Session fails to load: strict schema validation rejects legacy `session.compaction_complete` events after upgrade to 1.0.35-3

[ericsciple]

Session fails to load: strict schema validation rejects older session.compaction_complete events

Summary

After updating to CLI 1.0.35-3, copilot --resume=<id> fails to load any session whose events.jsonl contains a session.compaction_complete event written by an earlier CLI version. The parser rejects the event instead of migrating/tolerating legacy shapes, which permanently bricks otherwise healthy sessions.

Version

• CLI: GitHub Copilot CLI 1.0.35-3
• OS: macOS (Darwin, arm64)
• Install: Homebrew cask (/opt/homebrew/bin/copilot)
• Pkg bundle in use: ~/.copilot/pkg/universal/1.0.35-3/sdk/index.js

Impact

• Many of my local sessions were unloadable after the upgrade (8 of 35 on this machine). All had valid, cleanly-shutdown events.jsonl files; only the compaction events were in the old shape.
• There is no UI recovery path: copilot --resume=<id> surfaces only No session or task matched '<id>'. The real parser error is only visible in ~/.copilot/logs/process-*.log.
• Nothing the user does (including ordinary actions like renaming a session summary) causes this — it's purely the CLI tightening the schema between versions.

Reproduction

1. Use a CLI version that writes compaction events with the old shape (keys under data.compactionTokensUsed are input, output, cachedInput).
2. Trigger an auto-compaction so at least one session.compaction_complete event lands in events.jsonl.
3. Upgrade to 1.0.35-3.
4. Run copilot --resume=<that-session-id>.

Expected: session loads (with or without a migration).
Actual: session fails to load; CLI reports "No session or task matched".

Log excerpt

[ERROR] Failed to parse session c00dcf1c-6727-4487-a3cf-c240cd486191:
  Error: Failed to read JSONL from .../events.jsonl:
  Error: Invalid event at line 785: data.compactionTokensUsed.inputTokens: Required.
  Event: {"type":"session.compaction_complete","data":{"success":true,"preCompactionTokens":135195,...
[ERROR] No session or task matched 'c00dcf1c-6727-4487-a3cf-c240cd486191'

Root cause

The session.compaction_complete schema changed key names and was tightened from optional to required. In ~/.copilot/pkg/universal/1.0.35-3/sdk/index.js:

zjo = be({
  inputTokens:      At().describe("Input tokens consumed by the compaction LLM call"),
  outputTokens:     At().describe("Output tokens produced by the compaction LLM call"),
  cacheReadTokens:  At().describe("Cached input tokens reused in the compaction LLM call"),
  cacheWriteTokens: At().describe("Tokens written to prompt cache in the compaction LLM call"),
  copilotUsage:     d9r.optional(),
  duration:         At().optional(),
  model:            V().optional(),
})

For comparison, the older bundled d.ts under ~/.copilot/pkg/universal/1.0.28/copilot-sdk/generated/session-events.d.ts still describes the legacy keys and marks compactionTokensUsed itself as optional:

compactionTokensUsed?: {
  input: number;
  output: number;
  cachedInput: number;
}

So legacy events look like:

{"compactionTokensUsed": {"input": 169241, "output": 3880, "cachedInput": 164955}}

…and the new parser rejects them because inputTokens is missing.

Suggested fixes (pick any)

1. Version / migrate legacy events on read. When parsing session.compaction_complete with old keys (input/output/cachedInput), map them to (inputTokens/outputTokens/cacheReadTokens) and default cacheWriteTokens to 0. This is a one-line normalization and preserves history.
2. Relax the schema. Make inputTokens/outputTokens/cacheReadTokens/cacheWriteTokens optional (they're telemetry anyway), or accept both legacy and new key shapes via a union.
3. Fail soft. If a single event fails validation, skip it (log a warning) rather than aborting the entire session load. The current behavior is a permanent data-loss risk whenever the schema evolves.
4. Surface the real error in the UI. Today users see only "No session or task matched", which suggests the session is missing; the actual parse error is log-only. At minimum print the underlying cause and the offending line.

Manual workaround (for the record)

Patching the offending events repairs the session. Back up first:

python3 - <<'PY'
import json, os, shutil
paths = [
  "/Users/<me>/.copilot/session-state/<id>/events.jsonl",
]
for p in paths:
    bak = p + ".bak"
    if not os.path.exists(bak):
        shutil.copy2(p, bak)
    out = []
    with open(p) as f:
        for line in f:
            if '"session.compaction_complete"' in line:
                e = json.loads(line)
                ctu = e.get("data", {}).get("compactionTokensUsed") or {}
                canon = {
                    "inputTokens":      ctu.get("inputTokens",      ctu.get("input", 0))      or 0,
                    "outputTokens":     ctu.get("outputTokens",     ctu.get("output", 0))     or 0,
                    "cacheReadTokens":  ctu.get("cacheReadTokens",  ctu.get("cachedInput", 0)) or 0,
                    "cacheWriteTokens": ctu.get("cacheWriteTokens", 0) or 0,
                }
                for k in ("copilotUsage", "duration", "model"):
                    if k in ctu:
                        canon[k] = ctu[k]
                e["data"]["compactionTokensUsed"] = canon
                line = json.dumps(e, ensure_ascii=False) + "\n"
            out.append(line)
    with open(p, "w") as f:
        f.writelines(out)
PY

Notes

• Affected sessions in my case both had a session.shutdown event at the end of events.jsonl — i.e., clean shutdowns, no corruption. Purely a schema-drift issue.
• I suspect any user who ran an older CLI, hit a long-enough conversation to trigger auto-compaction, and then upgraded to 1.0.35-x will have the same problem. Would be worth a one-shot migration on first launch of the new version.

[NStarkebaum]

Reproduced on Windows 11 / PowerShell 7 with CLI 1.0.35-3 (installed via WinGet). A session last written under an earlier 1.0.35-x build contained 4 session.compaction_complete events; resume failed with the schema error, one required field at a time:

• data.compactionTokensUsed.inputTokens: Required
• then cacheReadTokens: Required
• then cacheWriteTokens: Required

Confirms cross-platform impact and the strict additionalProperties: false behavior — legacy keys (input/output/cachedInput) also have to be removed, not just supplemented, or the next validator pass complains.

For Windows teammates, here's a PowerShell equivalent of the Python workaround. It scans every session under ~\.copilot\session-state\, rewrites compactionTokensUsed to the new shape (defaulting cacheWriteTokens to 0), and writes a .bak next to each modified file. Safe to re-run.

Get-ChildItem "$env:USERPROFILE\.copilot\session-state" -Recurse -Filter events.jsonl | ForEach-Object {
  $path = $_.FullName
  $lines = Get-Content $path
  $changed = $false
  for ($i = 0; $i -lt $lines.Count; $i++) {
    if ($lines[$i] -notmatch '"compactionTokensUsed"') { continue }
    $obj = $lines[$i] | ConvertFrom-Json
    $c = $obj.data.compactionTokensUsed
    if (-not $c) { continue }
    $names = $c.PSObject.Properties.Name
    if ($names -contains 'inputTokens' -and $names -contains 'cacheWriteTokens') { continue }
    $inp   = if ($names -contains 'input')       { $c.input }       elseif ($names -contains 'inputTokens')     { $c.inputTokens }     else { 0 }
    $out   = if ($names -contains 'output')      { $c.output }      elseif ($names -contains 'outputTokens')    { $c.outputTokens }    else { 0 }
    $cread = if ($names -contains 'cachedInput') { $c.cachedInput } elseif ($names -contains 'cacheReadTokens') { $c.cacheReadTokens } else { 0 }
    $new = New-Object PSObject
    Add-Member -InputObject $new -NotePropertyName inputTokens      -NotePropertyValue $inp
    Add-Member -InputObject $new -NotePropertyName outputTokens     -NotePropertyValue $out
    Add-Member -InputObject $new -NotePropertyName cacheReadTokens  -NotePropertyValue $cread
    Add-Member -InputObject $new -NotePropertyName cacheWriteTokens -NotePropertyValue 0
    $obj.data.compactionTokensUsed = $new
    $lines[$i] = ($obj | ConvertTo-Json -Depth 30 -Compress)
    $changed = $true
  }
  if ($changed) {
    Copy-Item $path "$path.bak" -Force
    Set-Content -Path $path -Value $lines -Encoding UTF8
    Write-Host "Patched: $path"
  }
}

+1 on the suggested fix of migrating legacy events on read — as the affected user, I had no signal anything was wrong until I tried to resume, by which point auto-compaction had already written events in the old shape. A one-shot migration on first launch of the new version would have avoided this entirely.

[dereklegenzoff]

Thanks for reporting! This issue was fixed in v1.0.35-4