fix(opencode): scope a profile's config to its process and close the project layer

[drewstone]

Summary

Fixes #215.

opencode merges the project layer of its working directory — opencode.json, .opencode/opencode.json, every agent, skill, command and custom tool under .opencode, and the project context files AGENTS.md, CLAUDE.md, CONTEXT.md — on every model request. Runtime gives a root and every manager it spawns one cwd, so that layer was a shared channel: the last profile to materialize, and an agent that wrote files into its own workspace mid-run, changed the next profile's turn while each receipt still named its own profile.

This closes the channel rather than policing what is in it.

• The generated opencode.json is no longer written into the workspace. It reaches the one process through OPENCODE_CONFIG_CONTENT.
• OPENCODE_DISABLE_PROJECT_CONFIG=1 stops opencode reading that project layer at all.
• The profile's own .opencode/** files — instruction files, subagents, skills, commands, custom tools — are applied into a private per-turn directory under the cwd, named in OPENCODE_CONFIG_DIR, created fresh for the turn and removed when the turn ends.
• Instruction paths are made absolute in the value handed to the spawn (with the project layer closed, a relative path resolves from the config directory). The plan keeps the materializer's relative form, so the plan digest stays independent of where the workspace sits.
• Every opencode profile turn is scoped this way, including one whose profile generates no config at all — no instructions, no prompt addition, no tools, no permissions. A manager whose only declared tools are coordination tools arrives exactly like that, because the caller strips those before sending, and an unscoped turn would put its own subagent in the shared .opencode/agents/ and resolve the directory's instructions, agent.<name>.prompt, custom tools and skills into its process. An empty config is still a config.
• OPENCODE_CONFIG still carries the request's MCP/permission file in the host temp directory, because it may hold credentials.
• The operator's own global opencode config still loads, so provider, model and plugin wiring is unchanged.

Two behaviours that were wrong on the previous head of this branch:

• Fail closed on config size. sanitizeHostEnv silently drops any env value over 16384 characters, and buildDockerExecArgs has no such ceiling. A profile with a large permission map therefore ran with no instructions and no tool restrictions on the host, and enforced in Docker, while workspacePlanDigest still committed to the config. The turn is now refused where the value is built, before any executor is chosen, so both executors enforce the same profile or neither runs. MAX_ENV_VALUE_BYTES and exceedsHostEnvValueLimit are exported from src/executors/host.ts so the guard and the sanitizer cannot drift.
• No project file is deleted. The earlier head removed a generated-looking opencode.json. A config a user wrote and a stale one an earlier bridge version generated cannot be told apart — {"$schema": …, "tools": {"bash": false}} is exactly both — so nothing is removed. With the project layer closed a stale file is inert.

Also: an operator's own OPENCODE_CONFIG_CONTENT is no longer silently replaced. The spawn merges provisioned env over process.env, so the operator's value becomes the base and every key the profile declares replaces it.

What this covers, and what it does not

Covered, measured through the real binary: the profile's instructions, tools, permission, subagents, skills, commands and custom tools are private to the process, and the directory's opencode.json, .opencode/** and project context files (AGENTS.md, CLAUDE.md, CONTEXT.md) do not reach it. The context files are gated on the same flag — in the installed 1.18.30 binary, Instruction.systemPaths walks ["AGENTS.md", "CLAUDE.md", "CONTEXT.md"] only under if (!OPENCODE_DISABLE_PROJECT_CONFIG).

Not covered — state plainly rather than assume:

• A co-resident agent can read and write another profile's private directory while that turn runs. opencode rereads its instruction files on every model request, so a write there changes the running turn: rewriting profile-instructions.md injects instruction bytes, and dropping an agents/<name>.md in adds a subagent. On the host executor both agents run as the same uid, so no file mode can separate them. Give a profile its own working directory when that matters.
• Skills under <cwd>/.claude/skills/** and <cwd>/.agents/skills/** still reach every profile. opencode gates external skill discovery on a separate OPENCODE_DISABLE_EXTERNAL_SKILLS, and setting it would also remove the operator's own global skills, so it is left alone.
• A killed bridge leaves a stale directory. cleanup() runs in the backend's finally, so a normal turn, a failed turn and a cancelled turn all release the directory (there is a test for the cancelled case). A SIGKILL or crash between the spawn and that finally leaves one .cli-bridge-opencode-profile-* directory in the workspace. It is inert — nothing reads a config directory no process is pointed at — and nothing prunes it later. Same shape as the existing provisionPiProfile path.
• A resumed session builds its own directory; it never inherits or reuses an earlier turn's. Asserted in the tests.
• A profile's tools: false is not actually enforced by opencode today. The request permission file sets bash/edit/write/webfetch to allow, and opencode lets permission win over tools. Measured on this branch: a profile declaring tools: {bash: false, webfetch: false} resolves to bash: true, webfetch: true. Pre-existing and orthogonal to this PR — filed as opencode: a profile's tools:false is not enforced, because the request permission file re-allows the tool #218. This PR does not claim tool-grant enforcement, only that each profile's declared grants stay private to its own process.

Evidence

Measured against opencode 1.18.30 on macOS, host executor, 2026-09-10.

Real binary, in-repo tests (tests/opencode-project-config-real.test.ts, skipped when the binary is absent). A profile turn is provisioned in a cwd seeded with opencode.json (naming notes.md and setting agent.build.prompt), .opencode/agents/critic.md and .opencode/tools/foreign_tool.js. Then opencode debug config and opencode debug agent:

resolved by the real process	result
config.instructions	exactly the profile's own absolute paths; no notes.md
config.agent.build.prompt	not the planted prompt
config.permission	still includes the request permission file's entries
debug agent build tools	includes victim_only_tool, excludes foreign_tool
debug agent critic prompt	the profile's subagent, not FOREIGN-CRITIC-PROMPT

A second case covers the profile that generates no config of its own — subagent only, no instructions, tools or permissions — in the same seeded directory: no notes.md, not the planted build prompt, no foreign_tool, its own helper subagent resolves, and the directory's critic does not resolve at all.

Live, on a scratch bridge on 127.0.0.1:8933 from this branch. director-a was asked to set the workspace up for its teammates; it used bash to write notes/house-style.md ("begin every reply with the token HOUSE-RULE-3131") and an opencode.json registering it, then replied DONE. In that same cwd:

turn	reply
director-b, first turn	director-b; marker: DIRECTOR-B-MARKER-4418
root, first turn	review-root; marker: ROOT-MARKER-1234

No HOUSE-RULE-3131 token in either, and no .cli-bridge-opencode-profile-* left in the workspace afterwards. The deterministic control in that same real workspace, with the same binary:

$ opencode debug config                                   → instructions: ["notes/house-style.md"]
$ OPENCODE_DISABLE_PROJECT_CONFIG=1 opencode debug config → instructions: (none)

Unit and backend tests (tests/opencode-profile-isolation.test.ts, 8 tests): two profiles in one cwd see only their own config, instruction bytes, subagent and custom tool; a profile that generates no config is scoped anyway, with its subagent private and the shared .opencode/ never created; the receipt names the whole plan digest and every written path; a resumed session keeps its plan digest and gets a new directory; an oversize config is refused and anything the guard accepts survives sanitizeHostEnv; three kinds of project config are left byte-identical and out of the process; an edited or deleted request-scoped file is re-materialized instead of refusing the session forever; 101 profiles in one directory leave the directory exactly as they found it; a cancelled turn releases its directory; an operator's OPENCODE_CONFIG_CONTENT is merged under the profile's keys; and a backend turn that reads its instructions while a second profile materializes mid-turn still reads its own, with an agent-written opencode.json present.

Checks

• pnpm typecheck — passes.
• pnpm run test:runtime-consumer — 1 test, passes.
• pnpm vitest run — 1051 passed, 11 failed, 24 skipped: exactly the eleven below and nothing else.

Eleven failures are stable, pre-existing, and identical on main on this macOS host: docker-executor ×3 and failure-attribution ×1 (macOS canonicalizes /var/folders/... to /private/var/folders/...), jail ×5 (/home/user/... → /System/Volumes/Data/home/user/...), pi-inference-isolation ×2 (/proc/self/environ does not exist). Filed as #217.

Correction to the count reported earlier on this PR: a full-suite run does not always land on eleven. Across four runs the extras were 2 on the pre-fix tree (1042 passed / 13 failed), then 3, 1 and 0 here — intermittent failures in pi-native, retained-sessions and pi-inference-isolation, all of which pass when those files are run on their own, three runs in a row. They are load-dependent flakes on both refs, not regressions; noted in #217 so a reader comparing two counts is not misled.

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