Lossless Context MCP server

lossless-context-mcp

The flight recorder for your agent's context. A persistent, hook-fed ledger of every file version your coding agent was shown — so a compaction can't destroy the working set, a subagent fleet doesn't pay for the same files N times, and you can prove afterward exactly what the model saw.

┌──────────────────────┐
  ledger reads ──────▶│                      │──▶ RESTORE   working set survives /compact
  (read_file, MCP)    │   flight recorder    │──▶ PACKS     one cache-cached prefix for a fan-out fleet
  transcript sweeps ─▶│  (content-addressed  │──▶ RECEIPTS  signed, git-bound "what did it see"
  (native Read/Edit)  │   archive on disk)   │──▶ METERING  where the read tokens went, in dollars
                      └──────────────────────┘

See it

Compaction destroys your agent's working set. Not anymore — sweep at PreCompact, manifest injected after, blind edit blocked, working set restored, edit allowed:

Two agents, one file — air traffic control. The second agent is stopped mid-clobber, with the culprit named:

Every line in these recordings is genuine output from the shipped code — the demos are generated by docs/demo/make-demo.mjs, which drives the real hooks and server and renders what they actually said. Re-run it yourself.

1. Restore: compaction can't destroy your working set anymore

When Claude Code compacts, roughly two-thirds of a typical context is tool output — mostly file contents — and compaction discards it permanently. The model then flails: re-reading files it half-remembers, or worse, guessing at contents it no longer has (#27242 is the ask, at 80 👍).

The flight recorder closes the loop automatically:

the session touched (native Read/Edit/Write included, not just MCP reads), then writes a ranked working-set manifest. Fast enough to sit on the compaction path — one real 14 MB transcript swept in 361 ms; measure yours: node bench/sweep-bench.mjs .

1. PreCompact — the sweep hook parses the session transcript and archives every file

fresh context: "your working set was these 12 files (edited ones first); restore any of them instead of guessing."

1. SessionStart(compact) — the inject hook puts a compact manifest back into the

budget-capped, annotating any file that changed since the model last saw it.

1. restorecontext** — re-emits the working set from current disk state,

Cross-session memory tools (claude-mem and friends) summarize what happened for the next session. This is the complementary, mid-session layer: file-version-exact recovery of what you were just working on.

2. Blind-edit guard: the recorder as an active safety net

The recorder knows exactly which file versions the model has actually seen this context epoch. A PreToolUse hook uses that to stop the two ugliest edit failures before the write lands:

context was compacted/reset, working from a summary's memory of the content. (The harness's own read-before-edit tracking is not documented to survive compaction, and newer models are allowed to edit unread files at all.) Denied, with a one-line reason the model sees: read it (or restorecontext), then retry.* Self-healing — costs exactly one extra read.

• Post-compaction guess-edits — the model edits a file it hasn't read since its

agent, you, a formatter). Content-hash compared, not mtime-guessed. Denied with the same re-read instruction.

• Stale-base edits — the file changed on disk since the model read it (another

Shortened. The full README is on GitHub.