agentic-kvc/scripts/cache_aware_proxy.py

"""Unified cache-aware + token-level load-balanced global scheduler.

Supports two modes:
  --combined URL [URL ...]: PD co-located instances (normal vLLM, no KV transfer)
  --prefill URL BP --decode URL: PD disaggregated instances (Mooncake KV transfer)

Routing policies (--policy):
  linear (default): score = ongoing_tokens - ALPHA * cache_hit_tokens
  lmetric: score = P_tokens * BS  (LMetric, OSDI'26)
           P_tokens = pending_prefill_tokens + new_uncached_tokens
           BS = num_requests (waiting + running)
  Session affinity: multi-turn sessions stick to same instance (all policies).
"""

import argparse
import asyncio
import json
import os
import time as _time
import urllib.parse
import uuid
from collections import OrderedDict
from contextlib import asynccontextmanager
from dataclasses import dataclass

import httpx

MAX_STREAM_RETRIES = 3
RETRY_DELAY_S = 0.5
import uvicorn
from fastapi import FastAPI, HTTPException, Request
from fastapi.responses import StreamingResponse

BLOCK_SIZE = 512
CACHE_HIT_ALPHA = 1.0


@dataclass
class Settings:
    """Runtime-tunable knobs. Populated from argparse in __main__.

    All routing/offload code reads from the SETTINGS singleton so that
    CLI overrides survive even when the module is imported as a library
    (e.g. by tests/) and __main__ does not run.
    """
    prefill_throughput: float = 7000.0     # tokens/s per GPU (measured on H20)
    rdma_overhead_s: float = 0.1           # RDMA PUSH overhead (~10-50ms measured)
    cache_capacity_blocks: int = 200000    # per-instance LRU cap on shadow cached_blocks
    heavy_threshold: int = 20000
    overload_factor: float = 2.0
    max_offload_inflight: int = 4
    cache_gate_ratio: float = 0.0
    decode_iteration_s: float = 0.05      # per-request decode iteration cost (H20)


SETTINGS = Settings()


class InstanceState:
    def __init__(self, url: str, bootstrap_port: int | None = None):
        self.url = url
        self.bootstrap_port = bootstrap_port
        self.client = httpx.AsyncClient(
            timeout=None, base_url=url,
            limits=httpx.Limits(max_connections=None, max_keepalive_connections=None),
        )
        self.ongoing_tokens = 0
        self.ongoing_decode_tokens = 0  # subset: tokens in decode phase
        self.pending_prefill_tokens = 0  # tokens for requests still in prefill
        self.num_requests = 0  # total in-flight requests (waiting + running)
        self.active_p_offloads = 0  # number of HEAVY prefills this instance is doing for others
        self.engine_id: dict[int, str] = {}
        self.dp_size = 1
        # OrderedDict acts as an LRU keyed by block hash; value is unused.
        self.cached_blocks: OrderedDict[int, None] = OrderedDict()

    def estimate_cache_hit(self, token_ids: list[int] | None) -> int:
        if not token_ids or len(token_ids) < BLOCK_SIZE:
            return 0
        hit = 0
        for i in range(0, len(token_ids) - BLOCK_SIZE + 1, BLOCK_SIZE):
            bh = hash(tuple(token_ids[i:i + BLOCK_SIZE]))
            if bh in self.cached_blocks:
                self.cached_blocks.move_to_end(bh)  # LRU touch on hit
                hit += BLOCK_SIZE
            else:
                break
        return hit

    def record_prefix(self, token_ids: list[int] | None):
        if not token_ids:
            return
        for i in range(0, len(token_ids) - BLOCK_SIZE + 1, BLOCK_SIZE):
            bh = hash(tuple(token_ids[i:i + BLOCK_SIZE]))
            if bh in self.cached_blocks:
                self.cached_blocks.move_to_end(bh)
            else:
                self.cached_blocks[bh] = None
                if len(self.cached_blocks) > SETTINGS.cache_capacity_blocks:
                    self.cached_blocks.popitem(last=False)


def _p_offload_penalty(inst: InstanceState) -> int:
    """Penalty for PD-sep mode routing (legacy)."""
    if inst.active_p_offloads <= 0:
        return 0
    return inst.active_p_offloads * SETTINGS.heavy_threshold


def snapshot_workers(
    instances: list[InstanceState],
    token_ids: list[int] | None = None,
    input_length: int = 0,
) -> list[dict]:
    """Per-worker state at route-decision time.

    All routing-relevant counters plus the score each policy would
    have produced for `input_length` if it were dispatched now. Cheap
    enough to call on every request; B3 hot-spot analysis depends on
    this being captured per decision.
    """
    snap: list[dict] = []
    for i, inst in enumerate(instances):
        cache_hit = inst.estimate_cache_hit(token_ids) if token_ids else 0
        new_prefill = max(0, input_length - cache_hit)
        snap.append({
            "idx": i,
            "url": inst.url,
            "ongoing_tokens": inst.ongoing_tokens,
            "ongoing_decode_tokens": inst.ongoing_decode_tokens,
            "pending_prefill_tokens": inst.pending_prefill_tokens,
            "num_requests": inst.num_requests,
            "active_p_offloads": inst.active_p_offloads,
            "cached_blocks": len(inst.cached_blocks),
            "cache_hit": cache_hit,
            "new_prefill": new_prefill,
            "score_linear": (inst.ongoing_tokens
                              + _p_offload_penalty(inst)
                              - CACHE_HIT_ALPHA * cache_hit),
            "score_lmetric": (inst.pending_prefill_tokens + new_prefill)
                              * inst.num_requests,
        })
    return snap


def pick_instance(instances: list[InstanceState], token_ids: list[int] | None,
                  session_id: str | None, input_length: int,
                  affinity: dict[str, int]) -> tuple[InstanceState, int]:
    """Session-sticky with load-aware override.

    Turn 2+: use session affinity UNLESS pinned instance is overloaded
    or busy with P-role offloads, in which case pick least-loaded.
    Turn 1: pick instance with best score (load + cache combined).
    Instances doing P-role offloads get a large penalty to steer
    WARM/MEDIUM traffic away.
    """
    avg_load = max(sum(i.ongoing_tokens for i in instances) / len(instances), 1.0)

    if session_id and session_id in affinity:
        idx = affinity[session_id]
        if idx < len(instances):
            inst = instances[idx]
            if (inst.ongoing_tokens <= avg_load * SETTINGS.overload_factor
                    and inst.active_p_offloads == 0):
                return inst, idx

    best_idx, best_score = 0, float("inf")
    for i, inst in enumerate(instances):
        cache_hit = inst.estimate_cache_hit(token_ids)
        score = (inst.ongoing_tokens + _p_offload_penalty(inst)
                 - CACHE_HIT_ALPHA * cache_hit)
        if score < best_score:
            best_score = score
            best_idx = i

    if session_id:
        affinity[session_id] = best_idx
    return instances[best_idx], best_idx


def pick_instance_load_only(
    instances: list[InstanceState],
    token_ids: list[int] | None,
    session_id: str | None,
    input_length: int,
    affinity: dict[str, int],
) -> tuple[InstanceState, int]:
    """Pure load balancing: pick instance with fewest in-flight requests.

    Ignores cache hits and session affinity. Used as a B3 control to
    isolate the locality contribution of cache-aware policies.
    """
    best_idx = min(range(len(instances)),
                    key=lambda i: instances[i].num_requests)
    return instances[best_idx], best_idx


def pick_instance_sticky(
    instances: list[InstanceState],
    token_ids: list[int] | None,
    session_id: str | None,
    input_length: int,
    affinity: dict[str, int],
) -> tuple[InstanceState, int]:
    """Hard session affinity: once assigned, never break.

    First turn of a session picks the instance with the lowest
    num_requests; subsequent turns always return to the same instance
    regardless of load. Used as a B3 control to isolate the hot-spot
    cost of perfect locality.
    """
    if session_id and session_id in affinity:
        idx = affinity[session_id]
        if idx < len(instances):
            return instances[idx], idx
    best_idx = min(range(len(instances)),
                    key=lambda i: instances[i].num_requests)
    if session_id:
        affinity[session_id] = best_idx
    return instances[best_idx], best_idx


def pick_instance_lmetric(instances: list[InstanceState], token_ids: list[int] | None,
                          session_id: str | None, input_length: int,
                          affinity: dict[str, int]) -> tuple[InstanceState, int]:
    """LMetric routing: score = P_tokens × BS (OSDI'26).

    Pure per-request load-based routing, no session affinity (the
    session_id/affinity args are accepted for signature compatibility
    with pick_instance/pick_instance_unified_hybrid but ignored).
    P = pending_prefill_tokens + (input_length - cache_hit)
    BS = num_requests (current batch size)
    """
    best_idx, best_score = 0, float("inf")
    for i, inst in enumerate(instances):
        cache_hit = inst.estimate_cache_hit(token_ids)
        new_prefill = max(0, input_length - cache_hit)
        p_tokens = inst.pending_prefill_tokens + new_prefill
        bs = inst.num_requests
        score = p_tokens * bs
        if score < best_score:
            best_score = score
            best_idx = i

    return instances[best_idx], best_idx


_unified_fallback_rr_counter = 0


def pick_instance_unified_hybrid(
    instances: list[InstanceState],
    token_ids: list[int] | None,
    session_id: str | None,
    input_length: int,
    affinity: dict[str, int],
) -> tuple[InstanceState, int, dict]:
    """Hybrid routing: high-cache affinity, else LMetric with tie-breaker.

    Affinity gate (both must hold to stick):
      - affinity instance cache_hit / input_length > 0.5
      - affinity.num_requests <= avg_num_requests * SETTINGS.overload_factor

    Fallback ordering (when affinity not used):
      primary:   score = P_tokens * BS    (LMetric)
      secondary: new_uncached_tokens      (prefer instance with most cache)
      tertiary:  num_requests             (prefer least-loaded)
      quaternary: round-robin             (avoid degenerate inst-0 pinning
                                           when BS=0 across the board)

    Returns (chosen, idx, decision_dict). decision_dict carries the
    review #7 breakdown fields so the caller can merge them verbatim.
    """
    global _unified_fallback_rr_counter
    n = len(instances)
    avg_reqs = max(sum(i.num_requests for i in instances) / n, 1.0)

    decision: dict = {
        "decision": "lmetric_fallback",
        "affinity_idx": None,
        "chosen_idx": None,
        "affinity_cache_hit": None,
        "affinity_cache_ratio": None,
        "affinity_num_requests": None,
        "avg_num_requests": avg_reqs,
        "fallback_score": None,
        "tie_break_used": False,
    }

    if session_id and session_id in affinity:
        a_idx = affinity[session_id]
        if a_idx < n:
            a_inst = instances[a_idx]
            a_hit = a_inst.estimate_cache_hit(token_ids)
            a_ratio = a_hit / max(input_length, 1)
            decision["affinity_idx"] = a_idx
            decision["affinity_cache_hit"] = a_hit
            decision["affinity_cache_ratio"] = a_ratio
            decision["affinity_num_requests"] = a_inst.num_requests
            if (a_ratio > 0.5
                    and a_inst.num_requests <= avg_reqs * SETTINGS.overload_factor):
                decision["decision"] = "affinity"
                decision["chosen_idx"] = a_idx
                return a_inst, a_idx, decision

    keys: list[tuple[int, int, int, int]] = []
    for i, inst in enumerate(instances):
        cache_hit = inst.estimate_cache_hit(token_ids)
        new_prefill = max(0, input_length - cache_hit)
        p_tokens = inst.pending_prefill_tokens + new_prefill
        bs = inst.num_requests
        score = p_tokens * bs
        keys.append((score, new_prefill, bs, i))

    best_triple = min(k[:3] for k in keys)
    tied = [k for k in keys if k[:3] == best_triple]
    if len(tied) > 1:
        decision["tie_break_used"] = True
        _unified_fallback_rr_counter += 1
        winner = tied[_unified_fallback_rr_counter % len(tied)]
    else:
        winner = tied[0]
    chosen_idx = winner[3]
    decision["fallback_score"] = winner[0]
    decision["chosen_idx"] = chosen_idx
    return instances[chosen_idx], chosen_idx, decision


def _extract_output_token_ids_from_sse(
    buffer: str,
    chunk: bytes,
) -> tuple[str, list[int]]:
    """Extract vLLM streaming token_ids while preserving the raw stream."""
    buffer += chunk.decode("utf-8", errors="ignore")
    complete = buffer.endswith("\n") or buffer.endswith("\r")
    lines = buffer.splitlines()
    if complete:
        buffer = ""
    elif lines:
        buffer = lines.pop()
    else:
        return buffer, []

    output_ids: list[int] = []
    for line in lines:
        line = line.strip()
        if not line.startswith("data:"):
            continue
        data = line[5:].strip()
        if not data or data == "[DONE]":
            continue
        try:
            payload = json.loads(data)
        except json.JSONDecodeError:
            continue
        choices = payload.get("choices", [])
        for choice in choices:
            token_ids = choice.get("token_ids")
            if isinstance(token_ids, list):
                output_ids.extend(
                    int(t) for t in token_ids if isinstance(t, int)
                )
    return buffer, output_ids


def _realized_tokens(
    prompt_token_ids: list[int] | None,
    output_token_ids: list[int],
) -> list[int] | None:
    if prompt_token_ids is None:
        return None
    if not output_token_ids:
        return prompt_token_ids
    return prompt_token_ids + output_token_ids


global_args = None
combined_instances: list[InstanceState] = []
prefill_instances: list[InstanceState] = []
decode_instances: list[InstanceState] = []
# Session affinity is namespace-isolated: combined-mode and pd-sep mode index
# different instance lists, so a shared dict could mis-route after a mode switch.
session_affinity_combined: dict[str, int] = {}
session_affinity_prefill: dict[str, int] = {}
# Backwards-compat alias used by /stats etc.
session_affinity = session_affinity_combined
is_pd_sep = False
_breakdown_log: list[dict] = []
_worker_state_log: list[dict] = []


async def init_prefill_bootstrap(instances: list[InstanceState], ready: asyncio.Event):
    for inst in instances:
        if inst.bootstrap_port is None:
            continue
        while True:
            try:
                await inst.client.get("/health")
            except Exception:
                await asyncio.sleep(1)
                continue
            parsed = urllib.parse.urlparse(str(inst.client.base_url))
            url = f"http://{parsed.hostname}:{inst.bootstrap_port}/query"
            resp = await inst.client.get(url)
            resp.raise_for_status()
            data = resp.json()
            for dp_rank, dp_entry in data.items():
                inst.engine_id[int(dp_rank)] = dp_entry["engine_id"]
            inst.dp_size = len(data)
            print(f"Inited {inst.url} engine_ids={inst.engine_id}")
            break
    ready.set()


async def _reconcile_loop():
    """Periodic safety net for shadow state.

    StreamingResponse generators decrement load counters in their finally
    block, but if a client disconnects before the body is consumed the
    generator is never entered and the decrement is lost. Clamp negative
    drift every minute so router scores stay sane. This does not replace
    proper exact-state syncing with vLLM (see TODO.md item 6).
    """
    while True:
        try:
            await asyncio.sleep(60)
        except asyncio.CancelledError:
            return
        for inst in combined_instances + prefill_instances + decode_instances:
            if inst.ongoing_tokens < 0:
                inst.ongoing_tokens = 0
            if inst.ongoing_decode_tokens < 0:
                inst.ongoing_decode_tokens = 0
            if inst.pending_prefill_tokens < 0:
                inst.pending_prefill_tokens = 0
            if inst.num_requests < 0:
                inst.num_requests = 0
            if inst.active_p_offloads < 0:
                inst.active_p_offloads = 0


def _verify_vllm_patch():
    """Startup self-check for patches/0001-fix-kv-transfer-abort-race.patch.

    The patch turns an `assert req_id in self.requests` into a soft warn so
    that engines do not crash on the KV-transfer abort race (see REPORT
    §3.x). If somebody upgrades vLLM without re-applying the patch, the
    assert returns and elastic mode dies under load. Print a loud warning
    so we catch the regression before the first HEAVY request.
    """
    try:
        import inspect
        from vllm.v1.core.sched.scheduler import Scheduler
        src = inspect.getsource(Scheduler)
        if "assert req_id in self.requests" in src:
            print("WARNING: vLLM scheduler still contains the unpatched "
                  "`assert req_id in self.requests` line; expect engine "
                  "death on KV-transfer abort race. Apply "
                  "patches/0001-fix-kv-transfer-abort-race.patch.")
        else:
            print("vLLM patch self-check: kv-transfer-abort assert is patched.")
    except Exception as exc:
        print(f"vLLM patch self-check skipped: {exc!r}")


@asynccontextmanager
async def lifespan(app: FastAPI):
    global is_pd_sep
    app.state.ready = asyncio.Event()

    _verify_vllm_patch()

    reconcile_task = asyncio.create_task(_reconcile_loop())

    if global_args.combined:
        is_pd_sep = False
        bp_list = [int(p) for p in global_args.bootstrap_ports.split(",") if p.strip()] if global_args.bootstrap_ports else []
        for i, url in enumerate(global_args.combined):
            bp = bp_list[i] if i < len(bp_list) else None
            combined_instances.append(InstanceState(url, bp))

        # Bootstrap combined instances for offload (need engine_ids for KV transfer)
        if global_args.offload and bp_list:
            await init_prefill_bootstrap(combined_instances, app.state.ready)
        else:
            app.state.ready.set()

        policy = getattr(global_args, 'policy', 'linear')
        print(f"Combined mode: {len(combined_instances)} instances, policy={policy}, offload={'ON' if global_args.offload else 'OFF'}")
    else:
        is_pd_sep = True
        for url, bp in global_args.prefill:
            prefill_instances.append(InstanceState(url, bp))
        for url in global_args.decode:
            decode_instances.append(InstanceState(url))
        await init_prefill_bootstrap(prefill_instances, app.state.ready)
        print(f"PD-Sep mode: {len(prefill_instances)}P + {len(decode_instances)}D")

    yield
    reconcile_task.cancel()
    try:
        await reconcile_task
    except asyncio.CancelledError:
        pass
    for inst in combined_instances + prefill_instances + decode_instances:
        await inst.client.aclose()


app = FastAPI(lifespan=lifespan)


@app.post("/v1/completions")
async def handle_completions(request: Request):
    return await _handle(request, "/v1/completions")


@app.post("/v1/chat/completions")
async def handle_chat(request: Request):
    return await _handle(request, "/v1/chat/completions")


async def _handle(request: Request, api: str):
    if not app.state.ready.is_set():
        raise HTTPException(status_code=503, detail="Service Unavailable")

    req_data = await request.json()
    incoming_rid = request.headers.get("X-Request-Id")
    request_id = incoming_rid or str(uuid.uuid4())
    prompt = req_data.get("prompt")
    token_ids = prompt if isinstance(prompt, list) else None
    input_length = len(token_ids) if token_ids else 0
    session_id = request.headers.get("X-Session-Id")

    headers = {"X-Request-Id": request_id}
    api_key = os.environ.get("OPENAI_API_KEY")
    if api_key:
        headers["Authorization"] = f"Bearer {api_key}"

    if is_pd_sep:
        return await _handle_pd_sep(api, req_data, request_id, token_ids,
                                     input_length, session_id, headers)
    else:
        return await _handle_combined(api, req_data, token_ids,
                                       input_length, session_id, headers)


async def _handle_local_request(api, req_data, headers, token_ids, input_length,
                                chosen: InstanceState, estimated_new: int,
                                breakdown: dict):
    breakdown.setdefault("route_class", "LOCAL")
    breakdown.setdefault("routed_to", chosen.url)
    chosen.ongoing_tokens += input_length
    chosen.pending_prefill_tokens += estimated_new
    chosen.num_requests += 1

    async def generate():
        prefill_done = False
        sse_buffer = ""
        output_token_ids: list[int] = []
        try:
            for attempt in range(MAX_STREAM_RETRIES):
                try:
                    async with chosen.client.stream("POST", api, json=req_data, headers=headers) as resp:
                        resp.raise_for_status()
                        async for chunk in resp.aiter_bytes():
                            sse_buffer, new_output_ids = _extract_output_token_ids_from_sse(
                                sse_buffer, chunk)
                            output_token_ids.extend(new_output_ids)
                            if not prefill_done:
                                chosen.pending_prefill_tokens -= estimated_new
                                chosen.ongoing_decode_tokens += input_length
                                breakdown["t_first_token"] = _time.monotonic()
                                breakdown["t_first_token_unix"] = _time.time()
                                prefill_done = True
                            yield chunk
                    chosen.record_prefix(
                        _realized_tokens(token_ids, output_token_ids))
                    break
                except (httpx.ConnectError, httpx.RemoteProtocolError):
                    if prefill_done or attempt >= MAX_STREAM_RETRIES - 1:
                        raise
                    await asyncio.sleep(RETRY_DELAY_S)
        finally:
            if not prefill_done:
                chosen.pending_prefill_tokens -= estimated_new
            else:
                chosen.ongoing_decode_tokens -= input_length
            chosen.ongoing_tokens -= input_length
            chosen.num_requests -= 1
            breakdown["t_done"] = _time.monotonic()
            breakdown["t_done_unix"] = _time.time()
            _breakdown_log.append(breakdown)

    return StreamingResponse(generate(), media_type="text/event-stream")


async def _handle_combined(api, req_data, token_ids, input_length, session_id, headers):
    """Route a /v1/* request among combined (PD-colocated) instances.

    --policy options:
      linear:  cache_hit-aware load score + sticky session affinity.
      lmetric: P_tokens * BS (LMetric, OSDI'26). No session affinity.
      unified: hybrid — stick to affinity instance when cache_ratio > 0.5
               and it is not overloaded; otherwise fall back to LMetric
               with a multi-key tie-breaker.

    PD-sep offload / PUSH migration is retired (see REPORT.md §3.9 and
    commits 4c583f2 / cc6e562: relaxed-gate and forced-migration variants
    both regressed E2E tail). Re-enabling requires a new transfer mechanism.
    """
    policy = getattr(global_args, 'policy', 'linear')
    t_decision_unix = _time.time()
    request_id = headers.get("X-Request-Id", "")
    breakdown: dict = {
        "request_id": request_id,
        "session_id": session_id,
        "input_length": input_length,
        "t_proxy_recv": _time.monotonic(),
        "t_decision_unix": t_decision_unix,
        "policy": policy,
    }

    pre_decision_workers = snapshot_workers(
        combined_instances, token_ids, input_length)

    if policy == "lmetric":
        chosen, best_idx = pick_instance_lmetric(
            combined_instances, token_ids, session_id, input_length,
            session_affinity_combined)
    elif policy == "load_only":
        chosen, best_idx = pick_instance_load_only(
            combined_instances, token_ids, session_id, input_length,
            session_affinity_combined)
    elif policy == "sticky":
        chosen, best_idx = pick_instance_sticky(
            combined_instances, token_ids, session_id, input_length,
            session_affinity_combined)
    elif policy == "unified":
        chosen, best_idx, decision = pick_instance_unified_hybrid(
            combined_instances, token_ids, session_id, input_length,
            session_affinity_combined)
        breakdown.update(decision)
        if session_id:
            session_affinity_combined[session_id] = best_idx
    else:  # linear (default)
        chosen, best_idx = pick_instance(
            combined_instances, token_ids, session_id, input_length,
            session_affinity_combined)

    chosen_snap = pre_decision_workers[best_idx]
    cache_hit = chosen_snap["cache_hit"]
    estimated_new = chosen_snap["new_prefill"]
    breakdown.update({
        "cache_hit": cache_hit,
        "estimated_new_tokens": estimated_new,
        "route_class": "LOCAL",
        "routed_to": chosen.url,
        "chosen_idx": best_idx,
        "candidate_scores": pre_decision_workers,
        "chosen_score_linear": chosen_snap["score_linear"],
        "chosen_score_lmetric": chosen_snap["score_lmetric"],
    })

    _worker_state_log.append({
        "t_decision_unix": t_decision_unix,
        "request_id": request_id,
        "session_id": session_id,
        "policy": policy,
        "chosen_idx": best_idx,
        "workers": pre_decision_workers,
    })

    return await _handle_local_request(
        api, req_data, headers, token_ids, input_length,
        chosen, estimated_new, breakdown)


async def _handle_pd_sep(api, req_data, request_id, token_ids, input_length,
                          session_id, headers):
    """PD-Sep mode with per-stage breakdown profiling."""
    t_decision_unix = _time.time()
    breakdown = {
        "request_id": request_id,
        "session_id": session_id,
        "input_length": input_length,
        "t_proxy_recv": _time.monotonic(),
        "t_decision_unix": t_decision_unix,
        "policy": "pd_sep",
    }

    pre_decision_p = snapshot_workers(prefill_instances, token_ids, input_length)
    pre_decision_d = snapshot_workers(decode_instances, token_ids, input_length)

    p_inst, p_idx = pick_instance(prefill_instances, token_ids, session_id,
                                   input_length, session_affinity_prefill)
    d_idx = min(range(len(decode_instances)),
                 key=lambda i: decode_instances[i].ongoing_tokens)
    d_inst = decode_instances[d_idx]
    breakdown["p_inst"] = p_inst.url
    breakdown["d_inst"] = d_inst.url
    breakdown["candidate_scores_prefill"] = pre_decision_p
    breakdown["candidate_scores_decode"] = pre_decision_d
    breakdown["chosen_p_idx"] = p_idx
    breakdown["chosen_d_idx"] = d_idx

    _worker_state_log.append({
        "t_decision_unix": t_decision_unix,
        "request_id": request_id,
        "session_id": session_id,
        "policy": "pd_sep",
        "chosen_p_idx": p_idx,
        "chosen_d_idx": d_idx,
        "workers_prefill": pre_decision_p,
        "workers_decode": pre_decision_d,
    })

    prefill_data = req_data.copy()
    prefill_data["kv_transfer_params"] = {
        "do_remote_decode": True, "do_remote_prefill": False,
        "transfer_id": f"xfer-{request_id}",
    }
    prefill_data["stream"] = False
    prefill_data["max_tokens"] = 1
    prefill_data["min_tokens"] = 1
    prefill_data.pop("max_completion_tokens", None)
    prefill_data.pop("stream_options", None)
    p_headers = {**headers, "X-data-parallel-rank": "0"}

    p_inst.ongoing_tokens += input_length
    breakdown["t_prefill_sent"] = _time.monotonic()
    breakdown["t_prefill_sent_unix"] = _time.time()

    try:
        resp = await p_inst.client.post(api, json=prefill_data, headers=p_headers)
        breakdown["t_prefill_done"] = _time.monotonic()
        breakdown["t_prefill_done_unix"] = _time.time()
        resp.raise_for_status()
        await resp.aclose()
        p_inst.record_prefix(token_ids)
    except Exception as e:
        breakdown["t_prefill_done"] = _time.monotonic()
        breakdown["t_prefill_done_unix"] = _time.time()
        breakdown["prefill_error"] = True
        _breakdown_log.append(breakdown)
        raise HTTPException(status_code=502, detail=f"Prefill failed: {e}")
    finally:
        p_inst.ongoing_tokens -= input_length

    # Send decode
    d_inst.ongoing_tokens += input_length
    parsed = urllib.parse.urlparse(str(p_inst.client.base_url))
    bootstrap_addr = f"http://{parsed.hostname}:{p_inst.bootstrap_port}"

    decode_data = req_data.copy()
    decode_data["kv_transfer_params"] = {
        "do_remote_decode": False, "do_remote_prefill": True,
        "remote_bootstrap_addr": bootstrap_addr,
        "remote_engine_id": p_inst.engine_id.get(0, ""),
        "transfer_id": f"xfer-{request_id}",
    }

    breakdown["t_decode_sent"] = _time.monotonic()
    breakdown["t_decode_sent_unix"] = _time.time()

    async def generate():
        first_token = True
        sse_buffer = ""
        output_token_ids: list[int] = []
        try:
            async with d_inst.client.stream("POST", api, json=decode_data, headers=headers) as resp:
                resp.raise_for_status()
                async for chunk in resp.aiter_bytes():
                    sse_buffer, new_output_ids = _extract_output_token_ids_from_sse(
                        sse_buffer, chunk)
                    output_token_ids.extend(new_output_ids)
                    if first_token:
                        breakdown["t_first_token"] = _time.monotonic()
                        breakdown["t_first_token_unix"] = _time.time()
                        first_token = False
                    yield chunk
            d_inst.record_prefix(_realized_tokens(token_ids, output_token_ids))
        finally:
            breakdown["t_done"] = _time.monotonic()
            breakdown["t_done_unix"] = _time.time()
            d_inst.ongoing_tokens -= input_length
            _breakdown_log.append(breakdown)

    return StreamingResponse(generate(), media_type="application/json")


@app.get("/breakdown")
async def get_breakdown():
    """Return per-request breakdown data for analysis."""
    return _breakdown_log


@app.get("/worker_state")
async def get_worker_state():
    """Return per-decision worker-state snapshot log (one entry per route decision)."""
    return _worker_state_log


@app.get("/worker_state/latest")
async def get_worker_state_latest():
    """Return current per-worker state snapshot without recording it."""
    if combined_instances:
        return {
            "t_unix": _time.time(),
            "mode": "combined",
            "workers": snapshot_workers(combined_instances),
        }
    return {
        "t_unix": _time.time(),
        "mode": "pd_sep",
        "workers_prefill": snapshot_workers(prefill_instances),
        "workers_decode": snapshot_workers(decode_instances),
    }


@app.get("/stats")
async def get_stats():
    """Return per-instance live state for debugging."""
    instances = combined_instances or prefill_instances + decode_instances
    return [{
        "url": inst.url,
        "role": "combined",
        "ongoing_tokens": inst.ongoing_tokens,
        "pending_prefill_tokens": inst.pending_prefill_tokens,
        "ongoing_decode_tokens": inst.ongoing_decode_tokens,
        "num_requests": inst.num_requests,
        "active_p_offloads": inst.active_p_offloads,
        "cached_blocks": len(inst.cached_blocks),
    } for inst in instances]


def parse_args():
    p = argparse.ArgumentParser(description="Unified cache-aware global scheduler")
    p.add_argument("--port", type=int, default=8000)
    p.add_argument("--host", type=str, default="0.0.0.0")
    p.add_argument("--combined", nargs="+", help="Combined mode: list of instance URLs")
    p.add_argument("--prefill", nargs="+", action="append", dest="prefill_raw",
                   help="PD-Sep prefill: URL [bootstrap_port]")
    p.add_argument("--decode", nargs=1, action="append", dest="decode_raw",
                   help="PD-Sep decode: URL")
    p.add_argument("--heavy-threshold", type=int, default=20000,
                   help="New tokens threshold for HEAVY classification (adaptive offload)")
    p.add_argument("--offload", action="store_true",
                   help="Enable Mooncake KV offload for HEAVY requests (requires kv_both instances)")
    p.add_argument("--bootstrap-ports", type=str, default="",
                   help="Comma-separated bootstrap ports for combined instances (for offload mode)")
    p.add_argument("--policy", type=str, default="linear",
                   choices=["linear", "lmetric", "load_only", "sticky", "unified"],
                   help="Routing policy: linear (cache-aware), lmetric (P_tokens × BS), "
                        "load_only (B3 control: pure min-num_requests), "
                        "sticky (B3 control: hard session affinity), "
                        "or unified (hybrid affinity + LMetric fallback)")
    p.add_argument("--overload-factor", type=float, default=2.0,
                   help="Break session affinity when instance load > factor * avg")
    # The four flags below are accepted for bench.sh backward compatibility but
    # have no effect after the PD-sep offload path was retired (REPORT §3.9,
    # commits 4c583f2 / cc6e562). Removing them would break scripts/bench.sh and
    # scripts/legacy/*.sh which still pass them through.
    p.add_argument("--max-offload-inflight", type=int, default=4,
                   help="[DEPRECATED] PUSH offload retired; no effect")
    p.add_argument("--offload-mode", type=str, default="cached_prefill",
                   choices=["direct_read", "cached_prefill"],
                   help="[DEPRECATED] PUSH offload retired; no effect")
    p.add_argument("--cache-gate-ratio", type=float, default=0.0,
                   help="[DEPRECATED] PUSH offload retired; no effect")
    p.add_argument("--decode-iteration-s", type=float, default=0.05,
                   help="[DEPRECATED] PUSH offload retired; no effect")
    args = p.parse_args()

    args.prefill = []
    if args.prefill_raw:
        for entry in args.prefill_raw:
            url = entry[0]
            bp = int(entry[1]) if len(entry) > 1 and entry[1].lower() != "none" else None
            args.prefill.append((url, bp))
    args.decode = [e[0] for e in (args.decode_raw or [])]

    if not args.combined and not args.prefill:
        p.error("Must specify either --combined or --prefill/--decode")
    return args


if __name__ == "__main__":
    global_args = parse_args()
    SETTINGS.heavy_threshold = global_args.heavy_threshold
    SETTINGS.overload_factor = global_args.overload_factor
    SETTINGS.max_offload_inflight = global_args.max_offload_inflight
    SETTINGS.cache_gate_ratio = global_args.cache_gate_ratio
    SETTINGS.decode_iteration_s = getattr(global_args, 'decode_iteration_s', 0.05)
    print("SETTINGS: throughput=%.0f rdma_overhead=%.2f offload=%s" % (
        SETTINGS.prefill_throughput, SETTINGS.rdma_overhead_s,
        getattr(global_args, 'offload', False)))
    uvicorn.run(app, host=global_args.host, port=global_args.port)