feat: add progressive enhancement example

[adnaan]

Summary

Add a complete todo app example demonstrating progressive enhancement - apps that work both with and without JavaScript enabled.

Features Demonstrated

• Dual-mode forms: Works via WebSocket (JS) or HTTP POST (no-JS)
• PRG pattern: Post-Redirect-Get prevents duplicate submissions on refresh
• Validation errors: Inline error display for both modes
• Flash messages: Success feedback after actions
• Auto-generated keys: No explicit data-key attribute needed

Files Added

File	Description
main.go	Todo app with add/toggle/delete actions
progressive-enhancement.tmpl	Template with dual-mode forms
progressive_enhancement_test.go	Comprehensive chromedp E2E tests
README.md	Documentation for the example

Test plan

• go test -v ./progressive-enhancement/... - all E2E tests pass
• Manual testing with JS enabled (WebSocket updates)
• Manual testing with JS disabled (HTTP form submissions)

Depends on: livetemplate/livetemplate#102

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR adds a comprehensive progressive enhancement example demonstrating how to build applications that work both with and without JavaScript enabled. The example implements a todo list application that uses WebSocket for real-time updates when JavaScript is available, and falls back to traditional HTTP form submissions with the POST-Redirect-GET pattern when JavaScript is disabled.

Changes:

• Adds a complete todo app with dual-mode forms supporting both WebSocket and HTTP POST
• Implements PRG pattern for non-JS clients to prevent duplicate submissions
• Includes comprehensive E2E tests using chromedp for both JS and no-JS scenarios

Reviewed changes

Copilot reviewed 5 out of 6 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
progressive-enhancement/main.go	Implements TodoController with Mount, Add, Toggle, and Delete actions
progressive-enhancement/progressive-enhancement.tmpl	HTML template with dual-mode forms and progressive enhancement support
progressive-enhancement/progressive_enhancement_test.go	Comprehensive E2E tests covering JS, no-JS, validation, and content negotiation
progressive-enhancement/README.md	Documentation explaining progressive enhancement concepts and usage
go.mod	Adds local replace directive for development
go.sum	Updates checksums for dependencies

---

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[Copilot]

The Delete action modifies the slice while iterating over it by using append with slice expressions. If the item to delete is not found, the function silently returns without any indication. Consider adding a flash message or error when the ID is not found, or at minimum ensure the flash message is only set when an item is actually deleted.

Suggested change

	for i := range state.Items {
	if state.Items[i].ID == id {
	state.Items = append(state.Items[:i], state.Items[i+1:]...)
	ctx.SetFlash("success", "Item deleted")
	break
	}
	}
	// Find index of the item to delete without modifying the slice during iteration.
	deleteIndex := -1
	for i, item := range state.Items {
	if item.ID == id {
	deleteIndex = i
	break
	}
	}
	if deleteIndex >= 0 {
	state.Items = append(state.Items[:deleteIndex], state.Items[deleteIndex+1:]...)
	ctx.SetFlash("success", "Item deleted")
	} else {
	ctx.SetFlash("error", "Item not found")
	}

[Copilot]

The Toggle action does not provide any feedback to the user when the toggle ID is not found. Consider adding a flash message for error cases or success confirmation, similar to the Delete action.

Suggested change

	id := ctx.GetString("id")
	for i := range state.Items {
	if state.Items[i].ID == id {
	state.Items[i].Completed = !state.Items[i].Completed
	break
	}
	}
	id := ctx.GetString("id")
	found := false
	for i := range state.Items {
	if state.Items[i].ID == id {
	state.Items[i].Completed = !state.Items[i].Completed
	found = true
	ctx.SetFlash("success", "Item updated")
	break
	}
	}
	if !found {
	ctx.SetFlash("error", "Item not found")
	}

[Copilot]

The Files section lists only three files but omits the test file. Consider adding progressive_enhancement_test.go to the list since it's part of the example and demonstrates E2E testing patterns.

Suggested change

	- `README.md` - This documentation
	- `README.md` - This documentation
	- `progressive_enhancement_test.go` - End-to-end tests for progressive enhancement behavior

[Copilot]

The cancel function is being reassigned on line 101, which shadows the previous cancel function from line 97. This means the first context created on line 97 will not be properly canceled. Consider using different variable names for the timeout context and its cancel function.

[Copilot]

The cancel function is being reassigned on line 54, which shadows the previous cancel function from line 50. This means the first context created on line 50 will not be properly canceled. Consider using different variable names for the timeout context and its cancel function.

Suggested change

	ctx, cancel = context.WithTimeout(ctx, 15*time.Second)
	defer cancel()
	ctx, timeoutCancel := context.WithTimeout(ctx, 15*time.Second)
	defer timeoutCancel()

[Copilot]

The replace directive points to a local worktree path that is specific to the development environment. This will break the build for anyone else trying to use this example. The replace directive should either be removed before merging (if the dependency is already published), or changed to point to a more portable location, or this file should be gitignored with a .example version checked in instead.

Suggested change

	// Use local livetemplate for progressive enhancement development
	replace github.com/livetemplate/livetemplate => ../../../livetemplate/.worktrees/progressive-enhancement