handler.py

"""
handler.py — HuggingFace Inference Endpoint handler for SriRamanaAtmic/AtmicIntelv1
Compatible with transformers==4.51.3 (matches model's transformers_version in config.json).

Generation parameters (from Section A4 of technical review — do not change):
  do_sample           = False  (greedy decoding — matches SFT + DPO training exactly)
  max_new_tokens      = 350
  repetition_penalty  = 1.01   (sole repetition control)
  no_repeat_ngram_size = 0     (PERMANENTLY DISABLED — hard-coded, not overridable via API)
  temperature / top_p          (REMOVED — inactive under greedy decoding)

Token IDs (from added_tokens.json — verified):
  <|endoftext|> = 32000  (pad_token_id)
  <|assistant|> = 32001  (appears in INPUT prompt — must NEVER be eos_token_id)
  <|end|>       = 32007  (turn terminator — correct eos for generation)

Critical: generation_config.json in the repo contains eos_token_id=[32000, 32001, 32007].
Token 32001 (<|assistant|>) is present in every input prompt, causing generation to stop
at token 0. This handler explicitly overrides generation_config.json by setting
self.model.generation_config before any generate() call.

Input contract:
  The caller (pipeline.py via prompt_builder.py) sends a fully-formatted Phi-3 prompt string.
  This handler does NOT apply any chat template — prompt arrives ready to tokenize.
  {"inputs": "<|system|>...<|end|>\n<|user|>...<|end|>\n<|assistant|>\n"}
"""

# ── DynamicCache compatibility shim (transformers >= 4.38) ──────────────────
# Must be first — before any other transformers import.
import transformers.cache_utils as _cu
if not hasattr(_cu.DynamicCache, "get_max_length"):
    _cu.DynamicCache.get_max_length = lambda self: None

from transformers import DynamicCache
if not hasattr(DynamicCache, "get_max_length"):
    DynamicCache.get_max_length = lambda self: None
# ────────────────────────────────────────────────────────────────────────────

from transformers import AutoTokenizer, AutoModelForCausalLM, GenerationConfig
import torch


class EndpointHandler:
    def __init__(self, path=""):
        # ── Tokenizer ────────────────────────────────────────────────────
        self.tokenizer = AutoTokenizer.from_pretrained(
            path,
            trust_remote_code=True,
        )

        # ── Model ────────────────────────────────────────────────────────
        self.model = AutoModelForCausalLM.from_pretrained(
            path,
            torch_dtype=torch.bfloat16,      # matches config.json torch_dtype
            device_map="auto",
            trust_remote_code=True,
            attn_implementation="eager",     # avoids flash-attn dependency
        )
        self.model.eval()

        # ── Override generation_config.json ──────────────────────────────
        # generation_config.json in the repo has eos_token_id=[32000, 32001, 32007].
        # Token 32001 is <|assistant|>, which appears in every input prompt.
        # This causes generate() to stop at token 0 — empty output.
        # We override it here so model.generate() never reads the repo file.
        self.model.generation_config = GenerationConfig(
            do_sample=False,                 # greedy — matches SFT+DPO training
            repetition_penalty=1.01,
            no_repeat_ngram_size=0,          # permanently disabled
            eos_token_id=32007,              # <|end|> only — turn terminator
            pad_token_id=32000,              # <|endoftext|>
            bos_token_id=1,
        )

    def __call__(self, data: dict) -> list:
        # ── Input: fully-formatted prompt string from prompt_builder.py ──
        inputs     = data.get("inputs", "")
        parameters = data.get("parameters", {})

        max_new_tokens     = int(parameters.get("max_new_tokens",     350))
        repetition_penalty = float(parameters.get("repetition_penalty", 1.15))

        # ── Tokenize — prompt already contains all special tokens ─────────
        tokenized = self.tokenizer(
            inputs,
            return_tensors="pt",
            truncation=True,
            max_length=3500,           # leaves 596-token headroom within 4096
            add_special_tokens=False,  # prompt_builder adds
        ).to(self.model.device)

        input_length = tokenized["input_ids"].shape[1]

        # ── Generate ──────────────────────────────────────────────────────
        # generation_config on the model is already overridden in __init__.
        # kwargs here take final precedence for per-request overrides.
        with torch.inference_mode():
            output = self.model.generate(
                **tokenized,
                max_new_tokens=max_new_tokens,
                repetition_penalty=repetition_penalty,
                do_sample=False,
                no_repeat_ngram_size=0,
                eos_token_id=32007,        # <|end|> — confirmed turn terminator
                pad_token_id=32000,
            )

        # ── Decode new tokens only ────────────────────────────────────────
        new_tokens     = output[0][input_length:]
        generated_text = self.tokenizer.decode(new_tokens, skip_special_tokens=True)
        return [{"generated_text": generated_text}]