feat(agent-profile-cell): AGENT_PROFILE_KINDS + toAgentProfileJson + buildSandboxAgentProfileCell

[drewstone]

Closes #82.

What

Two pieces of boilerplate every product consuming buildAgentProfileCell has been duplicating — gtm-agent#137, blueprint-agent#1756 / #1757:

1. A JSON.parse(JSON.stringify(value)) helper that canonicalizes an arbitrary sandbox-SDK AgentProfile into AgentProfileJson, with a fail-loud error when the profile is not JSON-serializable.
2. The magic string 'sandbox-agent-profile' for sourceProfile.kind.

Both belong here so the cross-product cell join (same canonical profile hashes to the same sourceProfile.hash across products) is enforced by the type system, not by every consumer remembering to do it right.

API additions

export const AGENT_PROFILE_KINDS = {
  SANDBOX_AGENT_PROFILE: 'sandbox-agent-profile',
} as const
export type AgentProfileKind = (typeof AGENT_PROFILE_KINDS)[keyof typeof AGENT_PROFILE_KINDS]

export function toAgentProfileJson(value: unknown): AgentProfileJson

export interface SandboxAgentProfileLike { name: string; version: string; [key: string]: unknown }

export async function buildSandboxAgentProfileCell(
  profile: SandboxAgentProfileLike,
  input: Omit<AgentProfileCellInput, 'profileId' | 'sourceProfile'>,
): Promise<AgentProfileCell>

buildSandboxAgentProfileCell is the higher-level wrapper — hard-codes profileId = \${name}@${version}`and thesandbox-agent-profilekind. The manualbuildAgentProfileCell` call stays for advanced cases (custom kinds, pre-computed source hashes, alternate profileId conventions).

Verification

• tsc --noEmit clean.
• Package suite: 1317/1317 pass (11 new tests for the helpers).
• Cross-product invariant explicitly tested: a hand-rolled buildAgentProfileCell call following the documented README recipe produces the identical sourceProfile.hash + cellId as buildSandboxAgentProfileCell. Two products converging on this helper are guaranteed to hash the same canonical profile identically.

Downstream

• gtm-agent's eval/agent-profile-cell.ts can delete its local toAgentProfileJson and import the canonical one.
• blueprint-agent's scripts/experiments/lib/agent-profile-cell.ts (currently shipping its own sandboxAgentProfileToJson + the magic string) will follow up with a PR collapsing the duplication.