docs: update meta files for Rust-side CLAUDE* env var stripping

- .claude/CLAUDE.md: document dual-layer env var stripping (Rust + JS)
- docs/progress.md: add session entry for Rust-side stripping
- docs/task_plan.md: add CLAUDE* env var leak to errors table
- CHANGELOG.md: add fix entry under Unreleased
- .gitignore: exclude debug/, plugins/, projects/ (Claude Code working dirs)

docs/task_plan.md

@@ -188,4 +188,5 @@ See [phases.md](phases.md) for the full phased implementation plan.
 |---|---|---|---|
 | Blank screen, "rune_outside_svelte" runtime error | Store files used `.ts` extension but contain Svelte 5 `$state`/`$derived` runes. Runes only work in `.svelte` and `.svelte.ts` files. Compiler silently passes but fails at runtime. | Renamed stores to `.svelte.ts`, updated all import paths to use `.svelte` suffix | 2026-03-06 |
 | Agent sessions produce no output (silent hang) | Claude CLI v2.1.69 hangs when spawned via child_process.spawn() with piped stdio. Known bug: github.com/anthropics/claude-code/issues/6775 | Migrated sidecar from raw CLI spawning to `@anthropic-ai/claude-agent-sdk` query() function. SDK handles subprocess management internally. | 2026-03-06 |
+| CLAUDE* env vars leak to sidecar | When BTerminal launched from Claude Code terminal, CLAUDE* env vars trigger nesting detection in sidecar | Dual-layer stripping: Rust SidecarManager uses env_clear()+envs(clean_env) before spawn (primary), JS runner strips via SDK env option (defense-in-depth) | 2026-03-07 |
 | Running agents killed on pane remount | AgentPane.svelte onDestroy called stopAgent() on component unmount, including layout changes and remounts — not just explicit close. | Removed onDestroy from AgentPane. Moved stop-on-close to TilingGrid onClose handler which only fires on explicit user action. | 2026-03-06 |