diff analyzed between `.lastmerge` commit and HEAD
 - [ ] New features/fixes identified
 - [ ] Changes ported to Java SDK following conventions
@@ -437,3 +437,4 @@ Before finishing:
 - Uses JUnit 5 for testing
 - **Java SDK design decisions take precedence over reference implementation patterns**
 - **Adapt reference implementation changes to fit Java idioms, not the other way around**
+