fix: auto-extend compression ranges to prevent splitting tool_use/tool_result pairs (Issue #247)

[ranxianglei]

Summary

Fixes #247 — compression ranges can split tool_use/tool_result pairs, creating orphaned references that cause provider API rejection.

Problem: When a compression range includes a tool_use (assistant) but not its tool_result (user), or vice versa, the pruned output has an orphaned tool_use_id/tool_result_id reference → provider API rejects: "tool_result block does not have a corresponding tool_use".

Fix: adjustBoundariesForToolPairs in lib/compress/search.ts auto-extends range boundaries to include paired messages:

• Collects all non-compress tool callIDs in the range
• Forward scan (≤20 msgs): extends endIdx to include tool_results matching in-range callIDs
• Backward scan (≤20 msgs): extends startIdx to include tool_uses matching in-range callIDs
• Stops at first gap after finding a match

Oracle Review Fixes (commit 2)

Oracle review found tier misclassification risk: block anchors are compress tool_use messages (have callIDs), so forward scan would flip endReference.kind from "compressed-block" to "message", corrupting tier detection in applyCompressionState (T2 → T1).

Two fixes:

1. Exclude compress tool from scan: compress is always force-protected, its pairs survive intact regardless — no need to adjust for them
2. Only extend MESSAGE boundaries: block boundaries (bN) are never adjusted, preserving tier metadata

Test Coverage (11 tests)

Test	Covers
forward extension	tool_use at endIdx, result after
backward extension	result at startIdx, use before
pair inside range	no extension
no tool calls	no extension
multiple results	one use, multiple result msgs
parallel calls	one message, multiple callIDs
gap tolerance	non-tool msg between use and result
flows to resolveSelection	toolIds include paired messages
kind change (message→message)	backward extension on message boundary
block boundary kind preserved	T2 distillation b1→b1, compress excluded
compress excluded from scan	message boundary, compress calls don't trigger extension

CI

All 5 checks pass: pr-validation ✓, test (22) ✓, test (24) ✓, build ✓, e2e ✓
949 tests (0 failures).