fix(parser): sanitize lone UTF-16 surrogates before JSONL parsing (fixes #85)

[delexw]

Problem

JSONL files written by Claude Code before v2.1.132 may contain lone UTF-16 surrogate code units (e.g. \uD83D without a matching \uDCxx low surrogate) inside tool_result content block strings. This happens when Claude Code's tool-error truncation logic split a multi-byte emoji at an offset boundary.

serde_json rejects lone surrogates per RFC 8259, causing parse_entry to silently discard any JSONL line that contains one.

Fix

Add a sanitize_lone_surrogates() pre-pass that runs on the raw JSONL text before handing it to serde_json::from_str. It scans for \uXXXX escape sequences in the surrogate range (U+D800–U+DFFF) and:

• Lone high surrogate (\uD8xx not followed by \uDCxx–\uDFxx): replaced with �
• Lone low surrogate (\uDCxx–\uDFxx not preceded by a valid high surrogate): replaced with �
• Valid surrogate pair (\uD8xx\uDCxx): preserved as-is

Allocation is deferred: strings containing no surrogates return Cow::Borrowed with zero copies.

parse_entry is updated to convert the raw bytes to &str first (failing fast on non-UTF-8, which serde_json::from_slice would also reject) and then apply the sanitizer before deserialization.

Files Changed

• src-tauri/src/parser/entry.rs — added hex4_to_u16, sanitize_lone_surrogates, updated parse_entry

Tests Added

10 new tests in parser::entry::tests:

Test	Verifies
sanitize_lone_surrogates_no_surrogates_returns_borrowed	zero-copy fast path
sanitize_lone_high_surrogate_replaced_with_fffd	lone \uD83D → �
sanitize_lone_low_surrogate_replaced_with_fffd	lone \uDC36 → �
sanitize_valid_surrogate_pair_unchanged	valid pair preserved
sanitize_multiple_lone_surrogates_all_replaced	two lone surrogates, both replaced
sanitize_high_surrogate_at_end_of_string_replaced	lone surrogate at string boundary
parse_entry_with_lone_high_surrogate_succeeds	end-to-end: line parses instead of returning None
parse_entry_with_lone_low_surrogate_succeeds	end-to-end: lone low surrogate
parse_entry_with_valid_surrogate_pair_succeeds	end-to-end: valid pair still parses

All 390 Rust tests and 352 frontend tests pass.

Fixes #85