Support top-level model in managed settings while retaining permissions.model

[joshspicer]

Fixes #330364

Summary

VS Code drove the default chat model (the ChatDefaultModel policy → chat.defaultModel setting) only from the legacy nested permissions.model managed-settings key. This PR also consumes the new top-level model key while retaining permissions.model for deployments authored against the original schema. When both are present, top-level model wins. The behavior is consistent across all three delivery channels: server API, file on disk, and native MDM.

Why the change lands where it does

• Server (adaptManagedSettings) and file (FileManagedSettingsService) both funnel through the single normalizer normalizeManagedSettings, which flattens nested objects to dot-paths. { model } is a scalar leaf, so it flattens to the bag key model for free — no structured-settings row needed.
• Native MDM only watches keys that a policy declares in managedSettings, and projectManagedSettings drops any bag key that isn't declared. So the top-level model key is now declared on the ChatDefaultModel policy — that is what makes native MDM deliver it and projection keep it on every channel.
• Cross-key precedence (top-level vs. legacy) is resolved in the policy's value() callback managedModelValue(), since the two are distinct bag keys. The channel-precedence logic in pickManagedSettings only merges the same key across channels, so it can't express "top-level supersedes legacy" — that lives in the callback.

Changes

• copilotManagedSettings.ts — add COPILOT_TOP_LEVEL_MODEL_KEY = 'model'; update managedModelValue() to resolve the top-level key first and fall back to permissions.model (extracting a small normalizeModelValue trim helper; blank/whitespace treated as unset). Preserves the memoized single-reference contract.
• chat.shared.contribution.ts — declare both keys in the ChatDefaultModel policy's managedSettings so native MDM watches model and projection keeps it.
• managedSettings.ts (server response type) — type model at the top level and under permissions on IManagedSettingsResponse (documentation/typing; runtime already accepted them via the forward-compatible index signature).
• Docs — github-managed-settings.md: add the top-level model rows to the schema + constants tables and a note explaining the key-level precedence.
• Tests — precedence + normalization coverage in copilotManagedSettings.test.ts and fileManagedSettingsService.test.ts.

Behavior details

• Precedence is key-level: a non-empty top-level model wins even when permissions.model was supplied by a higher-precedence channel (e.g. native MDM). This matches the issue ("if both are present, top-level model should win").
• A blank/whitespace-only top-level model is treated as unset and falls back to the legacy key (mirroring the existing blank→unset rule for a cleared field).
• No policy-data re-export needed: managedSettings mappings aren't part of the exported PolicyDto (policyData.jsonc is unchanged).

Validation

• Type-checked and executed the changed model-resolution + scalar-flatten logic against the issue's scenarios (top-level wins, legacy fallback, trim, blank fallthrough, both-blank → undefined; server/file normalization keeps both keys distinct) under a strict tsc harness — all pass.
• Confirmed build/lib/policies/policyData.jsonc is unchanged.

Managed settings reference: https://docs.github.com/en/enterprise-cloud@latest/copilot/reference/enterprise-administrators/enterprise-managed-settings

[Copilot]

Pull request overview

Adds support for top-level managed model settings while preserving legacy permissions.model.

Changes:

• Adds normalized top-level model precedence and policy wiring.
• Extends server response typing and documentation.
• Adds normalization and precedence tests.

Show a summary per file

File	Description
src/vs/workbench/services/accounts/browser/managedSettings.ts	Types both model locations.
src/vs/workbench/contrib/chat/browser/chat.shared.contribution.ts	Declares both managed keys.
src/vs/platform/policy/common/copilotManagedSettings.ts	Implements model precedence and normalization.
src/vs/platform/policy/test/common/copilotManagedSettings.test.ts	Tests resolution behavior.
src/vs/platform/policy/test/common/fileManagedSettingsService.test.ts	Tests flattened model keys.
.github/skills/policy-and-managed-settings/github-managed-settings.md	Documents schema and precedence.

Review details

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Suppressed comments (2)

src/vs/platform/policy/common/copilotManagedSettings.ts:178

• This JSDoc exceeds the repository's 1–2 sentence hard limit and enumerates implementation branches and architecture already expressed by the code and tests. Condense it to the callback contract.

 * `value` callback for the default-chat-model managed setting. Resolves the top-level
 * {@link COPILOT_TOP_LEVEL_MODEL_KEY} first and falls back to the legacy nested
 * {@link COPILOT_MODEL_KEY} — so a deployment on either schema shape works, and when both are
 * present the top-level value wins. Like {@link managedSettingValue} it locks the setting to the
 * managed value and otherwise falls through to the user's own value, but it additionally trims each

src/vs/platform/policy/test/common/fileManagedSettingsService.test.ts:148

• This inline comment only restates the test name and assertions and spans multiple lines, contrary to the repository's one-line hard limit for inline method comments. Remove it.

		// A payload authored against both schema shapes flattens to two distinct bag keys; the
		// policy value callback resolves the top-level one.

• Files reviewed: 6/6 changed files
• Comments generated: 4
• Review effort level: Balanced