Add AI-assisted policy evaluation backend to Expense Agent

[encimita]

Fixes AB#626515

Motivation

Expenses have hard rules in code and soft policies evaluated with AI. This moves policy-flag management to the backend so clients don't need bespoke APIs to configure policies, while still allowing them to read violations and detect whether the capability is supported.

This supersedes NAV PR 251762 after Expense Agent moved from NAV to BCApps.

Design

Subject: Expense Report Line - The report line is the sole policy subject. It is a creation-time snapshot of an expense, and its content and child details determine policy relevance.

Status and version model - GetPolicyStatus() returns Not Evaluated, Stale, Flagged, or Cleared. Policy Eval Version tracks the report line generation and is bumped by relevant line edits, child changes, and applicable policy changes. Evaluated Policy Version records the generation last evaluated by the agent. Version 0 is a normal version, not a sentinel.

Lines with no applicable policies are treated as Cleared without requiring an evaluation pass.

Expense Policy Flag - Flags retain evaluation history using (Subject System Id, Policy System Id, Subject Version, Policy Version). The server stamps Subject Version from the report line, and Policy Version snapshots the policy version. Is Current indicates whether the policy has changed since the flag was written. Duplicate evaluations for the same versions fail by design.

Expense Policy - Policies use (Subject Type, Line No.) as the primary key, with category as a secondary key and a bumpable version field. Adding, changing, or deleting an applicable policy invalidates evaluated report lines. A blank category applies to all categories.

Invalidation - Relevant report-line edits, participant/itemization/per-diem changes, and applicable policy changes bump the subject version. Relevant-field detection reads the committed pre-modify image from the database rather than relying on xRec.

Submitting a report is non-invalidating because release and approval state changes only affect the header.

API changes

• Add markPoliciesEvaluated to Expense Report Lines API.
• Add the read/insert expensePolicyFlags subpage scoped to the current subject version.
• Add read-only policyStatus and policiesEvaluatedAt.
• Add the nested read-only policiesToEvaluate endpoint for policies still requiring evaluation at the current subject and policy versions.
• Add submit-with-comment overloads to Expense Reports API.
• Add a read-only Posted Expense Policy Flags API nested under Posted Expense Report Lines.
• Add AiAssistedPolicyEvaluation to the Expense Capability enum.

Posting and setup

Posting copies current-version flags to the immutable Posted Expense Policy Flag table for audit. Deleting an open report line removes its flags.

The setup wizard includes an Evaluate Policies option gated by AI credits and opens Expense Policies modally.

Testing

The migrated changes include regression coverage for policy status, line and child invalidation, policy add/change/delete invalidation, evaluation history, duplicate evaluation protection, submit safety, posting, and the policiesToEvaluate endpoint.

The original NAV implementation compiled and its focused policy-flag suite passed on a live NST. The migrated BCApps branch has not yet been compiled or run through the BCApps pipeline.

[encimita]

Review completed against backend, testing, and code-diet lenses. Four blocking defects and four suggestions are attached inline.