@sema-agent/core/dist/core/fs-write-gate-policy.js

Stateless, task-oriented AI agent core

import { canonicalizeTarget, lexicalViewOf, pathFamilyOf, writeTargetPath } from "../tools/fs/safety.js";
import { isWithin } from "./runner/session-rule-policy.js";
import { swallowedFenceRoot } from "./runner/advertised-writable-dirs.js";
import { declaredPathTargetOf, isProtectedWrite } from "./tool-registry.js";
import { pathTargetBaseOf } from "./effective-path-target.js";
const ask = (message) => ({ action: "ask", message, decisionReason: "rule" });
function absoluteRootOf(rootPath, envCwd) {
    return rootPath === undefined ? undefined : lexicalViewOf(rootPath, envCwd);
}
export const WRITE_EXEMPT_DIR_COVERS_ROOT_CODE = "config.write_exempt_dir_covers_root";
function assertExemptDirsDoNotCoverRoot(exemptDirs, rootLexical) {
    if (exemptDirs === undefined || rootLexical === undefined)
        return;
    for (const raw of exemptDirs) {
        if (!raw)
            continue;
        const dirLexical = lexicalViewOf(raw, rootLexical);
        const swallowed = swallowedFenceRoot(dirLexical, [rootLexical]);
        if (swallowed === undefined)
            continue;
        const e = new Error(`createFsWriteGatePolicy: exemptDirs entry "${raw}" resolves to ${dirLexical}, which covers this gate's root ${swallowed} — ` +
            `an exemption that holds the root auto-approves every write under it, which is the whole workspace, so the gate refuses to be built rather than run with write governance silently off. ` +
            `If that IS what this deployment wants, say it with the knob that means it: defaultWrite: "allow", an open write face, or a permission rule.`);
        e.code = WRITE_EXEMPT_DIR_COVERS_ROOT_CODE;
        e.detail = { exemptDir: raw, exemptDirResolved: dirLexical, root: swallowed };
        throw e;
    }
}
export function createFsWriteGatePolicy(opts) {
    const { env, rootPath, defaultWrite } = opts;
    const acceptDirs = opts.acceptDirs && opts.acceptDirs.length > 0 ? opts.acceptDirs : undefined;
    const exemptDirs = opts.exemptDirs && opts.exemptDirs.length > 0 ? opts.exemptDirs : undefined;
    const rootLexical = absoluteRootOf(rootPath, env.cwd);
    assertExemptDirsDoNotCoverRoot(exemptDirs, rootLexical);
    const guardedCapable = env.writeFileGuarded !== undefined;
    const advisory = guardedCapable
        ? ""
        : " (advisory adjudication: this environment provides no guarded write, so approval is judged before a separate, non-atomic write step)";
    return {
        async check(req, signal) {
            if (!isProtectedWrite(req))
                return { action: "allow" };
            if (opts.requireGuardedWrite === true && !guardedCapable) {
                return {
                    action: "deny",
                    message: `write tool "${req.toolName}" refused: this deployment requires guarded (atomic precondition-verified) writes (requireGuardedWrite), but the execution environment provides no writeFileGuarded capability — refusing rather than falling back to a non-atomic write`,
                    decisionReason: "rule",
                };
            }
            const declared = declaredPathTargetOf(req);
            const path = declared === undefined ? undefined : writeTargetPath(req, declared);
            if (path === undefined) {
                return ask(`write tool "${req.toolName}" requires approval: the call has no resolvable path target to confine${declared === undefined ? " (the tool declares no path target)" : ""}${advisory}`);
            }
            const canon = await canonicalizeTarget(env, path, signal, pathFamilyOf({ root: rootPath, cwd: req.cwd ?? env.cwd }), pathTargetBaseOf(declared, { root: rootPath, cwd: req.cwd }));
            if (!canon.ok) {
                return ask(`write to "${path}" requires approval: its real target could not be resolved (${canon.message})${advisory}`);
            }
            for (const root of req.advertisedWritableRoots ?? []) {
                if (isWithin(root, canon.key))
                    return { action: "allow" };
            }
            let fenceRootsCanonical;
            let refusedDomain;
            for (const [dirs, structural] of [
                [exemptDirs, true],
                [acceptDirs, false],
            ]) {
                if (!dirs)
                    continue;
                for (const raw of dirs) {
                    const dir = await canonicalizeTarget(env, raw, signal, pathFamilyOf({ root: rootPath ?? env.cwd }), rootPath);
                    if (!dir.ok)
                        continue;
                    if (structural) {
                        if (fenceRootsCanonical === undefined) {
                            const r = rootPath === undefined ? undefined : await canonicalizeTarget(env, rootPath, signal, pathFamilyOf({ root: rootPath }), undefined);
                            fenceRootsCanonical = r === undefined ? [] : r.ok ? [r.key] : "unresolved";
                        }
                        if (fenceRootsCanonical === "unresolved") {
                            refusedDomain ??= `"${raw}" (this task's root ${rootPath} could not be resolved, so a structural domain that may cover it grants nothing)`;
                            continue;
                        }
                        const swallowed = swallowedFenceRoot(dir.key, fenceRootsCanonical);
                        if (swallowed !== undefined) {
                            refusedDomain ??= `"${raw}" (resolves to ${dir.key}, which contains this task's root ${swallowed})`;
                            continue;
                        }
                    }
                    if (isWithin(dir.key, canon.key))
                        return { action: "allow" };
                }
            }
            if (opts.isExempt) {
                let exempt = false;
                try {
                    exempt = (await opts.isExempt(req.toolName, canon.key, req.face !== undefined ? { capabilityId: req.face.capabilityId, contractId: req.face.contractId, shapeDigest: req.face.shapeDigest } : undefined)) === true;
                }
                catch {
                    exempt = false;
                }
                if (exempt) {
                    return {
                        action: "allow",
                        message: `write to "${path}" allowed by session exemption (previously approved for this session)`,
                        decisionReason: "rule",
                    };
                }
            }
            if (defaultWrite === "allow")
                return { action: "allow" };
            const note = refusedDomain === undefined ? undefined : ` — note: the configured write domain ${refusedDomain} was not honored; a domain that holds the root would exempt every write under it`;
            if (opts.defaultAsk !== undefined)
                return opts.defaultAsk(path, note);
            return ask(`approve write to "${path}"?${advisory}${note ?? ""}`);
        },
    };
}