ADR-0175 - Single context gateway across harnesses

Context

The installed global policy governs conversation but leaves tool routing to unrelated vendor blocks. Codex and Claude Code therefore carry duplicated prose, imported RTK sidecars, and different lean-ctx rules. Kimi Code and ZCode receive neither context gateway. The result is drift, not choice.

RTK rewrites shell commands and does not intercept native reads or MCP tools [RTKHOOKS]. lean-ctx owns MCP reads, search, maps, shell dispatch, security, and recovery [LEANCTX]. Claude Code runs matching hooks in parallel, so independent shell rewriters cannot form a dependable pipeline [CLAUDEHOOKS].

Kimi Code defines a user-level AGENTS.md and user-level MCP configuration [KIMICODE]. ZCode defines ~/.zcode/AGENTS.md as its user-global instruction file [ZCODE].

Decision

1. Install one agent policy. policy/agent.md owns interaction economy, durable finding placement, and context-tool routing. Setup installs its exact bytes inside one neutral agent-policy block.
2. Use one gateway. When available, lean-ctx owns reads, search, code maps, and shell dispatch. RTK-supported commands run through ctx_shell with raw=true; lean-ctx does not recompress them. Unsupported commands use ordinary ctx_shell compression. Exact evidence bypasses filtering.
3. Keep a native fallback. Without ctx_* tools, agents use native tools and RTK for supported shell commands.
4. Forbid competing glue. Installed policy uses no RTK import, sidecar, symlink, or second shell rewrite hook. External binaries, MCP registration, and vendor hooks remain outside Suspec setup.
5. Cover current harnesses. Explicit setup targets are codex, claude-code, kimi-code, zcode, and opencode. Each maps to its ordinary native global instruction file.
6. Keep setup narrow. Setup writes only the named native instruction files. It does not install, configure, update, or remove RTK, lean-ctx, MCP servers, skills, or vendor runtime state.

Narrowed decisions

• ADR-0171: economy survives inside the broader agent policy.
• ADR-0172: explicit reversible setup survives; the payload and supported target set expand.
• ADR-0173: one native inline block survives; the economy-only marker retires.
• ADR-0174: fixed ordinary targets and fail-closed shadowing survive.

Consequences

• Every supported harness receives the same behavior bytes.
• One output has one compressor. Installed tools cooperate instead of racing.
• Suspec owns policy, not third-party installation.

Status

Accepted (2026-08-09). Narrows ADR-0171 through ADR-0174.