feat: add persona binding algorithm

docs/plan.md

@@ -1465,6 +1465,8 @@ Human required:
 - `artifact_timeout_exhausted`
 - `destructive_command_blocked`
 - `secret_access_blocked`
+- `backend_unavailable`
+- `no_eligible_persona`
 - `writeset_conflict`
 - `merge_conflict`
 - `objective_not_met`

packages/core/src/binding.test.ts

@@ -0,0 +1,429 @@
+import { describe, expect, it } from "vitest";
+import type { z } from "zod";
+
+import { type BindingOverride, bindTemplatePersonas } from "./binding.js";
+import type { BackendConfig } from "./config.js";
+import { DevflowError } from "./errors.js";
+import { hash } from "./hash.js";
+import { Persona } from "./persona.js";
+import { personaHash } from "./persona.js";
+import { Template } from "./template.js";
+
+const enabledBackends: BackendConfig[] = [
+  { id: "fake", enabled: true },
+  { id: "claude", enabled: true, binaryPath: process.execPath },
+  { id: "codex", enabled: true, binaryPath: process.execPath },
+];
+
+describe("binding algorithm", () => {
+  it("auto-selects deterministically by preferred backend, version, name, then hash", () => {
+    const result = bindTemplatePersonas({
+      runId: "run-1",
+      template: template({
+        roles: [
+          {
+            id: "implementer",
+            requiredCapabilities: ["code_edit"],
+            preferredBackends: ["claude", "fake"],
+          },
+        ],
+      }),
+      personas: [
+        persona({ name: "fake_v9", version: 9, backend: "fake", capabilities: ["code_edit"] }),
+        persona({ name: "claude_v1", version: 1, backend: "claude", capabilities: ["code_edit"] }),
+        persona({
+          name: "claude_v2_b",
+          version: 2,
+          backend: "claude",
+          capabilities: ["code_edit"],
+        }),
+        persona({
+          name: "claude_v2_a",
+          version: 2,
+          backend: "claude",
+          capabilities: ["code_edit"],
+        }),
+      ],
+      templateHash: "template-hash",
+      availableBackends: enabledBackends,
+    });
+
+    expect(result.bindings).toHaveLength(1);
+    expect(result.bindings[0]?.roleId).toBe("implementer");
+    expect(result.bindings[0]?.persona.name).toBe("claude_v2_a");
+  });
+
+  it("falls back to non-preferred personas only when preferred personas fail eligibility", () => {
+    const result = bindTemplatePersonas({
+      runId: "run-1",
+      template: template({
+        roles: [
+          {
+            id: "implementer",
+            requiredCapabilities: ["code_edit"],
+            preferredBackends: ["claude"],
+          },
+        ],
+      }),
+      personas: [
+        persona({ name: "claude_reader", backend: "claude", capabilities: ["code_review"] }),
+        persona({ name: "fake_implementer", backend: "fake", capabilities: ["code_edit"] }),
+      ],
+      templateHash: "template-hash",
+      availableBackends: enabledBackends,
+    });
+
+    expect(result.bindings[0]?.persona.name).toBe("fake_implementer");
+  });
+
+  it("does not fall back when preferred personas only fail allowed role checks", () => {
+    expect(() =>
+      bindTemplatePersonas({
+        runId: "run-1",
+        template: template({
+          roles: [
+            {
+              id: "implementer",
+              requiredCapabilities: ["code_edit"],
+              preferredBackends: ["claude"],
+            },
+          ],
+        }),
+        personas: [
+          persona({
+            name: "claude_restricted",
+            backend: "claude",
+            capabilities: ["code_edit"],
+            allowedRoles: ["reviewer"],
+          }),
+          persona({ name: "fake_implementer", backend: "fake", capabilities: ["code_edit"] }),
+        ],
+        templateHash: "template-hash",
+        availableBackends: enabledBackends,
+      }),
+    ).toThrow(/no_eligible_persona/);
+  });
+
+  it("fails instead of falling back when the selected preferred backend is unavailable", () => {
+    expect(() =>
+      bindTemplatePersonas({
+        runId: "run-1",
+        template: template({
+          roles: [
+            {
+              id: "implementer",
+              requiredCapabilities: ["code_edit"],
+              preferredBackends: ["codex"],
+            },
+          ],
+        }),
+        personas: [
+          persona({ name: "codex_implementer", backend: "codex", capabilities: ["code_edit"] }),
+          persona({ name: "fake_implementer", backend: "fake", capabilities: ["code_edit"] }),
+        ],
+        templateHash: "template-hash",
+        availableBackends: [{ id: "fake", enabled: true }],
+      }),
+    ).toThrow(/backend_unavailable/);
+  });
+
+  it("classifies binding failures as human-required DevflowError instances", () => {
+    try {
+      bindTemplatePersonas({
+        runId: "run-1",
+        template: template({
+          roles: [
+            {
+              id: "implementer",
+              requiredCapabilities: ["code_edit"],
+              preferredBackends: ["codex"],
+            },
+          ],
+        }),
+        personas: [persona({ name: "codex_implementer", backend: "codex" })],
+        templateHash: "template-hash",
+        availableBackends: [{ id: "codex", enabled: true }],
+      });
+    } catch (error) {
+      expect(error).toBeInstanceOf(DevflowError);
+      expect((error as DevflowError).class).toBe("human_required");
+      expect((error as DevflowError).code).toBe("backend_unavailable");
+      return;
+    }
+
+    throw new Error("expected binding to fail");
+  });
+
+  it("treats absolute backend paths as process-start resolved registry entries", () => {
+    const result = bindTemplatePersonas({
+      runId: "run-1",
+      template: template({
+        roles: [
+          {
+            id: "implementer",
+            requiredCapabilities: ["code_edit"],
+            preferredBackends: ["codex"],
+          },
+        ],
+      }),
+      personas: [persona({ name: "codex_implementer", backend: "codex" })],
+      templateHash: "template-hash",
+      availableBackends: [{ id: "codex", enabled: true, binaryPath: "/process/start/codex" }],
+    });
+
+    expect(result.bindings[0]?.backend).toBe("codex");
+  });
+
+  it("supports persona overrides and backend-constraining overrides", () => {
+    const result = bindTemplatePersonas({
+      runId: "run-1",
+      template: template({
+        roles: [{ id: "reviewer", requiredCapabilities: ["code_review"] }],
+      }),
+      personas: [
+        persona({ name: "fake_reviewer", backend: "fake", capabilities: ["code_review"] }),
+        persona({ name: "codex_reviewer", backend: "codex", capabilities: ["code_review"] }),
+      ],
+      overrides: { roles: { reviewer: { backend: "codex" } } },
+      templateHash: "template-hash",
+      availableBackends: enabledBackends,
+    });
+
+    expect(result.bindings[0]?.persona.name).toBe("codex_reviewer");
+
+    const swappedPersona = bindTemplatePersonas({
+      runId: "run-1",
+      template: template({
+        roles: [{ id: "reviewer", requiredCapabilities: ["code_review"] }],
+      }),
+      personas: [
+        persona({ name: "alpha_reviewer", backend: "fake", capabilities: ["code_review"] }),
+        persona({ name: "beta_reviewer", backend: "fake", capabilities: ["code_review"] }),
+      ],
+      overrides: { roles: { reviewer: { persona: "beta_reviewer" } } },
+      templateHash: "template-hash",
+      availableBackends: enabledBackends,
+    });
+
+    expect(swappedPersona.bindings[0]?.persona.name).toBe("beta_reviewer");
+  });
+
+  it("rejects typo override keys and normalizes explicit undefined override fields", () => {
+    const base = {
+      runId: "run-1",
+      template: template(),
+      personas: [persona({ name: "fake_implementer", backend: "fake" })],
+      templateHash: "template-hash",
+      availableBackends: enabledBackends,
+    };
+
+    expect(() =>
+      bindTemplatePersonas({
+        ...base,
+        overrides: {
+          roles: {
+            implementer: { backned: "codex" } as unknown as BindingOverride,
+          },
+        },
+      }),
+    ).toThrow(/Unrecognized key/);
+
+    expect(
+      bindTemplatePersonas({
+        ...base,
+        overrides: {
+          roles: {
+            implementer: {
+              persona: undefined,
+              backend: undefined,
+            } as unknown as BindingOverride,
+          },
+        },
+      }).bindings[0]?.persona.name,
+    ).toBe("fake_implementer");
+
+    expect(() =>
+      bindTemplatePersonas({
+        ...base,
+        overrides: {
+          roles: {
+            implmenter: { backend: "fake" },
+          },
+        },
+      }),
+    ).toThrow(/unknown override role/);
+  });
+
+  it("computes binding hashes from the locked hash subject", () => {
+    const override = { backend: "fake" as const };
+    const result = bindTemplatePersonas({
+      runId: "run-1",
+      template: template({
+        roles: [
+          {
+            id: "reviewer",
+            requiredCapabilities: ["code_review"],
+            count: 2,
+          },
+        ],
+      }),
+      personas: [
+        persona({ name: "fake_reviewer", backend: "fake", capabilities: ["code_review"] }),
+      ],
+      overrides: { roles: { "reviewer#1": override } },
+      templateHash: "template-hash",
+      availableBackends: enabledBackends,
+    });
+    const binding = result.bindings.find((candidate) => candidate.roleId === "reviewer#1");
+    const selectedPersonaHash = personaHash(binding?.persona);
+
+    expect(binding?.bindingHash).toBe(
+      hash({
+        runId: "run-1",
+        roleId: "reviewer#1",
+        templateHash: "template-hash",
+        personaHash: selectedPersonaHash,
+        backend: "fake",
+        override,
+      }),
+    );
+  });
+
+  it("expands counted roles and enforces backend diversity after overrides", () => {
+    const result = bindTemplatePersonas({
+      runId: "run-1",
+      template: template({
+        roles: [
+          {
+            id: "reviewer",
+            requiredCapabilities: ["code_review"],
+            count: 2,
+            diversity: { requireDifferentBackends: true },
+          },
+        ],
+      }),
+      personas: [
+        persona({ name: "fake_reviewer", backend: "fake", capabilities: ["code_review"] }),
+        persona({ name: "codex_reviewer", backend: "codex", capabilities: ["code_review"] }),
+      ],
+      templateHash: "template-hash",
+      availableBackends: enabledBackends,
+    });
+
+    expect(result.bindings.map((binding) => binding.roleId)).toEqual(["reviewer#0", "reviewer#1"]);
+    expect(new Set(result.bindings.map((binding) => binding.backend)).size).toBe(2);
+
+    const constrainedSecondInstance = bindTemplatePersonas({
+      runId: "run-1",
+      template: template({
+        roles: [
+          {
+            id: "reviewer",
+            requiredCapabilities: ["code_review"],
+            count: 2,
+            diversity: { requireDifferentBackends: true },
+          },
+        ],
+      }),
+      personas: [
+        persona({ name: "fake_reviewer", backend: "fake", capabilities: ["code_review"] }),
+        persona({ name: "codex_reviewer", backend: "codex", capabilities: ["code_review"] }),
+      ],
+      overrides: { roles: { "reviewer#1": { backend: "fake" } } },
+      templateHash: "template-hash",
+      availableBackends: enabledBackends,
+    });
+
+    expect(constrainedSecondInstance.bindings.map((binding) => binding.backend)).toEqual([
+      "codex",
+      "fake",
+    ]);
+  });
+
+  it("rejects unavailable backends, missing capabilities, role restrictions, and risk overflow", () => {
+    const base = {
+      runId: "run-1",
+      templateHash: "template-hash",
+      availableBackends: [{ id: "fake", enabled: true }] satisfies BackendConfig[],
+    };
+
+    expect(() =>
+      bindTemplatePersonas({
+        ...base,
+        template: template({ roles: [{ id: "implementer", requiredCapabilities: ["code_edit"] }] }),
+        personas: [persona({ name: "disabled", backend: "codex", capabilities: ["code_edit"] })],
+      }),
+    ).toThrow(/backend_unavailable/);
+
+    expect(() =>
+      bindTemplatePersonas({
+        ...base,
+        template: template({ roles: [{ id: "implementer", requiredCapabilities: ["code_edit"] }] }),
+        personas: [persona({ name: "reviewer", backend: "fake", capabilities: ["code_review"] })],
+      }),
+    ).toThrow(/no_eligible_persona/);
+
+    expect(() =>
+      bindTemplatePersonas({
+        ...base,
+        template: template({ roles: [{ id: "implementer", requiredCapabilities: ["code_edit"] }] }),
+        personas: [
+          persona({
+            name: "restricted",
+            backend: "fake",
+            capabilities: ["code_edit"],
+            allowedRoles: ["reviewer"],
+          }),
+        ],
+      }),
+    ).toThrow(/no_eligible_persona/);
+
+    expect(() =>
+      bindTemplatePersonas({
+        ...base,
+        template: template({
+          roles: [{ id: "implementer", requiredCapabilities: ["code_edit"] }],
+          phases: [{ key: "danger", title: "Danger", risk: "high", roles: ["implementer"] }],
+        }),
+        personas: [
+          persona({
+            name: "medium_only",
+            backend: "fake",
+            capabilities: ["code_edit"],
+            maxRiskLevel: "medium",
+          }),
+        ],
+      }),
+    ).toThrow(/no_eligible_persona/);
+  });
+});
+
+function template(input: Partial<z.input<typeof Template>> = {}): Template {
+  const roles = input.roles ?? [{ id: "implementer", requiredCapabilities: ["code_edit"] }];
+  const phases = input.phases ?? [
+    { key: "spec", title: "Spec", risk: "low", roles: [roles[0]?.id ?? "implementer"] },
+  ];
+
+  return Template.parse({
+    name: input.name ?? "development",
+    version: input.version ?? 1,
+    roles,
+    phases,
+    defaultGates: input.defaultGates ?? [],
+  });
+}
+
+function persona(
+  input: Partial<z.input<typeof Persona>> & Pick<z.input<typeof Persona>, "name">,
+): Persona {
+  return Persona.parse({
+    name: input.name,
+    version: input.version ?? 1,
+    backend: input.backend ?? "fake",
+    capabilities: input.capabilities ?? ["code_edit"],
+    maxRiskLevel: input.maxRiskLevel ?? "high",
+    promptConfig: input.promptConfig ?? {},
+    modelConfig: input.modelConfig ?? {},
+    ...(input.allowedRoles === undefined ? {} : { allowedRoles: input.allowedRoles }),
+  });
+}

packages/core/src/binding.ts

@@ -0,0 +1,384 @@
+import { isAbsolute } from "node:path";
+import { z } from "zod";
+
+import type { BackendConfig } from "./config.js";
+import { Backend } from "./enums.js";
+import { DevflowError } from "./errors.js";
+import { hash } from "./hash.js";
+import { type Persona, personaHash } from "./persona.js";
+import type { Template, TemplateRole } from "./template.js";
+
+const riskRank = { low: 0, medium: 1, high: 2 } as const;
+
+export const BindingOverride = z
+  .object({
+    persona: z.string().optional(),
+    backend: Backend.optional(),
+  })
+  .strict();
+
+export const BindingOverrides = z
+  .object({
+    roles: z.record(BindingOverride).default({}),
+  })
+  .strict();
+
+export type BindingOverride = z.infer<typeof BindingOverride>;
+export type BindingOverrides = z.infer<typeof BindingOverrides>;
+
+export interface BindTemplatePersonasInput {
+  runId: string;
+  template: Template;
+  personas: Persona[];
+  templateHash: string;
+  availableBackends: readonly BackendConfig[];
+  overrides?: Partial<BindingOverrides>;
+}
+
+export interface RoleBinding {
+  roleId: string;
+  templateRoleId: string;
+  persona: Persona;
+  personaHash: string;
+  backend: Backend;
+  bindingHash: string;
+}
+
+export interface BindingResult {
+  bindings: RoleBinding[];
+}
+
+export function bindTemplatePersonas(input: BindTemplatePersonasInput): BindingResult {
+  const overrides = BindingOverrides.parse(input.overrides ?? {});
+  assertOverrideRoleKeys(input.template, overrides);
+  const bindings: RoleBinding[] = [];
+
+  for (const role of input.template.roles) {
+    const assignments = selectRoleAssignments(input, role, overrides);
+
+    for (const assignment of assignments) {
+      const { roleId, override, candidate } = assignment;
+      const personaHashValue = personaHash(candidate);
+      bindings.push({
+        roleId,
+        templateRoleId: role.id,
+        persona: candidate,
+        personaHash: personaHashValue,
+        backend: candidate.backend,
+        bindingHash: hash({
+          runId: input.runId,
+          roleId,
+          templateHash: input.templateHash,
+          personaHash: personaHashValue,
+          backend: candidate.backend,
+          override,
+        }),
+      });
+    }
+  }
+
+  return { bindings };
+}
+
+interface RoleAssignment {
+  roleId: string;
+  override: BindingOverride;
+  candidate: Persona;
+}
+
+function selectRoleAssignments(
+  input: BindTemplatePersonasInput,
+  role: TemplateRole,
+  overrides: BindingOverrides,
+): RoleAssignment[] {
+  const instances = roleInstances(role).map((roleId) => ({
+    roleId,
+    override: normalizeOverride(overrides.roles[roleId] ?? overrides.roles[role.id]),
+  }));
+  const candidateLists = instances.map((instance) => ({
+    ...instance,
+    candidates: candidatesForRoleInstance(input, role, instance.override),
+  }));
+
+  for (const list of candidateLists) {
+    if (list.candidates.length === 0) {
+      throw noEligiblePersona(list.roleId);
+    }
+  }
+
+  const assignments = assignCandidates(
+    candidateLists,
+    role.diversity?.requireDifferentBackends === true,
+  );
+  if (assignments === undefined) {
+    throw noEligiblePersona(role.id, "diversity failed");
+  }
+
+  return instances.map((instance) => {
+    const candidate = assignments.get(instance.roleId);
+    if (candidate === undefined) {
+      throw noEligiblePersona(instance.roleId);
+    }
+
+    return { ...instance, candidate };
+  });
+}
+
+function roleInstances(role: TemplateRole): string[] {
+  if (role.count === 1) {
+    return [role.id];
+  }
+
+  return Array.from({ length: role.count }, (_, index) => `${role.id}#${index}`);
+}
+
+function assertOverrideRoleKeys(template: Template, overrides: BindingOverrides) {
+  const validRoleIds = new Set<string>();
+
+  for (const role of template.roles) {
+    validRoleIds.add(role.id);
+
+    if (role.count > 1) {
+      for (let index = 0; index < role.count; index += 1) {
+        validRoleIds.add(`${role.id}#${index}`);
+      }
+    }
+  }
+
+  for (const roleId of Object.keys(overrides.roles)) {
+    if (!validRoleIds.has(roleId)) {
+      throw noEligiblePersona(roleId, "unknown override role");
+    }
+  }
+}
+
+interface CandidateList {
+  roleId: string;
+  override?: BindingOverride | undefined;
+  candidates: Persona[];
+}
+
+function candidatesForRoleInstance(
+  input: BindTemplatePersonasInput,
+  role: TemplateRole,
+  override: BindingOverride | undefined,
+): Persona[] {
+  const normalizedOverride = normalizeOverride(override);
+  const candidates: Persona[] = [];
+  const sortedCandidates = sortCandidates(input.personas, role)
+    .filter((persona) =>
+      normalizedOverride.persona === undefined ? true : persona.name === normalizedOverride.persona,
+    )
+    .filter((persona) =>
+      normalizedOverride.backend === undefined
+        ? true
+        : persona.backend === normalizedOverride.backend,
+    );
+  const selectableCandidates = hasOverrideConstraint(normalizedOverride)
+    ? sortedCandidates
+    : applyPreferredFallbackRule(sortedCandidates, role, input.template);
+
+  for (const candidate of selectableCandidates) {
+    if (!isEligible(candidate, role, input.template)) {
+      continue;
+    }
+
+    if (!isBackendAvailable(candidate.backend, input.availableBackends)) {
+      if (candidates.length === 0) {
+        throw backendUnavailable(candidate.backend);
+      }
+
+      continue;
+    }
+
+    candidates.push(candidate);
+  }
+
+  return candidates;
+}
+
+function hasOverrideConstraint(override: BindingOverride) {
+  return override.persona !== undefined || override.backend !== undefined;
+}
+
+function applyPreferredFallbackRule(
+  candidates: Persona[],
+  role: TemplateRole,
+  template: Template,
+): Persona[] {
+  if (role.preferredBackends.length === 0) {
+    return candidates;
+  }
+
+  const preferredCandidates = candidates.filter((candidate) =>
+    role.preferredBackends.includes(candidate.backend),
+  );
+  if (preferredCandidates.length === 0) {
+    return candidates;
+  }
+
+  const allPreferredFailCapabilityOrRisk = preferredCandidates.every(
+    (candidate) => !capabilitiesCovered(candidate, role) || !riskCovered(candidate, role, template),
+  );
+
+  return allPreferredFailCapabilityOrRisk ? candidates : preferredCandidates;
+}
+
+function assignCandidates(
+  candidateLists: CandidateList[],
+  requireDifferentBackends: boolean,
+): Map<string, Persona> | undefined {
+  return assignCandidatesAt(candidateLists, requireDifferentBackends, 0, new Map(), new Set());
+}
+
+function assignCandidatesAt(
+  candidateLists: CandidateList[],
+  requireDifferentBackends: boolean,
+  index: number,
+  assignments: Map<string, Persona>,
+  selectedBackends: Set<Backend>,
+): Map<string, Persona> | undefined {
+  if (index >= candidateLists.length) {
+    return assignments;
+  }
+
+  const candidateList = candidateLists[index];
+  if (candidateList === undefined) {
+    return assignments;
+  }
+
+  for (const candidate of candidateList.candidates) {
+    if (requireDifferentBackends && selectedBackends.has(candidate.backend)) {
+      continue;
+    }
+
+    const nextAssignments = new Map(assignments);
+    const nextBackends = new Set(selectedBackends);
+    nextAssignments.set(candidateList.roleId, candidate);
+    nextBackends.add(candidate.backend);
+
+    const result = assignCandidatesAt(
+      candidateLists,
+      requireDifferentBackends,
+      index + 1,
+      nextAssignments,
+      nextBackends,
+    );
+    if (result !== undefined) {
+      return result;
+    }
+  }
+
+  return undefined;
+}
+
+function normalizeOverride(override: BindingOverride | undefined): BindingOverride {
+  const parsed = BindingOverride.parse(override ?? {});
+  const normalized: BindingOverride = {};
+
+  if (parsed.persona !== undefined) {
+    normalized.persona = parsed.persona;
+  }
+
+  if (parsed.backend !== undefined) {
+    normalized.backend = parsed.backend;
+  }
+
+  return normalized;
+}
+
+function sortCandidates(personas: Persona[], role: TemplateRole) {
+  return [...personas].sort((left, right) => {
+    const leftPreferredRank = preferredBackendRank(left.backend, role);
+    const rightPreferredRank = preferredBackendRank(right.backend, role);
+
+    return (
+      leftPreferredRank - rightPreferredRank ||
+      right.version - left.version ||
+      compareCodeUnits(left.name, right.name) ||
+      compareCodeUnits(personaHash(left), personaHash(right))
+    );
+  });
+}
+
+function preferredBackendRank(backend: Backend, role: TemplateRole) {
+  const rank = role.preferredBackends.indexOf(backend);
+  if (rank >= 0) {
+    return rank;
+  }
+
+  return role.preferredBackends.length;
+}
+
+function isEligible(persona: Persona, role: TemplateRole, template: Template) {
+  return (
+    roleAllowed(persona, role) &&
+    capabilitiesCovered(persona, role) &&
+    riskCovered(persona, role, template)
+  );
+}
+
+function roleAllowed(persona: Persona, role: TemplateRole) {
+  return persona.allowedRoles === undefined || persona.allowedRoles.includes(role.id);
+}
+
+function capabilitiesCovered(persona: Persona, role: TemplateRole) {
+  const capabilities = new Set(persona.capabilities);
+  return role.requiredCapabilities.every((capability) => capabilities.has(capability));
+}
+
+function riskCovered(persona: Persona, role: TemplateRole, template: Template) {
+  const phaseRisk = template.phases
+    .filter((phase) => phase.roles.includes(role.id))
+    .reduce<number>((maxRisk, phase) => Math.max(maxRisk, riskRank[phase.risk]), riskRank.low);
+
+  return phaseRisk <= riskRank[persona.maxRiskLevel];
+}
+
+function isBackendAvailable(backend: Backend, availableBackends: readonly BackendConfig[]) {
+  if (backend === "fake") {
+    return true;
+  }
+
+  return availableBackends.some(
+    (backendConfig) =>
+      backendConfig.id === backend &&
+      backendConfig.enabled &&
+      isResolvedBinaryPath(backendConfig.binaryPath),
+  );
+}
+
+function isResolvedBinaryPath(path: string | undefined) {
+  return typeof path === "string" && path.length > 0 && isAbsolute(path);
+}
+
+function backendUnavailable(backend: string) {
+  return new DevflowError(`human_required:backend_unavailable:${backend}`, {
+    class: "human_required",
+    code: "backend_unavailable",
+    recoveryHint: `Enable ${backend} and ensure its binary resolves at process start.`,
+  });
+}
+
+function noEligiblePersona(roleId: string, reason?: string) {
+  return new DevflowError(
+    `human_required:no_eligible_persona:${roleId}${reason === undefined ? "" : `:${reason}`}`,
+    {
+      class: "human_required",
+      code: "no_eligible_persona",
+      recoveryHint: `Add or override a persona eligible for role ${roleId}.`,
+    },
+  );
+}
+
+function compareCodeUnits(left: string, right: string) {
+  if (left < right) {
+    return -1;
+  }
+
+  if (left > right) {
+    return 1;
+  }
+
+  return 0;
+}

packages/core/src/config.test.ts

@@ -1,9 +1,10 @@
-import { mkdirSync, mkdtempSync, realpathSync, writeFileSync } from "node:fs";
+import { chmodSync, mkdirSync, mkdtempSync, realpathSync, writeFileSync } from "node:fs";
 import { tmpdir } from "node:os";
 import { join } from "node:path";
 import { describe, expect, it } from "vitest";
 
 import { loadConfigFromSources } from "./config.js";
+import { DevflowError } from "./errors.js";
 
 describe("config loader", () => {
   it("loads .env, .env.local, then process env in descending precedence", () => {
@@ -49,7 +50,100 @@ describe("config loader", () => {
     expect(config.backends).toContainEqual({ id: "fake", enabled: true });
   });
 
-  it("parses backend registration from DEVFLOW_BACKENDS_JSON", () => {
+  it("resolves backend binaries from PATH during config load", () => {
+    const root = mkdtempSync(join(tmpdir(), "devflow-config-"));
+    const workspace = join(root, "workspace");
+    const binDir = join(root, "bin");
+    const codexBin = join(binDir, "codex");
+    mkdirSync(workspace);
+    mkdirSync(binDir);
+    writeFileSync(codexBin, "#!/bin/sh\nexit 0\n");
+    chmodSync(codexBin, 0o755);
+
+    const config = loadConfigFromSources({
+      cwd: root,
+      env: {
+        DATABASE_URL: "postgres://devflow:devflow@localhost:5432/devflow",
+        WORKSPACE_ROOT: workspace,
+        LOG_LEVEL: "info",
+        PATH: binDir,
+        DEVFLOW_BACKENDS_JSON: JSON.stringify([{ id: "codex", enabled: true }]),
+      },
+    });
+
+    expect(config.backends).toEqual([
+      { id: "fake", enabled: true },
+      { id: "codex", enabled: true, binaryPath: realpathSync(codexBin) },
+    ]);
+  });
+
+  it("keeps enabled real backends unavailable when their binary cannot be resolved", () => {
+    const root = mkdtempSync(join(tmpdir(), "devflow-config-"));
+    const workspace = join(root, "workspace");
+    const emptyBin = join(root, "empty-bin");
+    mkdirSync(workspace);
+    mkdirSync(emptyBin);
+
+    const config = loadConfigFromSources({
+      cwd: root,
+      env: {
+        DATABASE_URL: "postgres://devflow:devflow@localhost:5432/devflow",
+        WORKSPACE_ROOT: workspace,
+        LOG_LEVEL: "info",
+        PATH: emptyBin,
+        DEVFLOW_BACKENDS_JSON: JSON.stringify([{ id: "codex", enabled: true }]),
+      },
+    });
+
+    expect(config.backends).toEqual([
+      { id: "fake", enabled: true },
+      { id: "codex", enabled: true },
+    ]);
+  });
+
+  it("requires LOG_LEVEL and classifies invalid config as fatal", () => {
+    const root = mkdtempSync(join(tmpdir(), "devflow-config-"));
+    const workspace = join(root, "workspace");
+    mkdirSync(workspace);
+
+    let caught: unknown;
+    try {
+      loadConfigFromSources({
+        cwd: root,
+        env: {
+          DATABASE_URL: "postgres://devflow:devflow@localhost:5432/devflow",
+          WORKSPACE_ROOT: workspace,
+        },
+      });
+    } catch (error) {
+      caught = error;
+    }
+
+    expect(caught).toBeInstanceOf(DevflowError);
+    expect((caught as DevflowError).class).toBe("fatal");
+    expect((caught as DevflowError).code).toBe("config_invalid");
+    expect((caught as DevflowError).cause).toBeDefined();
+  });
+
+  it("classifies malformed backend JSON as invalid config", () => {
+    const root = mkdtempSync(join(tmpdir(), "devflow-config-"));
+    const workspace = join(root, "workspace");
+    mkdirSync(workspace);
+
+    expect(() =>
+      loadConfigFromSources({
+        cwd: root,
+        env: {
+          DATABASE_URL: "postgres://devflow:devflow@localhost:5432/devflow",
+          WORKSPACE_ROOT: workspace,
+          LOG_LEVEL: "info",
+          DEVFLOW_BACKENDS_JSON: "{",
+        },
+      }),
+    ).toThrow(DevflowError);
+  });
+
+  it("freezes config and backend registrations", () => {
     const root = mkdtempSync(join(tmpdir(), "devflow-config-"));
     const workspace = join(root, "workspace");
     mkdirSync(workspace);
@@ -60,15 +154,14 @@ describe("config loader", () => {
         DATABASE_URL: "postgres://devflow:devflow@localhost:5432/devflow",
         WORKSPACE_ROOT: workspace,
         LOG_LEVEL: "info",
-        DEVFLOW_BACKENDS_JSON: JSON.stringify([
-          { id: "codex", enabled: true, binaryPath: "/usr/local/bin/codex" },
-        ]),
       },
     });
 
-    expect(config.backends).toEqual([
+    expect(Object.isFrozen(config)).toBe(true);
-      { id: "fake", enabled: true },
+    expect(Object.isFrozen(config.backends)).toBe(true);
-      { id: "codex", enabled: true, binaryPath: "/usr/local/bin/codex" },
+    expect(Object.isFrozen(config.backends[0])).toBe(true);
-    ]);
+    expect(() => {
+      (config.backends[0] as { enabled: boolean }).enabled = false;
+    }).toThrow(TypeError);
   });
 });

packages/core/src/config.ts

@@ -1,9 +1,10 @@
-import { existsSync, readFileSync, realpathSync } from "node:fs";
+import { constants, accessSync, existsSync, readFileSync, realpathSync, statSync } from "node:fs";
-import { resolve } from "node:path";
+import { delimiter, isAbsolute, resolve } from "node:path";
 import { parse } from "dotenv";
 import { z } from "zod";
 
 import { Backend } from "./enums.js";
+import { DevflowError } from "./errors.js";
 
 const LogLevel = z.enum(["trace", "debug", "info", "warn", "error"]);
 
@@ -13,32 +14,31 @@ export const BackendConfig = z.object({
   binaryPath: z.string().optional(),
 });
 
-export const ConfigSchema = z
+export type BackendConfig = z.infer<typeof BackendConfig>;
-  .object({
+
+const RawConfigSchema = z.object({
   DATABASE_URL: z.string().min(1),
   WORKSPACE_ROOT: z.string().min(1),
-    LOG_LEVEL: LogLevel.default("info"),
+  LOG_LEVEL: LogLevel,
   TEMPORAL_ADDRESS: z.string().optional(),
   MAX_CONCURRENT_RUNS: z.coerce.number().int().positive().default(4),
   backends: z.array(BackendConfig).default([{ id: "fake", enabled: true }]),
-  })
-  .transform((value) => {
-    const canonicalWorkspaceRoot = realpathSync(resolve(value.WORKSPACE_ROOT));
-    const hasFakeBackend = value.backends.some((backend) => backend.id === "fake");
-
-    return Object.freeze({
-      ...value,
-      WORKSPACE_ROOT: canonicalWorkspaceRoot,
-      backends: Object.freeze(
-        hasFakeBackend
-          ? value.backends
-          : [{ id: "fake" as const, enabled: true }, ...value.backends],
-      ),
-    });
 });
 
-export type BackendConfig = z.infer<typeof BackendConfig>;
+type RawConfig = z.infer<typeof RawConfigSchema>;
-export type Config = z.infer<typeof ConfigSchema>;
+
+export type Config = Omit<RawConfig, "WORKSPACE_ROOT" | "backends"> & {
+  readonly WORKSPACE_ROOT: string;
+  readonly backends: readonly BackendConfig[];
+};
+
+export const ConfigSchema = RawConfigSchema.transform(
+  (value): Config =>
+    finalizeConfig(value, {
+      cwd: process.cwd(),
+      pathEnv: process.env.PATH,
+    }),
+);
 
 export interface LoadConfigOptions {
   cwd?: string;
@@ -56,6 +56,7 @@ function readEnvFile(cwd: string, fileName: string): Record<string, string> {
 }
 
 export function loadConfigFromSources(options: LoadConfigOptions = {}): Config {
+  try {
     const cwd = options.cwd ?? process.cwd();
     const env = options.env ?? process.env;
     const raw = {
@@ -69,7 +70,17 @@ export function loadConfigFromSources(options: LoadConfigOptions = {}): Config {
       normalizedRaw.WORKSPACE_ROOT = resolve(cwd, normalizedRaw.WORKSPACE_ROOT);
     }
 
-  return ConfigSchema.parse(normalizedRaw);
+    return finalizeConfig(RawConfigSchema.parse(normalizedRaw), {
+      cwd,
+      pathEnv: env.PATH ?? process.env.PATH,
+    });
+  } catch (error) {
+    if (error instanceof DevflowError) {
+      throw error;
+    }
+
+    throw configInvalid(error);
+  }
 }
 
 function normalizeRawConfig(raw: Record<string, string | undefined>): Record<string, unknown> {
@@ -91,3 +102,101 @@ export function getConfig(): Config {
   cachedConfig ??= loadConfigFromSources();
   return cachedConfig;
 }
+
+function finalizeConfig(
+  value: RawConfig,
+  options: { cwd: string; pathEnv: string | undefined },
+): Config {
+  const canonicalWorkspaceRoot = realpathSync(resolve(value.WORKSPACE_ROOT));
+
+  return Object.freeze({
+    ...value,
+    WORKSPACE_ROOT: canonicalWorkspaceRoot,
+    backends: Object.freeze(normalizeBackends(value.backends, options)),
+  });
+}
+
+function normalizeBackends(
+  backends: BackendConfig[],
+  options: { cwd: string; pathEnv: string | undefined },
+): BackendConfig[] {
+  const normalized = backends.map((backend) => normalizeBackend(backend, options));
+  const hasFakeBackend = normalized.some((backend) => backend.id === "fake");
+
+  if (hasFakeBackend) {
+    return normalized;
+  }
+
+  return [freezeBackend({ id: "fake", enabled: true }), ...normalized];
+}
+
+function normalizeBackend(
+  backend: BackendConfig,
+  options: { cwd: string; pathEnv: string | undefined },
+): BackendConfig {
+  if (backend.id === "fake") {
+    return freezeBackend({ id: "fake", enabled: true });
+  }
+
+  if (!backend.enabled) {
+    return freezeBackend({ id: backend.id, enabled: false });
+  }
+
+  const resolvedPath = resolveBinaryPath(backend.binaryPath ?? backend.id, options);
+  if (resolvedPath === undefined) {
+    return freezeBackend({ id: backend.id, enabled: true });
+  }
+
+  return freezeBackend({ id: backend.id, enabled: true, binaryPath: resolvedPath });
+}
+
+function resolveBinaryPath(
+  binaryPath: string,
+  options: { cwd: string; pathEnv: string | undefined },
+): string | undefined {
+  if (binaryPath.includes("/")) {
+    const candidate = isAbsolute(binaryPath) ? binaryPath : resolve(options.cwd, binaryPath);
+    return executableRealpath(candidate);
+  }
+
+  for (const pathEntry of (options.pathEnv ?? "").split(delimiter)) {
+    if (pathEntry.length === 0) {
+      continue;
+    }
+
+    const candidate = resolve(pathEntry, binaryPath);
+    const resolved = executableRealpath(candidate);
+    if (resolved !== undefined) {
+      return resolved;
+    }
+  }
+
+  return undefined;
+}
+
+function executableRealpath(path: string): string | undefined {
+  try {
+    const resolved = realpathSync(path);
+    if (!statSync(resolved).isFile()) {
+      return undefined;
+    }
+
+    accessSync(resolved, constants.X_OK);
+    return resolved;
+  } catch {
+    return undefined;
+  }
+}
+
+function freezeBackend(backend: BackendConfig): BackendConfig {
+  return Object.freeze(backend);
+}
+
+function configInvalid(cause: unknown) {
+  return new DevflowError("config_invalid", {
+    class: "fatal",
+    code: "config_invalid",
+    cause,
+    recoveryHint: "Fix .env, .env.local, environment variables, and backend registrations.",
+  });
+}

packages/core/src/index.ts

@@ -1,4 +1,5 @@
 export * from "./config.js";
+export * from "./binding.js";
 export * from "./enums.js";
 export * from "./errors.js";
 export * from "./hash.js";