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Moshe Avdiel
Moshe Avdiel

Posted on Originally published at github.com

Context Rot Hit at 25% of the Window and Grok Build Started Forgetting the Plan

I have sat next to the senses wall at 14:12 while Cursor was this close to calling the wrong MCP tool.

Not a model failure. A posture failure.

Context Rot: past ~25% window use, frontier models degrade. MCP dumps make that happen before work starts.

Someone on the floor said, out loud, the context is eating itself. Cursor had started earlier. The tool list was frozen in config.toml / .mcp.json / a skill file. The only “safe” move anyone trusted was:

  1. Kill Cursor (or its MCP child)
  2. Edit the server list
  3. Restart the host
  4. Lose the plan the model already paid for

That is the ceremony. After ~25% of a 1M window, quality falls; long MCP sessions perform like a worse model

The Aha: Compact/defer is posture. Set compact-mode=on live. Do not kill the session to 'clear context'. Real-time nested state is now a primitive — as native as a hashmap — via Kiponos.io. The host stays up. The leaf moves. The next tool call already obeys.

The problem: Compact mode as a live leaf when the window starts eating itself

Agentic programming in 2026 has a public fight: MCP vs CLI vs Skills. The likes on MCP and Grok Build posts are the tell. The industry is stuck on how to expose tools.

The missing primitive is live nested state:

Where the roster hid What you restart What you lose
MCP schema dump at session start The host, sometimes the child npx 16–72% of the window before the user speaks
~/.grok/config.toml / Cursor mcp.json Cursor The open turn
SKILL.md / AGENTS.md The next turn, sometimes the host Context you already bought
“Just reconnect the server” The MCP session Tool-space you finally had right

After ~25% of a 1M window, quality falls; long MCP sessions perform like a worse model

That is not a protocol bug you wait out. That is a process that cannot get() a tree that moved.

What teams believe

Belief Production
A bigger context window fixes tool overload 1M tokens still rot; selection still drops
Put the SDK in the SPA so the tile matches Connect tokens do not belong in a browser
Feature flags cover MCP write Flags are another product, another delay
Restart the agent host — it is cheap Cheap until 14:12 ate the open turn

What is Kiponos here

Kiponos is a live nested config hub. Dashboard edit → WebSocket delta → in-memory tree on every connected process. Hot-path get() is a local map lookup. One WebSocket per process lifetime.

It is not an MCP server. It is not a Skill. It is the control plane those things do not ship: which tools may run, how fat a result may be, whether execute is allowed, whether a child inherits posture — this turn.

Profile shape: ['my-app']['v1.0.0']['dev']['base']. The leaf in this story is compact-mode under examples/agentic-mcp-0909-am-context-rot/compact-mode.

Architecture

Architecture diagram

The model still calls tools. The wrapper reads compact-mode before the call. No schema dump policy in argv.

Config tree 

examples/agentic-mcp-0909-am-context-rot:
  compact-mode: off
  schema-budget: "4000"
  result-cap: "2000"
  tool-search: "on"
  execute-gate: "plan"
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Eight-plus keys when you pair compact-mode with sister dials (budget, mute, pause). They move together on the senses wall.

Integration

Java tool wrapper (Cursor just calls it):

import io.kiponos.Kiponos;
import io.kiponos.Folder;

Folder gate = Kiponos.createForCurrentTeam()
    .getFolder("examples/agentic-mcp-0909-am-context-rot");
String roster = String.valueOf(gate.get("compact-mode"));
// Cursor tool: refuse the dangerous MCP call when posture moved
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Python peer:

from kiponos import Kiponos

k = Kiponos.connect(quiet=True)
try:
    posture = k.get("examples/agentic-mcp-0909-am-context-rot/compact-mode", "live")
    if not str(posture):
        raise PermissionError("Compact mode as a live leaf when the window starts eating itself gated live — host not restarted")
finally:
    k.disconnect()
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React/Angular: Node BFF @kiponos/react/server / @kiponos/angular/server. SPA never holds Connect tokens.

Runnable mesh: https://github.com/kiponos-io/kiponos-io/tree/master/examples/java/agentic-mcp-0909-am-context-rot — ./gradlew test run.

Real scenarios

Event Without Kiponos With Kiponos
Three MCP servers at boot 72% of the window gone Live roster / schema-budget; dump shrinks
User says “no writes” mid-turn Restart Cursor Set compact-mode; next call already denies
Second host started earlier Paste the json into chat Both get() the same leaf
Subagent spawned Frozen argv copy Child get()s inherit-posture
Tool returns 500k tokens Context rot, doom loop result-cap in the wrapper

Performance (this path)

  • Wrapper get() is in-process after bootstrap.
  • One WebSocket per Cursor lifetime — not per MCP call.
  • A dashboard edit is a delta of compact-mode, not a config.toml reload.
  • You do not spend model tokens to “please restart Cursor.”
  • Schema tax is optional once the live set is small.

Compare to alternatives

Approach Honest fit Why it still restarts
More MCP servers More integrations More schema, worse selection
Skills progressive disclosure Good docs, lazy load Not a multi-host bus
Claude Code tool search Better client Other hosts still dump
Redis poll in the tool Shared, extra RTT You invented a hub with worse UX
Feature-flag SaaS Product experiments Rarely session-safe for MCP
Kill -9 the npx child Janitor The turn still died

When not to use Kiponos

Situation Why
Tool schema itself changed (new argument) That is a code/Cursor restart
Secret rotation of Connect / MCP OAuth tokens Credentials are not live knobs
One-off local script, no peers A hub is overkill
Browser-only “SDK in the SPA” Forbidden — tokens leak or defaults lie

Pair compact-mode with a sister dial

compact-mode rarely moves alone on the senses wall. Pair it with schema-budget, result-cap, or execute-gate so you do not fix Compact mode as a live leaf when the window starts eating itself by inventing a second incident.

Why Cursor is the wrong restart target

Cursor is good at calling tools. It is not a control plane. Killing it to flip compact-mode teaches the on-call that judgment requires a process ID. The senses wall already disagrees.

Getting started (15 minutes)

  1. TeamPro on kiponos.io → Connect → KIPONOS_ID / KIPONOS_ACCESS / profile ['my-app']['v1.0.0']['dev']['base'].
  2. Clone github.com/kiponos-io/kiponos-io.
  3. cd examples/java/agentic-mcp-0909-am-context-rot && cp kiponos.local.env.example kiponos.local.env
  4. ./gradlew test run — prints examples/agentic-mcp-0909-am-context-rot/compact-mode=...
  5. In the dashboard, change compact-mode. Keep Cursor up. No MCP reconnect.
  6. Point the tool wrapper at the same leaf. Do not ship a new server binary to flip Compact mode as a live leaf when the window starts eating itself.

Further reading

The moral

If flipping Compact mode as a live leaf when the window starts eating itself requires restarting Cursor or reconnecting MCP, you do not have agentic control. You have a hope with a process ID.

MCP, Skills, and tools are how agents act. Kiponos is the live primitive they do not ship — so the senses wall can change its mind without killing the session.

How to try: examples/java/agentic-mcp-0909-am-context-rot and ./gradlew test.

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