fix(github): explain empty-diff apply reconciliation

[aparajon]

Why

When a PR no longer contains managed schema files after an apply has started, SchemaBot should fail closed with clear reconciliation guidance instead of falling through to broad repository discovery or implying the PR is clean.

What

• Add empty-diff reconciliation handling for plan/apply/apply-confirm PR commands
• Render distinct guidance for in-progress vs completed apply-owned state
• Add preview scenarios and update the generated template snapshot

Risk Assessment

Medium — this changes GitHub PR-command behavior for a safety-gate edge case, but only when the current PR has no managed schema files and stored apply-owned state exists.

Generated with Amp

[Copilot]

Pull request overview

Adds explicit “empty diff” reconciliation behavior for SchemaBot PR commands so that when a schema apply has started (or completed) but the current PR no longer contains managed schema files, SchemaBot fails closed with actionable guidance rather than falling back to broad repository discovery.

Changes:

• Introduces reconciliation templates for “no managed schema changes” and “reconciliation required” (in-progress vs completed apply).
• Adds a webhook guard (handleNoManagedSchemaChangesForCommand) used by plan, apply, and apply-confirm to detect empty-diff + apply-owned state and post guidance.
• Extends preview scenarios/templates and adds E2E/unit tests for the new empty-diff behaviors (plan/apply covered).

Reviewed changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
TEMPLATES.md	Adds rendered template snapshots for no-managed and reconciliation-required scenarios.
pkg/webhook/webhook_e2e_test.go	Adds E2E coverage for empty-diff reconciliation behavior (plan/apply).
pkg/webhook/templates/reconciliation.go	Implements new comment renderers for no-managed changes and reconciliation-required guidance.
pkg/webhook/templates/reconciliation_test.go	Unit tests for the reconciliation templates.
pkg/webhook/templates/preview.go	Adds preview helpers for the new reconciliation comment scenarios.
pkg/webhook/schema_reconciliation.go	Adds the empty-diff guard + stored-state lookup to decide between “no managed changes” vs “reconcile”.
pkg/webhook/schema_reconciliation_test.go	Unit tests for PR-file detection and reconciliation item derivation.
pkg/webhook/plan.go	Runs the empty-diff reconciliation guard before schema discovery for plan.
pkg/webhook/apply_handlers.go	Runs the empty-diff reconciliation guard before schema discovery for apply and apply-confirm.
pkg/webhook/check_runs.go	Updates the user-facing block message for schema-removed-after-apply state.
pkg/cmd/internal/templates/preview.go	Adds new preview type constants for the reconciliation scenarios.
pkg/cmd/internal/templates/preview_dispatch.go	Dispatches the new preview types to the webhook template previews.
pkg/cmd/internal/templates/preview_comment.go	Includes the new previews in “all comment previews” output.
pkg/cmd/commands/preview.go	Wires the new preview types into CLI help and routing.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.