FunctionGemma as a standalone DSL->StableHLO->IREE module - #302

Summary

• New :llm-inference:functiongemma module (the whisper/moonshine "one self-contained module" shape): FunctionGemmaSpec + FunctionGemmaContract (manifest.json emission) in commonMain, FunctionGemmaExportHarness + the exportFunctionGemma CLI/gradle task in jvmMain. Depends on :llm-inference:gemma for the architecture; owns the function-calling export/contract.
• The three-graph export (gemma redecode, gemma_prefill, gemma_with_past) is moved verbatim from :llm-runtime:kgemma's FunctionGemmaExport — golden-equivalence verified: all three exported MLIRs and all three safetensors archives are byte-identical (sha256) to the pre-move kgemma export on the same FunctionGemma-270M checkpoint.
• :llm-runtime:kgemma's FunctionGemmaExport/FunctionGemmaExportMain become @Deprecated delegating shims (deprecate-don't-delete); the pre-existing FunctionGemmaExportTest, FunctionGemmaInt8QuantTest, FunctionGemmaWithPastMlirDumpTest integration tests run unmodified against the shims and stay green. apiCheck is green (no public API change).
• :llm-runtime:gemma-iree gains manifest-driven support (D3): GemmaManifest (plain-JSON parse — intentionally no dependency on functiongemma, to keep gemma-iree's lean target set), GemmaKvDecoder.fromManifest(...) sourcing architecture constants/arg orders from the contract (existing hardcoded defaults preserved for direct-constructor callers), and CompactToolCodec.fromManifest(...) sourcing the tool vocabulary from the manifest's toolMap.
• Docker (skainet/iree-compiler:3.11.0) vmfb parity: gemma_prefill's compiled first token matches the board-verified oracle. Full multi-step greedy parity via x64 host-CPU run-module hit a pre-existing, non-regression divergence at the first generated special-vocabulary token — reproduces identically in bf16 and FP32, and independent of the KV-cache loop (a one-shot full-sequence forward reproduces it too), so it predates this move. Full diagnostic trail is in FunctionGemmaVmfbParityTest's class doc; flagged as a follow-up, not blocking.

Test plan

• Golden-equivalence: new module's export vs. pre-move kgemma export, byte-identical (sha256) MLIR + safetensors x3 graphs
• FunctionGemmaContractTest (pure, no checkpoint) — manifest arg/result order pinning
• FunctionGemmaExportDumpTest (real checkpoint) — MLIR signatures match the contract, manifest.json round-trips
• FunctionGemmaVmfbParityTest (real checkpoint + docker) — compile/convert-parameters/run-module succeed for all 3 graphs; prefill first-token oracle match
• GemmaManifestTest — manifest parsing + CompactToolCodec.fromManifest
• kgemma's pre-existing FunctionGemmaExportTest, FunctionGemmaInt8QuantTest, FunctionGemmaWithPastMlirDumpTest pass unmodified against the new shims
• :llm-runtime:kgemma:apiCheck green
• gemma-iree full jvmTest suite green (CompactCodec/ToolCallingSupport/ParserStrategy tests unaffected)

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