Add an optional, opaque `metadata` bag to tool definitions across all SDK
languages and forward it verbatim over the session.create/resume RPC. This
lets hosts attach namespaced metadata to tools without expanding the typed
public contract; the runtime may recognize specific keys to inform
host-specific behavior. Unknown keys are round-tripped untouched.

Languages: nodejs (Tool.metadata + defineTool), python (Tool.metadata +
define_tool), go (Tool.Metadata), rust (Tool.metadata + with_metadata),
java (ToolDefinition.metadata + createWithMetadata), dotnet
(CopilotToolOptions.Metadata + wire ToolDefinition.Metadata). Tests added
per language for wire/serialization forwarding and omission when unset.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

- dotnet: change Metadata value type to IDictionary<string, JsonNode?> for
  NativeAOT-safe serialization (CopilotToolOptions + wire ToolDefinition,
  FromAIFunction cast, unit test); drop redundant [JsonPropertyName("metadata")]
  since the Web camelCase policy already maps it; remove the <remarks> block
  from the Metadata property.
- Reword metadata doc comments across nodejs/python/go/rust/java to describe
  the bag opaquely without the SDK-vs-runtime/CLI distinction.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot-Session: bf2bf0dd-ec9f-42f5-a6e1-4f2a9e562d5f

Address Java SME feedback so annotation-based tools reach parity with the
programmatic API and existing constructor call sites keep compiling.

- ToolDefinition: add a backward-compatible 7-arg constructor delegating to
  the canonical 8-arg with metadata=null.
- CopilotTool: add metadata() plus nested MetadataEntry/MetadataValue/
  MetadataFlag annotations (@target({})) with a shallow bool|str|flag-map
  representation, documenting the programmatic API for richer values.
- CopilotToolProcessor: generate the metadata constructor argument
  (Map.<String, Object>of(...) with an explicit type witness) instead of a
  hardcoded null; null when no metadata is present.
- Tests: processor generation cases (nested flags, absent, combined flags),
  ToolDefinition 7-arg/.metadata(...) copy/flag-chaining cases, and a
  fromObject metadata assertion; extend the SimpleTools fixture pair to emit
  a safeForTelemetry metadata map.
- ADR-005: update the generated snippet to the 8-arg shape and document the
  @copilotTool(metadata = ...) syntax and emitted shape.

Note: mvn verify / spotless:apply not run locally (no JDK/Maven in the dev
environment); relies on PR CI.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot-Session: bf2bf0dd-ec9f-42f5-a6e1-4f2a9e562d5f

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot-Session: ab2c14cd-d2e1-4524-a6dc-e9c10899343c

test: assert null metadata arg in generated tool definition

…y state

Reword the 7-arg constructor's Javadoc to describe what the overload is (a
convenience constructor equivalent to the canonical one with metadata=null)
rather than its relationship to a specific change ("backward-compatible",
"retained so ... keep compiling after metadata was added"), which is only
meaningful in the context of the PR that introduced it.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot-Session: bf2bf0dd-ec9f-42f5-a6e1-4f2a9e562d5f

HashMap serializes keys in a randomized order, unlike the sibling `parameters`
field (IndexMap) and the other SDKs (nodejs/python insertion order, Go sorted).
Switch the tool `metadata` bag to IndexMap<String, Value> so key order is
deterministic and consistent, avoiding non-reproducible wire output. No new
dependency; indexmap is already used by this struct.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot-Session: bf2bf0dd-ec9f-42f5-a6e1-4f2a9e562d5f