fix(installer): opencode .jsonc + AGENTS.md (0.7.8) (#163)

* release: 0.7.7 (multi-agent installer — Cursor, Codex, opencode)

* fix(installer): opencode .jsonc + AGENTS.md (0.7.8)

v0.7.7 wrote ~/.config/opencode/opencode.json, but opencode reads
opencode.jsonc by default — so the codegraph MCP entry never appeared
in any opencode session. Also installs AGENTS.md so opencode's model
reaches for codegraph_* tools instead of native Grep.

- Prefer existing .jsonc, fall back to .json, default new installs
  to .jsonc.
- Surgical edits via jsonc-parser preserve user comments and
  formatting across install / re-install / uninstall round-trips.
- Install AGENTS.md (global ~/.config/opencode/AGENTS.md, local
  ./AGENTS.md) with the shared INSTRUCTIONS_TEMPLATE — same
  marker-delimited approach Codex uses.
- +9 opencode-specific tests covering filename precedence, comment
  preservation, AGENTS.md install + sibling-content preservation,
  uninstall reverses both files.

575/575 tests pass. Hand-verified end-to-end: opencode session calls
codegraph_node + codegraph_callers for a structural query, zero Grep
calls.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* docs: overhaul CLAUDE.md and add scripts/release.sh + Cursor rules file

Replaces the old Claude-only CLAUDE.md with a comprehensive guide covering
the full project architecture, multi-agent installer, test conventions,
NodeKind/EdgeKind reference, and release workflow. Key additions:

- Documents the layered pipeline, all module paths, and the multi-target
  installer (targets/, registry.ts, AgentTarget interface).
- Adds the Cursor `--path` quirk and the "update all three surfaces" rule
  when changing MCP tool guidance.
- Documents `npm run eval`, `test:eval`, and the full set of build/test
  commands including single-file patterns.
- `scripts/release.sh` — idempotent bash script that tags the current
  commit, pushes the tag, and creates a GitHub Release whose notes are
  extracted from the matching `## [X.Y.Z]` block in CHANGELOG.md. Safe
  to re-run after partial failure.
- `.cursor/rules/codegraph.mdc` — Cursor-specific agent instructions
  (tool decision table, rules of thumb, index-lag warning) written by
  the installer and kept in sync with server-instructions.ts and
  instructions-template.ts.

---------

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.cursor/rules/codegraph.mdc

@@ -0,0 +1,37 @@
+---
+description: CodeGraph MCP usage guide — when to use which tool
+alwaysApply: true
+---
+<!-- CODEGRAPH_START -->
+## CodeGraph
+
+This project has a CodeGraph MCP server (`codegraph_*` tools) configured. CodeGraph is a tree-sitter-parsed knowledge graph of every symbol, edge, and file. Reads are sub-millisecond and return structural information grep cannot.
+
+### When to prefer codegraph over native search
+
+Use codegraph for **structural** questions — what calls what, what would break, where is X defined, what is X's signature. Use native grep/read only for **literal text** queries (string contents, comments, log messages) or after you already have a specific file open.
+
+| Question | Tool |
+|---|---|
+| "Where is X defined?" / "Find symbol named X" | `codegraph_search` |
+| "What calls function Y?" | `codegraph_callers` |
+| "What does Y call?" | `codegraph_callees` |
+| "What would break if I changed Z?" | `codegraph_impact` |
+| "Show me Y's signature / source / docstring" | `codegraph_node` |
+| "Give me focused context for a task/area" | `codegraph_context` |
+| "Survey an unfamiliar module/topic" | `codegraph_explore` |
+| "What files exist under path/" | `codegraph_files` |
+| "Is the index healthy?" | `codegraph_status` |
+
+### Rules of thumb
+
+- **Trust codegraph results.** They come from a full AST parse. Do NOT re-verify them with grep — that's slower, less accurate, and wastes context.
+- **Don't grep first** when looking up a symbol by name. `codegraph_search` is faster and returns kind + location + signature in one call.
+- **Don't chain `codegraph_search` + `codegraph_node`** when you just want context — `codegraph_context` is one call.
+- **`codegraph_explore` is the heavy hitter** for unfamiliar areas — it returns full source from all relevant files in one call, but is token-heavy. If your harness supports parallel subagents (e.g., Claude Code's Task tool), spawn one for explore-class questions to keep main session context clean.
+- **Index lag**: the file watcher debounces ~500ms behind writes; don't re-query immediately after editing a file in the same turn.
+
+### If `.codegraph/` doesn't exist
+
+The MCP server returns "not initialized." Ask the user: *"I notice this project doesn't have CodeGraph initialized. Want me to run `codegraph init -i` to build the index?"*
+<!-- CODEGRAPH_END -->