[plan-02] Spawn-Contract Templating — canonical ${CLAUDE_PLUGIN_ROOT} resolution across all hosts

Defect

The shell/command strings claude-mem templates for hooks and MCP subprocesses are not portable across hosts. On Windows the same root cause recurs in many surfaces: cmd.exe /c uvx … --with "pkg>=x" lets the shell eat >/< redirect operators, command:"sh" reappears where sh is not on PATH, chroma-mcp/mcp-search die instantly or time out, bash hooks pop visible cmd windows, where bun breaks under GBK/UTF-8 usernames, and the PATH prelude spawns a fresh login shell on every hook. All are one defect: there is no single, host-aware spawn contract that quotes arguments and resolves the interpreter/root canonically.

Children

• #2776 — Windows: chroma-mcp connection times out (-32000) despite healthy server + SDK 'poison' churn
• #2762 — Windows: cmd.exe /c uvx mangles >/< in --with version pins (one-line fix)
• #2757 — Windows: cmd.exe /c uvx --with "onnxruntime>=1.20" mangled by shell redirect operators
• #2716 — Regression (v13.4.0): chroma-mcp still dies instantly on Windows — #2701 cmd.exe quoting fix incomplete
• #2714 — Regression (v13.4.0): mcp-search fails on Windows -32000 — command:"sh" reappeared; sh not on PATH
• #2715 — Hook PATH prelude spawns a login shell on every hook (~0.27s × PostToolUse/UserPromptSubmit/Stop)
• #2755 — Windows + Claude Desktop: bash hooks spawn visible cmd windows on every event
• #2708 — where bun on Windows with Chinese (GBK/UTF-8) username
• #2706 — MCP keeps failing to connect (Windows)

Fix sequence

Design doc: plans/02-spawn-contract-templating.md. Centralize argv construction with host-aware quoting (no shell redirect exposure for uvx --with); resolve interpreter/root once; avoid login-shell-per-hook; suppress console windows on Windows GUI hosts; encode-safe path handling under non-UTF-8 locales.

Test matrix

Host	Shell	Required behavior
Windows	cmd.exe	uvx --with "pkg>=x" reaches uvx intact; no >/< mangling
Windows	PowerShell / Desktop	no visible cmd windows; chroma-mcp + mcp-search connect
Windows	GBK username	where bun / spawn resolves
all	all	no login shell spawned per hook

Out of scope

Hook IO channel/exit discipline (plan-01); worker process lifecycle (plan-03).