feat: decompress tool range mode (startId/endId) — issue #14

[ranxianglei]

Summary

Adds optional startId/endId params to the decompress tool schema as an alternative to blockId. Range mode batch-restores every active block whose effectiveMessageIds overlaps the resolved message range in one call — eliminating the acp_status → decompress-per-block loop.

Mirrors Gitea PR #15.

Changes

• lib/compress/decompress.ts — schema gains optional startId/endId; handler refactored into resolveTargets dispatcher → resolveSingleBlockTarget (unchanged) | resolveRangeTarget (new). Shared tail handles N targets (toFile gather, deactivate loop, pluralized report).
• lib/compress/decompress-logic.ts — new exported findActiveBlocksOverlappingMessages(messagesState, messageIdSet). Pure, O(blocks × effectiveIds), dedupes via Map, returns sorted by blockId.
• tests/decompress-logic.test.ts — 11 new tests covering empty set, no blocks, overlap match, inactive skip, partial overlap, multi-block sort, dedupe, disjoint, undefined effectiveIds, nested child-only, nested ancestor+child.
• devlog/2026-07-07_decompress-range-mode/ — REQ.md, DESIGN.md, WORKLOG.md.

Design highlights

• Reuses compress/search.ts for boundary resolution — inherits Bug 34 (auto-swap reversed boundaries), OOB clamping, and recovery hints for free.
• Nested correctness without a parent-chain walk: a child block's effectiveMessageIds ⊇ consumed ancestor's effective IDs, so both are always matched when the range overlaps. Proof in devlog/2026-07-07_decompress-range-mode/DESIGN.md.
• Backward compatible: blockId path byte-identical to before. New fields are optional; blockId XOR (startId AND endId) enforced at handler level with clear errors.

Schema

decompress({
  blockId?: string,      // "b0" — use this OR startId+endId
  startId?:  string,     // "m00150" — range start
  endId?:    string,     // "m00200" — range end
  toFile?:   string,     // optional, writes to file instead of inflating context
})

Edge cases handled

• blockId + startId/endId mixed → mutual-exclusivity error
• Only one of startId/endId → error
• Range with no overlapping active blocks → error pointing to acp_status
• Reversed boundaries → auto-swapped (Bug 34 fix)
• Partial overlap → whole block decompressed (atomic)
• Nested blocks → both ancestor and child restored

Verification

• npm run typecheck — PASS
• npm run build — PASS (dist/index.js 357 KB)
• bun test tests/ — 586 pass, 1 pre-existing fail (Bun limitation in prompts.test.ts:53 — nested test() unsupported; verified on master via stash/pop)

Follow-ups

• Dual-agent code review per AGENTS.md §5.3
• Prompt update to advertise range mode (separate PR, pairs with feat: rewrite compression format prompt with KEEP/DROP/PRIORITY taxonomy (issue #13) #72)