[docs] auth: docs: document AI-credit accounting for Copilot auto dynamic selector

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Summary

• Scan window: since 2026-08-20 (UTC). Reviewed README.md, docs/auth-matrix.md, docs/authentication-architecture.md, docs/api-proxy-sidecar.md, docs/environment.md, docs/awf-config-spec.md, docs/github_actions.md against containers/api-proxy/guards/ai-credits-guard.js, containers/api-proxy/guards/common-guard-checks.js, containers/api-proxy/token-budget-log.js, containers/api-proxy/token-tracker-shared.js, src/services/api-proxy-env-config.ts, src/services/api-proxy-credential-env.ts, src/services/agent-environment/excluded-vars.ts, src/services/agent-environment/env-passthrough.ts.
• Confirmed fix: isolate Actions OIDC from agent container #6894 (isolate Actions OIDC from agent container) is merged and its Actions-OIDC boundary documentation across docs/environment.md, docs/auth-matrix.md, and docs/authentication-architecture.md is accurate and current — no changes needed.
• Confirmed Ensure HTTP MCP GitHub OIDC bypasses the AWF agent credential boundary gh-aw#50053 (runner→gateway OIDC boundary) is resolved by Enforce runner→gateway OIDC path and prevent AWF agent exposure for HTTP MCP auth gh-aw#50054, and all three docs correctly state this and instruct recompiling lock files predating that change.
• Found a shipped-behavior gap: merged PR API proxy: first-class AI-credit accounting for Copilot auto dynamic selector #7604 ("API proxy: first-class AI-credit accounting for Copilot auto dynamic selector") added a dedicated accounting path in containers/api-proxy/guards/ai-credits-guard.js — the Copilot auto model (copilot:auto) is exempted from unknown_model_ai_credits rejection and instead priced with a conservative fallback ceiling, recorded via pricing_source/accounting_policy: dynamic_selector_fallback. docs/awf-config-spec.md §10.7.3 ("Unknown Model Rejection") documented the general reject/fallback behavior but never mentioned this recognized-selector exception, so a reader would wrongly expect auto requests to be rejected or require defaultAiCreditsPricing.
• Verified PR feat: support secret-backed OpenAI-compatible targets #7576 (secret-backed OpenAI-compatible targets, apiProxy.targets.openai.baseUrlEnv) is already fully documented in docs/awf-config-spec.md §9.7, docs/api-proxy-sidecar.md, and referenced correctly — no changes needed.
• Verified PRs Inject stable X-Interaction-Id and Copilot-Integration-Id on Copilot upstream requests #7545 (stable X-Interaction-Id/Copilot-Integration-Id headers) and [docs] auth: docs: document GITHUB_RUN_ID/GITHUB_RUN_ATTEMPT forwarding to api-proxy sidecar #7570 (documenting GITHUB_RUN_ID/GITHUB_RUN_ATTEMPT forwarding) are merged and already reflected in docs/auth-matrix.md and docs/api-proxy-sidecar.md — no changes needed.
• Verified PR Support Copilot Auto API endpoints #7554 (Copilot Auto API version injection) and its documentation PR [docs] docs: Update for Copilot Auto API versions and Cloud Hypervisor network readiness #7566 are merged and docs/auth-matrix.md already covers the /auto, /models/session, and /models/session/intent version-injection behavior accurately — no changes needed.
• Checked open PRs for [docs] auth: in the title — none open, so this is not a duplicate.

Documentation Changes

• docs/awf-config-spec.md (§10.7.3 Unknown Model Rejection): Added a "Recognized dynamic selectors" note stating that Copilot auto (copilot:auto) is exempt from unknown_model_ai_credits rejection, is priced via a conservative fallback ceiling instead, and lists the pricing_source/accounting_policy/pricing_tier/fallback_pricing_used/dynamic_selector fields set on its token-usage records. Clarifies this exception is scoped to the recognized Copilot auto selector only; other unresolved models keep the existing reject/fallback behavior.

Validation

• Verified containers/api-proxy/guards/ai-credits-guard.js implements getDynamicSelectorDescriptor/isRecognizedDynamicSelector scoped to provider === 'copilot' && model === 'auto', and DYNAMIC_SELECTOR_FALLBACK_PRICING/DYNAMIC_SELECTOR_FALLBACK_PRICING_SOURCE constants matching the documented field names.
• Confirmed test coverage exists in containers/api-proxy/guards/ai-credits-guard.test.js and containers/api-proxy/token-budget-log.test.js for this behavior.
• Ran npx markdownlint-cli2 docs/awf-config-spec.md — 0 issues.
• Reviewed the diff for token/key/JWT values and credential-bearing URLs — none present; only field/constant names.
• Confirmed no open PR with [docs] auth: in the title covers this finding.

Sources

• API proxy: first-class AI-credit accounting for Copilot auto dynamic selector #7604
• fix: isolate Actions OIDC from agent container #6894
• Ensure HTTP MCP GitHub OIDC bypasses the AWF agent credential boundary gh-aw#50053
• Enforce runner→gateway OIDC path and prevent AWF agent exposure for HTTP MCP auth gh-aw#50054
• containers/api-proxy/guards/ai-credits-guard.js, containers/api-proxy/guards/ai-credits-guard.test.js (repository source of truth)

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