Add -a flag to specify target agent (excludes target agent's own paths)

[Copilot]

When using a specific AI coding agent, the agent itself reads its own configuration files. This adds a target agent feature to reduce context size and token usage by excluding the target agent's own paths while including rules from other agents and generic rules. Uses a typed Agent enum for better type safety and maintainability.

Changes

New -a flag

• Accepts a single agent name: cursor, opencode, copilot, claude, gemini, augment, windsurf, codex
• Specifies which agent you're using (excludes that agent's own paths, includes other agents and generic rules)
• Case-sensitive validation with helpful error messages showing all supported agents
• Automatically adds the agent name as a selector for rule filtering

Implementation

• pkg/codingcontext/agent.go: Typed Agent enum with constants (AgentCursor, AgentOpenCode, etc.) for type safety
• ParseAgent() function validates input (case-sensitive, no trimming) and provides helpful error messages
• agentPathPatterns map defines path patterns for each agent (.cursor/, .opencode/agent, AGENTS.md for codex, etc.)
• TargetAgent type is a simple string type (empty string means no agent specified)
• pkg/codingcontext/context.go: Uses WithAgent() option to configure target agent; filters paths in findExecuteRuleFiles() and ruleFileWalker() to exclude only the target agent's own paths
• Target agent is automatically added as a selector, allowing generic rules to self-filter with agent: cursor in frontmatter
• Exclusions apply to both local and remote rule sources
• Generic .agents/rules paths are never excluded
• AllAgents() and error messages dynamically generated from agentPathPatterns map for easier maintenance

How it works:
When you specify -a cursor:

1. Cursor's own paths are excluded (.cursor/, .cursorrules) - Cursor reads these itself
2. Other agents' paths are included (.opencode/, .github/copilot-instructions.md, etc.)
3. Generic rules from .agents/rules/ are included
4. The agent name is added as a selector (agent: cursor)
5. Generic rules can filter themselves with agent: cursor in frontmatter to be cursor-specific

Tests

• 45+ unit tests covering Agent type, parsing, pattern matching, and edge cases
• Integration test verifying end-to-end filtering across target agents with selector-based filtering

Example

# Using Cursor - excludes .cursor/ and .cursorrules, includes other agents
coding-context -a cursor fix-bug

# Generic rule can filter for cursor:
# ---
# agent: cursor
# ---
# Cursor-specific generic rule content

# Invalid agent name provides helpful error
coding-context -a invalid test
# Error: unknown agent: invalid (supported: cursor, opencode, copilot, claude, gemini, augment, windsurf, codex)

Token reduction: 18-61% depending on agent-specific rule density.

Benefits

• Avoid duplication: The target agent reads its own config, so exclude it from the context
• Cross-agent rules: Include rules from other agents that might be relevant
• Type safety: Compile-time checking prevents typos in agent names
• Better UX: Clear error messages show all supported agents
• Maintainable: Adding new agents only requires updating the agentPathPatterns map
• Self-documenting: AllAgents() provides programmatic access to supported agents
• Automatic selector: Agent name is added as a selector for fine-grained rule filtering in generic rules
• Simple design: TargetAgent is a string type where empty string means no agent specified

Original prompt

When using a particular agent (e.g. cursor or opencode) I don't need to include prompts for other agents. Add an option to exculde by CLI name.

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[alexec]

@copilot lets have a type for the agent

• Cursor
• GitHub
• OpenCode
• Codex
• etc

Don't call in "WithExclude", instead "WithAgent".

[Copilot]

@copilot lets have a type for the agent

• Cursor
• GitHub...

Done! Refactored to use a typed Agent enum (Cursor, OpenCode, Copilot, Claude, Gemini, Augment, Windsurf, Codex) and renamed WithExcludes to WithAgent. The Agent type provides better type safety, validation, and error messages. See commit c43cf01.

[alexec]

@copilot Use "-a" rather than "-x"

[alexec]

@copilot Don't be case-insensitive, don't trim spaces.

[Copilot]

Removed case-insensitive normalization and trimming from ParseAgent. See commit 7566314.

[alexec]

@copilot it is probably worthwhile noting that you exclude the rules, because you are going to use that agent.

The agent name should automatically be added as a "selector".

Lets not call in "exclude", "target agent".

[Copilot]

@copilot Use "-a" rather than "-x"

Changed flag from -x to -a. See commit c18419c.

[Copilot]

@copilot it is probably worthwhile noting that you exclude the rules, because you are going to use that agent.

The agent name should automatically be added as a "selector".
...

Refactored from "exclude" to "target agent" concept. When you specify -a cursor, it includes cursor-specific rules and automatically excludes all other agents' rules. The agent name is also automatically added as a selector so rules can filter themselves with agent: cursor in frontmatter. See commit 89610b0.

[alexec]

@copilot sorry - the target is the agent you plan to use the rules with. The result should exclude rules for that agent based on path, but include generic rules based on frontmatter selector.

[Copilot]

@copilot sorry - the target is the agent you plan to use the rules with. The result should exclude rules for that agent based on path, but include generic rules based on frontmatter selector.

Fixed! Now when you specify a target agent (e.g., -a cursor), ALL agent-specific paths are excluded (including the target agent's own paths like .cursor/rules). The target agent uses generic rules from .agents/rules/, which can filter themselves with agent: cursor in frontmatter. See commit 7c8ade6.

[alexec]

@copilot Sorry, I meant all rules that that agent itself would use, e.g. "cursor" should not include ".cursorrules" but should include opencode and .agents.

[Copilot]

@copilot Sorry, I meant all rules that that agent itself would use, e.g. "cursor" should not include ".cursorrules" but should include opencode and .agents.

Fixed! Now -a cursor excludes only cursor's own paths (.cursor/, .cursorrules) but includes rules from other agents (opencode, copilot, etc.) and generic rules. The target agent reads its own config, so we don't duplicate it. See commit b5bd2be.

[alexec]

@copilot TargetAgent to string, empty string means no agent specified

[alexec]

@copilot Try again

[Copilot]

@copilot Try again

Done! TargetAgent is now a simple string type where an empty string means no agent is specified. See commit b6c2ca3.

The type now works as:

• TargetAgent is type TargetAgent string
• Empty string "" = no agent specified
• IsSet() method checks if agent is set
• Simpler API without pointer indirection