feat(subagent): enforce transitive constraint propagation across delegation chains#4681
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…gation chains
Addresses constraint drift (arXiv:2605.10481): safety constraints set at
orchestration time were silently dropped when a subagent spawned its own
subagents, allowing trust-level and tool-allowlist escalation deep in
delegation chains.
Changes:
- Add `max_trust_level: Option<SkillTrustLevel>` and
`inherited_tool_allowlist: Option<HashSet<String>>` to `SpawnContext`
- Add `apply_constraint_propagation(def, ctx)` in zeph-subagent that:
- Clamps executor trust via `min_trust` (narrows only, never raises)
- Intersects AllowList with parent set; replaces InheritAll with parent set
- Converts DenyList to AllowList(parent \ deny_entries) when parent
allowlist is present (fail-closed)
- Logs constraint narrowing at `info` level for auditability
- Add `set_effective_trust` delegation in `FilteredToolExecutor` so the
cap reaches `PolicyGateExecutor` (previously hit the trait default no-op)
- Fix `PolicyGateExecutor::set_effective_trust` to clamp via `min_trust`
instead of unconditional assignment
Known limitation: the `resume()` path does not apply constraint
propagation; documented in source.
Closes #3993
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Summary
Fixes constraint drift (arXiv:2605.10481): safety constraints (
trust_level,tool_allowlist) set at orchestration time were silently dropped when a sub-agent spawned its own sub-agents, allowing trust and tool escalation deep in delegation chains.max_trust_levelandinherited_tool_allowlisttoSpawnContextapply_constraint_propagationnarrows executor trust viamin_trust(never raises) and intersects tool allowlistsFilteredToolExecutor::set_effective_trustnow delegates to innerPolicyGateExecutor(previously hit the trait default no-op)PolicyGateExecutor::set_effective_trustclamps viamin_trustinstead of unconditional assignmentAllowListinfolevel for auditabilityKnown limitation: the
resume()path does not apply constraint propagation (documented in source).Test plan
cargo build --workspacepassescargo clippy --workspace --features "desktop,ide,server,chat,pdf,scheduler" -- -D warnings— 0 warningscargo nextest run --workspace --lib --bins— 10327/10327 passCloses #3993