Rename chatmodes to agents

[Copilot]

Pull Request

Summary

GitHub renamed "Chat Modes" to "Agents" in October 2025. IntelliJ requires the new naming convention (.github/agents/*.agent.md), while VS Code supports both.

Changes:

• New .github/agents/ directory with Developer.agent.md, Tester.agent.md, CodeReviewer.agent.md
• Excluded Planner/Documentation agents — VS Code now ships these built-in
• Deprecated .github/chatmodes/ — kept for backward compatibility
• Updated all documentation referencing agents vs deprecated chatmodes

Links

• Plan/TODO item: Issue docs: streamline copilot setup check prompt Phase 1 #11
• ADR/PRD/design doc: N/A — naming convention change only

Quality & Policy Checks

• Branch/PR rules followed (see .github/copilot-instructions.md)
• Tests added/updated; critical paths & errors at 100% (see Quality Policy)
• Docs updated (if applicable)
• Security and privacy considerations noted

Screenshots / Demos (optional)

N/A

Notes for Reviewers

• The new agent files are adapted from existing chatmode files with naming/terminology updates
• Fixed a duplicate search tool entry in Developer.agent.md that existed in the original chatmode
• recommendations.md and plans/TODO.md retain chatmode references in historical context with deprecation notes

Original prompt

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This section details on the original issue you should resolve

<issue_title>Chat modes have been renamed to Agents</issue_title>
<issue_description>See https://github.blog/changelog/2025-10-28-custom-agents-for-github-copilot/, chatmodes are now called agents.

This requires changes in the naming of the example agents (.github/chatmodes/xyz.chatmode.md -> .github/agents/xyz.agent.md) as well as adjustments of some readme files.</issue_description>

<agent_instructions>Implement as described. Deprecate the chatmodes and add agents. </agent_instructions>

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

@TonyCap I just tested around in my IDE's: VS Code seems to be able to handle the old naming as well, but in Intellij, it only works when the directory is called "agents" and the agent ends on `.agent.md`

VS Code in comparison:

@pidster Open question: do we retain chatmodes and mark it as deprecated, then *add* the agents subdirectory? @pidster VSC is now shipping with a Planner and a Documentation agent - so would we omit those in the new dir, or present them as alternatives? @TonyCap > VSC is now shipping with a Planner and a Documentation agent - so would we omit those in the new dir, or present them as alternatives?

Under these circumstances, I think it makes sense that if we decide keep the old chatmodes, marked as deprecated to then omit Planner and Documentation in the new directory.</comment_new>
<comment_new>@amv20
I would also go with: Retain what we have, mark it as deprecated and then define the new Agents we see with the new baseline of existing Planner and Documentation agents from GH. </comment_new>
<comment_new>@pidster
OK, I concur. That's +2 for keeping & deprecating.</comment_new>

• Fixes Chat modes have been renamed to Agents #12

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