Extract core functionality into embeddable context package with visitor pattern

[Copilot]

Extracted the context assembly logic from the CLI into a standalone context package library that can be embedded in other Go applications.

Changes

• New context package with public API:

  • Config - configuration for context assembly with support for custom loggers and visitors
  • Assembler - assembles context from rules and task files via NewAssembler() and Assemble()
  • Frontmatter - type alias for YAML frontmatter metadata
  • Document - unified type representing both rules and tasks (Path, Content, Frontmatter, Tokens)
  • ParamMap, SelectorMap - parameter substitution and rule filtering
  • ParseMarkdownFile(), EstimateTokens() - utility functions
  • RuleVisitor interface - visitor pattern for customizing rule processing
  • DefaultRuleVisitor - default implementation using slog for logging

• Simplified main.go from 228 to 64 lines - now a thin CLI wrapper that prints the returned task document

• Comprehensive tests for all library components with example usage

• Visitor pattern implementation - enables custom processing of each selected rule

• Structured logging with slog - all progress messages use log/slog with configurable logger

• Task document return value - Assemble() returns (*Document, error) allowing callers to handle the task programmatically

API Changes

Before

assembler := context.NewAssembler(context.Config{
    TaskName: "fix-bug",
})
err := assembler.Assemble(ctx) // Prints task to stdout

After

assembler := context.NewAssembler(context.Config{
    TaskName: "fix-bug",
    Logger:   slog.Default(), // Optional custom logger
})
task, err := assembler.Assemble(ctx) // Returns task document
fmt.Println(task.Content) // Caller controls output

Custom Visitor Example

type CustomVisitor struct {}

func (v *CustomVisitor) VisitRule(ctx context.Context, doc *context.Document) error {
    // Custom processing logic
    fmt.Printf("Processing: %s (%d tokens)\n", doc.Path, doc.Tokens)
    return nil
}

assembler := context.NewAssembler(context.Config{
    TaskName: "my-task",
    Visitor:  &CustomVisitor{},
})

Integration with Main Branch

• Successfully rebased onto latest main branch
• Resolved merge conflicts in main.go, selector_map.go, selector_map_test.go
• Integrated new features from main:
  • Resume mode (-r flag) support
  • Task selection by frontmatter task_name field instead of filename
• All tests passing (including integration tests)
• Build successful

CLI behavior unchanged - all existing functionality preserved with backward-compatible improvements.

Original prompt

I want to make this into a library that can be embedded. Start by extracting the common code.

---

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[alexec]

@copilot I want the assemler to use the visitor pattern to visit each rule as it is selected.

[Copilot]

@copilot I want the assemler to use the visitor pattern to visit each rule as it is selected.

Implemented the visitor pattern for rule processing in commit 9edade7.

The changes include:

• RuleVisitor interface: Defines VisitRule(ctx, rule) method called for each selected rule
• Rule type: Contains Path, Content, Frontmatter, and Tokens for each rule
• DefaultRuleVisitor: Maintains existing behavior (writes to stdout, logs to stderr)
• Config.Visitor field: Optional visitor (defaults to DefaultRuleVisitor)

Example usage:

type CustomVisitor struct {}

func (v *CustomVisitor) VisitRule(ctx context.Context, rule *context.Rule) error {
    // Custom logic for each rule
    fmt.Printf("Processing: %s\n", rule.Path)
    return nil
}

assembler := context.NewAssembler(context.Config{
    TaskName: "my-task",
    Visitor:  &CustomVisitor{},
})

See examples/visitor/ for a complete example.

[alexec]

@copilot rebase this PR.

[alexec]

@copilot rebase this PR.

[Copilot]

@copilot rebase this PR.

I've completed the rebase onto main branch locally (commit b5ebe7a). The rebase resolved all conflicts and integrated the new features from main:

• Resume mode (-r flag) support added to context library
• Task selection by frontmatter task_name field instead of filename
• All tests passing including integration tests

However, I cannot force-push the rebased commits as the authentication method doesn't support it. The rebased branch is ready but needs to be force-pushed by someone with push access.

Alternatively, if you have admin access to the repository settings, you could enable "Allow force pushes" for me to complete the push.

[alexec]

@copilot changes requsted.

[alexec]

there's a type for this

[Copilot]

Fixed in f97f1b7. Introduced Frontmatter type as map[string]string alias instead of using the raw map type directly.

[alexec]

rather than print the task, return it

[Copilot]

Fixed in f97f1b7. Assemble() now returns (*Document, error) instead of printing the task to stdout. The caller can then handle the task document as needed.

[alexec]

don't log to stderr, use slog

[Copilot]

Fixed in f97f1b7. Replaced all fmt.Fprintf logging with slog. The assembler now uses a configurable *slog.Logger (defaults to one writing to configured Stderr) for all progress messages.

[alexec]

Both the task and the rules are the same structure. Introduce a type for both.

[Copilot]

Fixed in f97f1b7. Introduced Document type that represents both rules and tasks since they share the same structure (Path, Content, Frontmatter, Tokens). The RuleVisitor.VisitRule() method now receives *Document instead of *Rule.

[Copilot]

@copilot changes requsted.

All requested changes have been addressed in commit f97f1b7:

• Introduced Frontmatter and Document types
• Changed Assemble() to return the task document
• Replaced fmt logging with slog
• All tests passing