(fix) page large-block decompress output with offset/limit so one recovery can't flood or get silently trimmed

[ranxianglei]

Fixes #112.

Problem
decompress (and /acp decompress) expands ALL shadowed seqs of a block into one uncapped tool result. For a large block (say 200K tokens) the recovered text either floods the model's context or — more usually — gets silently truncated by the host tool-result pruner (dsh-compaction-tool-result-pruner, tiers 8192/4096/1024): the tail of the recovered content is gone while the model believes it holds the whole block. That is precisely the failure mode decompress exists to undo.

Cause
handleDecompress (src/tools.ts) joins expandShadowedSeqs(session, block.blockId) into a single string; the tool schema only exposes blockId, so there is no way to page through.

Fix

• sliceDecompressPage(expanded, offset, limit) + DEFAULT_DECOMPRESS_PAGE = 100 (src/region.ts): pure paging helper shared by the tool and the command. Clamps offset >= 0, limit >= 1; empty-text seqs still occupy slots so paging stays stable across calls.
• decompress tool: optional integer offset / limit params. Results end with [messages X..Y of Z] plus an explicit continue hint (decompress({ blockId: "<id>", offset: N })) when more remains; an offset past the end returns guidance instead of an error.
• /acp decompress <blockId> [offset] [limit]: same paging and footer (8-char prefix form); non-numeric args are rejected.
• Default prompt copy (src/prompts.ts) + tool descriptions updated to mention paging; README.md / README.en.md tool table synced.

Small blocks behave as before (a <= 100 message block returns whole, plus the new [messages X..Y of Z] footer).

Verification

• New regression tests:
  • tests/tools.test.ts "M3: decompress pages a large block by default and walks it with offset" — compresses 120 messages, asserts page 1 = [messages 1..100 of 120] + continue hint, walks to the final page via offset, and checks past-end guidance.
  • tests/tools.test.ts "M3: decompress honors an explicit limit and clamps a negative offset".
  • tests/commands.test.ts "M4: /acp decompress pages with [offset] [limit] args and rejects bad numbers".
• npm run typecheck clean; npm test 211 pass / 0 fail (208 baseline + 3 new); npm run build clean (dist committed per AGENTS.md §4).

Built against main @ 6348af8 (v0.2.20).

[ranxianglei]

我来协助看一下这个问题,请分析并回复处理结果。