feat(candidate): add immutable agent bundle contract

[drewstone]

What

• define a versioned sealed candidate that carries a strict profile, explicit disabled/no-op/changed source state, content-addressed resources, and the complete built executable workspace
• represent optimizer-produced prompt, skill, knowledge, memory, and code candidates without inventing a code change or collapsing a proposer no-op into a control
• forbid candidate credentials, ambient connections, remote MCP, network access, opaque routing metadata, and alternate model routes in V1
• define canonical profile and per-task execution documents that bind repository ancestry, split, task and candidate workspaces, profile target paths, exact container bytes, exact model snapshot and effort, counted attempts, retry policy, tool-step and spend limits, evaluator authorization, and fresh task memory
• define materialization and run receipts that bind those documents to exact entrypoint bytes, non-empty trace evidence, one-model usage, truthful termination, and memory state
• reject unsafe paths and private OCI targets, non-regular workspace entries, unsupported profile behavior, ambiguous controls, false proposer no-ops, incomplete model identities, usage/trace disagreement, and cross-receipt mismatches

schema.parse() proves the strict wire shape. @tangle-network/agent-runtime recomputes canonical identities, verifies every artifact and workspace byte, mediates model access, and fails closed before execution.

Verification

• pnpm check-types (8 packages)
• pnpm test (521 tests)
• pnpm build (8 packages)
• mutation probes: OCI numeric-loopback and unsupported-profile regressions fail when their fixes are removed
• git diff --check
• git merge-tree --write-tree origin/main HEAD

Existing primitives extended

The change extends the canonical AgentProfile, HarnessType, and Zod schema surfaces in @tangle-network/agent-interface; it does not duplicate runtime materialization or evaluation logic.