Bug: v0-to-v1 migrator rejects subagent/descriptor version 2 written by earlier releases, breaking session search

[silence201991]

Environment

• dsh 0.1.5-rc.2 (upgraded from 0.1.0-rc.7), Windows
• session-query-sqlite with openAt: first-search

Summary

After upgrading, every session search fails. Both searchSessions and searchEvents run the
same global reconcile step, so a single un-migratable session breaks the whole feature.

Steps to reproduce

1. Have sessions written by 0.1.0-rc.7 in which a subagent was spawned — they contain
   subagent/descriptor records with data.version === 2.
2. Upgrade to 0.1.5-rc.2.
3. Call the session search service (searchSessions({ query, limit })), or any plugin tool
   that wraps it (here: session_search).

Actual

session-search persistence observation failed:
subagent/descriptor 0 uses unsupported descriptor version 2;
source v0 artifact remains unchanged (raw log: ...\session.jsonl.zstd)

Expected

Legacy sessions migrate, or are skipped with a warning, and search over the remaining
sessions keeps working.

Root cause

Two gates, both keyed on the descriptor version. (Line numbers are from the published package
build, lib/index.js; the function names are the stable part.)

1) dsh-session-format-v0-to-v1, the v0-to-v1 migrator:

if (event.type === "subagent/descriptor" && data["version"] !== 3) {
  const descriptorVersion = sessionFormatCount(data["version"], `${event.type} ${event.seq} version`);
  if (version === 0) throw new SessionFormatUnsupportedMigrationError(
    `${event.type} ${event.seq} uses unsupported descriptor version ${descriptorVersion}`);
  return;
}

2) dsh-session-format-v0-to-v1, subagentDescriptorValue() — reached through
assertReleasedPayloadSemantics(), which dsh-session-format-v2-to-v3 imports directly
(line 3 of that package):

literalValue(data["version"], [3], `${label} version`);

Relaxing gate 1 alone only moves the failure to gate 2:

@deepseek-ai/dsh-session-format-v2-to-v3 refuses this format v2 Session:
subagent/descriptor 0 version must be one of 3

Earlier releases wrote descriptor version 2, and neither gate has a v2 branch.

Measured payload shapes of the version-2 records (76 records)

• 49 × continuable: mode, provider, version, label, agentProvider, agentModel
  (the agent pair is complete)
• 27 × one-shot: mode, provider, version, optional label

They satisfy every other field check, so the version literal is the only rejection.

Impact (measured on my machine)

163 v0 session files; 76 contain subagent/descriptor records; all 76 are version 2 and none
are version 3. Session search was therefore 100% unavailable rather than occasionally failing.
The failed migration leaves the source artifact unchanged, so no data is lost.

Local verification

Relaxing both gates locally ([3] → [2, 3], and not throwing in the generation-0 branch)
restores search immediately: all 76 legacy artifacts then pass validation, search returns hits
from the previously un-migratable sessions, and 162 of the 163 source files are byte-identical
by SHA-256 (the one change is the live session log being written).

Suggested fix

• Accept descriptor version 2 alongside 3 at both gates, or add a proper v2 normalization branch.
• More importantly: make observation resilient — skip an artifact that cannot be migrated, with a
  warning, instead of failing the global reconcile that both searchSessions and searchEvents
  depend on. One legacy session should not be able to disable the whole query service.