feat: AgentControl data model, parsing & interpolation (AIC-2662) (#171)

**Requirements**

- [x] I have added test coverage for new or changed functionality
- [x] I have followed the repository's [pull request submission
guidelines](../blob/main/CONTRIBUTING.md#submitting-pull-requests)
- [x] I have validated my changes against all supported platform
versions

**Related issues**

- Implements
[AIC-2662](https://launchdarkly.atlassian.net/browse/AIC-2662) — Step 2
of the Java AI SDK (epic
[AIC-2629](https://launchdarkly.atlassian.net/browse/AIC-2629)).
- Foundation (AIC-2661, #170) has merged; this PR is now based on
`main`.

**Describe the solution you've provided**

Step 2 of the Java AI SDK: the AICONF **data model** and the **defensive
JSON-protocol parsing** layer. No `LDAIClient` methods, tracker, or
evaluation (those are AIC-2663+).

> **Scope note:** Mustache interpolation has been **pulled out of this
PR**. Per the SDK team's supply-chain guidance we will not link the
external `com.samskivert:jmustache` artifact. The Mustache engine will
be **vendored** (source copied into an internal, relocated package)
together with the `Interpolator` in
[AIC-2695](https://launchdarkly.atlassian.net/browse/AIC-2695), which
gates the v1.0 release (AIC-2666). This PR therefore has **no
third-party templating dependency**.

_Public data model_ — `com.launchdarkly.sdk.server.ai.datamodel`
(immutable, builder-based, documented):
- `LDMessage` (`Role` enum + content), `ModelConfig`
(name/parameters/custom), `ProviderConfig`, `ToolConfig` (root-level
tool), `JudgeConfiguration` (+ nested `Judge`), and the `AIConfigMode`
enum.

_Internal parsing_ — `com.launchdarkly.sdk.server.ai.internal` (excluded
from published Javadoc/sources):
- `LDValueConverter` — depth-capped (`MAX_DEPTH = 100`) `LDValue` →
plain Java tree. Integral numbers within ±2^53 decode to `Long`,
otherwise `Double`.
- `AIConfigParser` + `AIConfigFlagValue` — `LDValue` → strongly-typed
parse. Malformed/missing/wrong-typed fields **never throw**; tools fall
back to `model.parameters.tools[]`; `evaluationMetricKey` resolves to
the first non-blank of `evaluationMetricKey` / `evaluationMetricKeys[]`;
`_ldMeta` scalars are boxed to preserve tri-state `enabled` (absent ≠
false).

**Design decisions (documented in code)**

- **Data-model placement:** kept in `...server.ai.datamodel` rather than
extracting a shared module now, to avoid premature abstraction; can
relocate if a client-side AI SDK ever needs it.
- **Boxed vs primitive:** `_ldMeta` scalars (`enabled`/`version`) are
boxed in the parsed value so "absent" is distinguishable from a concrete
value; resolved configs (later step) will use primitives with documented
defaults.
- **Number precision:** whole numbers outside ±2^53 cannot be
represented exactly and decode to the nearest `Double`.

**Additional context**

Field shapes and behaviors mirror the Python (`python-server-sdk-ai`)
and JS (`js-core/packages/sdk/server-ai`) reference SDKs for parity. 22
unit tests cover defensive parsing fallbacks and number/tool/metric-key
resolution; full module build (compile + checkstyle main/test + javadoc
+ tests) is green.

[AIC-2662]:
https://launchdarkly.atlassian.net/browse/AIC-2662?atlOrigin=eyJpIjoiNWRkNTljNzYxNjVmNDY3MDlhMDU5Y2ZhYzA5YTRkZjUiLCJwIjoiZ2l0aHViLWNvbS1KU1cifQ
[AIC-2629]:
https://launchdarkly.atlassian.net/browse/AIC-2629?atlOrigin=eyJpIjoiNWRkNTljNzYxNjVmNDY3MDlhMDU5Y2ZhYzA5YTRkZjUiLCJwIjoiZ2l0aHViLWNvbS1KU1cifQ
[AIC-2695]:
https://launchdarkly.atlassian.net/browse/AIC-2695?atlOrigin=eyJpIjoiNWRkNTljNzYxNjVmNDY3MDlhMDU5Y2ZhYzA5YTRkZjUiLCJwIjoiZ2l0aHViLWNvbS1KU1cifQ

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> New library surface and internal parsers only; no client evaluation or
runtime wiring yet, with broad unit test coverage for malformed
payloads.
> 
> **Overview**
> Adds the **Java server AI SDK data model and defensive flag-variation
parsing** for AI Configs (AIC-2662). Mustache interpolation is **not**
in this PR; `build.gradle` documents vendoring Mustache in AIC-2695
instead of linking `jmustache`.
> 
> **Public API** — New `LDAIConfigTypes` in `datamodel` groups immutable
nested types: `Mode`, `Message` (+ `Role`), `Model`, `Provider`, `Tool`,
and `JudgeConfiguration` (+ `Judge`), with builders where needed and
`Message.withContent` reserved for future interpolation.
> 
> **Internal parsing** — `AIConfigParser` maps `LDValue` →
`AIConfigFlagValue` without throwing on bad input; `LDValueConverter`
turns nested JSON into plain Java maps/lists with depth cap (`MAX_DEPTH
= 100`) and integral-number handling within ±2^53. Parsing covers
`_ldMeta` (boxed `enabled` for absent vs false), tools (root `tools`
over `model.parameters.tools[]`), and evaluation metric key (scalar then
first non-blank in `evaluationMetricKeys[]`).
> 
> **Build** — Javadoc no longer sets `failOnError = false` now that
public types exist; empty `sonatype*` entries removed from
`gradle.properties`. Unit tests cover parser and converter edge cases.
> 
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
69416f0. Bugbot is set up for automated
code reviews on this repo. Configure
[here](https://www.cursor.com/dashboard/bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

---------

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: ctawiah

lib/sdk/server-ai/build.gradle

@@ -45,9 +45,11 @@ ext.versions = [
     // The *lowest* version of the base SDK we are compatible with. LDClientInterface
     // appears in this library's public signature, so it is exposed as an `api` dependency.
     "sdk": "7.14.0"
-    // NOTE: a Mustache templating dependency (for AI Config message/instruction interpolation)
-    // will be added in a later step once it has been fully audited (license / maintenance /
-    // transitive deps). See AIC-2662.
+    // NOTE: the Mustache templating engine (for AI Config message/instruction interpolation) is
+    // intentionally not declared here. Per the SDK team's supply-chain guidance we will not link the
+    // external com.samskivert:jmustache artifact; the library will be vendored (source copied into an
+    // internal, relocated package) along with the Interpolator in AIC-2695, which must land before the
+    // v1.0 release (AIC-2666).
 ]
 
 ext.libraries = [:]
@@ -74,11 +76,6 @@ java {
 javadoc {
     // exclude internal implementation classes from the published API documentation
     exclude internalPackageGlob
-    // The foundation module (AIC-2661) intentionally ships no public types yet, only
-    // package-info.java. The javadoc tool reports "No public or protected classes found to
-    // document" in that state, so we tolerate it here. TODO(AIC-2662): set failOnError = true
-    // once the data-model public types land.
-    failOnError = false
     options {
         // suppress noisy "no comment" warnings; checkstyle enforces Javadoc on the public surface
         addStringOption('Xdoclint:all,-missing', '-quiet')

lib/sdk/server-ai/gradle.properties

@@ -1,8 +1,3 @@
 #x-release-please-start-version
 version=0.1.0
 #x-release-please-end
-
-# The following empty ossrh properties are used by LaunchDarkly's internal integration testing framework
-# and should not be needed for typical development purposes (including by third-party developers).
-sonatypeUsername=
-sonatypePassword=