chore: add changeset for 1.0.0 release (Fission-AI#578)

* Add changeset for v0.24.0 features

* Replace changeset with 1.0.0 release notes

Update from minor to major version bump. Rewrite release notes to
properly capture the OPSX workflow changes:

- Dynamic instructions based on artifact state
- Semantic spec syncing with ADDED/MODIFIED/REMOVED parsing
- Step-through artifacts with /opsx:continue
- Skills support alongside tool commands
- Breaking: old /openspec:* commands removed

* Rewrite 1.0.0 changeset with comprehensive release notes

Based on deep research into old vs new workflow:

Old workflow:
- 3 phase-locked commands (proposal → apply → archive)
- 8+ config files scattered at project root
- Static prompts, same instructions every time
- Text-based spec merging

New OPSX workflow:
- 10 action-based commands (do any action anytime)
- Dynamic instructions (context + rules + template layers)
- Artifact graph with dependency awareness
- Semantic spec syncing (ADDED/MODIFIED/REMOVED/RENAMED)
- Agent Skills standard for cross-editor compatibility
- 21 AI tools supported
- Onboarding skill for guided first experience

Author: TabishB

.changeset/opsx-1.0.md

@@ -0,0 +1,83 @@
+---
+"@fission-ai/openspec": major
+---
+
+## OpenSpec 1.0 — The OPSX Release
+
+The workflow has been rebuilt from the ground up. OPSX replaces the old phase-locked `/openspec:*` commands with an action-based system where AI understands what artifacts exist, what's ready to create, and what each action unlocks.
+
+### Breaking Changes
+
+- **Old commands removed** — `/openspec:proposal`, `/openspec:apply`, and `/openspec:archive` no longer exist
+- **Config files removed** — Tool-specific instruction files (`CLAUDE.md`, `.cursorrules`, `AGENTS.md`, `project.md`) are no longer generated
+- **Migration** — Run `openspec init` to upgrade. Legacy artifacts are detected and cleaned up with confirmation.
+
+### From Static Prompts to Dynamic Instructions
+
+**Before:** AI received the same static instructions every time, regardless of project state.
+
+**Now:** Instructions are dynamically assembled from three layers:
+1. **Context** — Project background from `config.yaml` (tech stack, conventions)
+2. **Rules** — Artifact-specific constraints (e.g., "propose spike tasks for unknowns")
+3. **Template** — The actual structure for the output file
+
+AI queries the CLI for real-time state: which artifacts exist, what's ready to create, what dependencies are satisfied, and what each action unlocks.
+
+### From Phase-Locked to Action-Based
+
+**Before:** Linear workflow — proposal → apply → archive. Couldn't easily go back or iterate.
+
+**Now:** Flexible actions on a change. Edit any artifact anytime. The artifact graph tracks state automatically.
+
+| Command | What it does |
+|---------|--------------|
+| `/opsx:explore` | Think through ideas before committing to a change |
+| `/opsx:new` | Start a new change |
+| `/opsx:continue` | Create one artifact at a time (step-through) |
+| `/opsx:ff` | Create all planning artifacts at once (fast-forward) |
+| `/opsx:apply` | Implement tasks |
+| `/opsx:verify` | Validate implementation matches artifacts |
+| `/opsx:sync` | Sync delta specs to main specs |
+| `/opsx:archive` | Archive completed change |
+| `/opsx:bulk-archive` | Archive multiple changes with conflict detection |
+| `/opsx:onboard` | Guided 15-minute walkthrough of complete workflow |
+
+### From Text Merging to Semantic Spec Syncing
+
+**Before:** Spec updates required manual merging or wholesale file replacement.
+
+**Now:** Delta specs use semantic markers that AI understands:
+- `## ADDED Requirements` — New requirements to add
+- `## MODIFIED Requirements` — Partial updates (add scenario without copying existing ones)
+- `## REMOVED Requirements` — Delete with reason and migration notes
+- `## RENAMED Requirements` — Rename preserving content
+
+Archive parses these at the requirement level, not brittle header matching.
+
+### From Scattered Files to Agent Skills
+
+**Before:** 8+ config files at project root + slash commands scattered across 21 tool-specific locations with different formats.
+
+**Now:** Single `.claude/skills/` directory with YAML-fronted markdown files. Auto-detected by Claude Code, Cursor, Windsurf. Cross-editor compatible.
+
+### New Features
+
+- **Onboarding skill** — `/opsx:onboard` walks new users through their first complete change with codebase-aware task suggestions and step-by-step narration (11 phases, ~15 minutes)
+
+- **21 AI tools supported** — Claude Code, Cursor, Windsurf, Continue, Gemini CLI, GitHub Copilot, Amazon Q, Cline, RooCode, Kilo Code, Auggie, CodeBuddy, Qoder, Qwen, CoStrict, Crush, Factory, OpenCode, Antigravity, iFlow, and Codex
+
+- **Interactive setup** — `openspec init` shows animated welcome screen and searchable multi-select for choosing tools. Pre-selects already-configured tools for easy refresh.
+
+- **Customizable schemas** — Define custom artifact workflows in `openspec/schemas/` without touching package code. Teams can share workflows via version control.
+
+### Bug Fixes
+
+- Fixed Claude Code YAML parsing failure when command names contained colons
+- Fixed task file parsing to handle trailing whitespace on checkbox lines
+- Fixed JSON instruction output to separate context/rules from template — AI was copying constraint blocks into artifact files
+
+### Documentation
+
+- New getting-started guide, CLI reference, concepts documentation
+- Removed misleading "edit mid-flight and continue" claims that weren't implemented
+- Added migration guide for upgrading from pre-OPSX versions