Problem

Compaction/reset paths can break session invariants in two related ways:

1. hook contexts can lose or mis-normalize messageProvider
2. successful compaction can leave stale token/cost accounting behind

In practice this causes downstream consumers to see one real conversation as multiple logical sessions, and can also trap a session in repeated compaction safeguard loops after the transcript has already been cleared.

Concrete affected paths

Today this cluster shows up across several connected paths:

1. auto compaction hook dispatch via handleAutoCompactionStart/End
2. engine-owned compaction hook dispatch in compact.queued.ts
3. command reset hooks via emitResetCommandHooks
4. gateway sessions.reset via emitGatewayBeforeResetPluginHook
5. post-compaction session accounting when tokensAfter === 0

Reproduction A: provider invariants

1. Use a channel-scoped session key like agent:main:feishu:default:direct:ou_xxx
2. Register a plugin that uses ctx.sessionKey + ctx.messageProvider to build stable session identity
3. Trigger auto compaction, /new, /reset, or sessions.reset
4. Observe ctx.messageProvider missing, mixed-case, or inferred from a non-channel key shape
5. Plugin falls back to unknown or treats Telegram / telegram as different providers
6. One real conversation is split into multiple logical sessions

Reproduction B: token accounting invariants

1. Start a long-running session that reaches compaction
2. Let compaction collapse the remaining transcript to an effectively empty/zero-token state
3. Observe the transcript is cleared but cached accounting still reports old totals
4. Next turn hits the compaction safeguard again because totalTokens / cost state was not reset consistently

Expected

Compaction/reset code paths should preserve the same session invariants everywhere:

• hook contexts should expose a normalized deliverable messageProvider when one is actually known
• non-channel session keys should not manufacture fake providers
• post-compaction token/cost accounting should be refreshed from the compaction result, including zero-token outcomes

Actual

Different paths currently preserve different subsets of those invariants, so downstream systems must guess or degrade.

Scope

This is broader than the original single-field hook bug. It covers the coordinated compaction/reset invariant cluster now reported separately in:

• Bug: compaction/reset paths can break session invariants (messageProvider + token accounting) #69269
• Bug: session totalTokens not reset after compaction causes infinite safeguard loop #69286
• Bug: Session token count not reset after compaction #69287
• related cluster: Compaction failure leaves session in permanent failed state with no automatic recovery #69202