fix(auto-reply): preserve sessions after compaction failures (#70479)

Summary:
- The PR removes the auto-reply compaction-failure session reset hook, adds preserved-session recovery guidance for overflow/compaction failure paths, and updates focused tests, docs, and the changelog.
- Reproducibility: yes. at source level with high confidence. Current main routes both embedded overflow paylo ... resetSessionAfterCompactionFailure, and the PR body includes before/after terminal proof of those branches.

Automerge notes:
- PR branch already contained follow-up commit before automerge: fix(auto-reply): drop dead compaction reset hook
- PR branch already contained follow-up commit before automerge: fix(auto-reply): preserve sessions after compaction failures

Validation:
- ClawSweeper review passed for head 193d3c0fdd.
- Required merge gates passed before the squash merge.

Prepared head SHA: 193d3c0fdd
Review: https://github.com/openclaw/openclaw/pull/70479#issuecomment-4325128777

Co-authored-by: FullerStackDev <263060202+fuller-stack-dev@users.noreply.github.com>
Co-authored-by: vincentkoc <25068+vincentkoc@users.noreply.github.com>
Co-authored-by: clawsweeper[bot] <274271284+clawsweeper[bot]@users.noreply.github.com>
Approved-by: takhoffman
Co-authored-by: takhoffman <781889+takhoffman@users.noreply.github.com>

docs/reference/session-management-compaction.md

@@ -274,6 +274,11 @@ In the embedded Pi agent, auto-compaction triggers in two cases:
 number of tokens`, `input token count exceeds the maximum number of input
 tokens`, `input is too long for the model`, `ollama error: context length
 exceeded`, and similar provider-shaped variants) → compact → retry.
+   If overflow recovery still fails, OpenClaw surfaces explicit guidance to the
+   user and preserves the current session mapping instead of silently rotating
+   the session key to a fresh session id. The next step is operator-controlled:
+   retry the message, run `/compact`, or run `/new` when a fresh session is
+   preferred.
 2. **Threshold maintenance**: after a successful turn, when:
 
 `contextTokens > contextWindow - reserveTokens`