Provider permissions: tier resolution engine

[jeonghun-jj-lee]

Important

Decision Surface

Problem: No runtime logic exists to resolve a model's effective permissions from its trust tier assignment.

Approach: Implement resolveProviderPermission(modelId, action, resource) — looks up model → tier → directory rules → effect. Most-specific glob wins. O(1) tier lookup via pre-built map.

Scope: Resolution engine only. Does not wire into the permission system (that is slice #4).

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Acceptance Criteria

• resolveProviderPermission(modelId, action, resource) returns the correct Effect for any model/action/resource combination
• Unassigned models (not in assignments) resolve against the defaultTier
• Most-specific glob wins: ~/secrets/** takes priority over ** for paths under ~/secrets/
• Action mapping is correct: read action resolves against the read group, glob/grep also resolve against read; write/edit against write; bash against execute; webfetch/websearch against network
• Tier lookup is O(1) — uses a pre-built Map<tierId, TrustTier> not a list scan
• Returns undefined when no rule matches (signals fallthrough to existing permission system)

Key Decisions

#	Decision	Rationale
1	Pre-build a Map<tierId, TrustTier> at config parse time	O(1) lookup per tool call
2	Return undefined for no-match (not "ask")	Lets the enforcement hook distinguish "no opinion" from "explicitly ask"
3	Glob specificity by pattern length (longest match wins)	Simple, predictable, matches user mental model

Testing Decisions

• Test model in "trusted" tier gets "allow" for all actions
• Test model in "limited" tier gets "allow" for read, "deny" for write/execute/network
• Test unassigned model falls through to default tier
• Test most-specific-glob precedence (specific dir rule overrides wildcard)
• Test action-to-group mapping (grep → read, edit → write, bash → execute, webfetch → network)
• Test returns undefined when tier has no matching directory rule

Constraints & Invariants

• Pure function with no side effects — stateless resolution from config
• Must handle the case where a model's assigned tier ID no longer exists in config (treat as unassigned)

Source

Part of #163
Blocked by #164