feat(core): add normal resize recovery

[zikolach]

Summary

• add shared NormalResizeRecoveryProvider and positive NormalResizeRecoveryContext APIs plus opt-in TUIOptions.normalResizeRecovery
• fail before terminal startup when recovery is combined with alternate-screen mode or scrollback-clearing resize policy
• render the retained frame first, reserve its physical footprint (including an empty-frame cursor anchor), and invoke the synchronous text-only provider with a strict current-geometry row budget
• sanitize recovery lines without retaining provider text in the content-bearing sanitization sample; reject oversized output before publication
• serialize viewport clear, retained-control cleanup, recovery, live-frame controls, cursor placement, and autowrap restoration in one TUI-owned write
• keep recovery outside previousFrame, preserve live-frame-relative cursor/mouse/layout state, and place later appends in recovered -> appended -> live frame order
• discard stale candidates, retry latest coalesced geometry through existing fair Render work, and discard candidates when stop wins before publication
• add redacted completed/discarded/provider/budget/write recovery diagnostics
• add shared JVM/Scala Native virtual-terminal coverage, JVM PTY ordering/restoration coverage, docs, smoke instructions, changelog, and completed OpenSpec artifacts

Safety and scope

The first version returns ordinary Vector[String] lines rather than ComponentRender, so recovery cannot acquire component, cursor, image, cleanup, or raw-terminal authority. Siglyph retains no transcript and cannot inspect emulator scrollback; applications remain responsible for current-width semantic tail selection and terminal-dependent deduplication.

No terminal backend API or third-party runtime dependency changed.

Validation

• focused shared recovery, append, TUI concurrency, diagnostics, virtual-terminal, TUI, and JVM PTY suites — passed
• mill core.test — passed
• SIGLYPH_NATIVE_CLANG=/usr/local/opt/llvm/bin/clang SIGLYPH_NATIVE_CLANGPP=/usr/local/opt/llvm/bin/clang++ mill coreNative.test — 38 test classes passed
• SIGLYPH_NATIVE_CLANG=/usr/local/opt/llvm/bin/clang SIGLYPH_NATIVE_CLANGPP=/usr/local/opt/llvm/bin/clang++ mill __.compile — passed
• mill scalafmtCheck — passed
• mill scalafixCheck — passed
• scripts/test-terminal-pty.sh — passed on macOS
• openspec validate --all --strict — 15 passed, 0 failed
• git diff --check
• OpenSpec implementation tasks — 39/39 complete

Manual Kitty/iTerm2/conventional-emulator persistence checks are documented but were not available in this non-emulator test environment. PTY coverage verifies byte ordering, CSI 3 J absence, synchronized output, append chronology, and restoration without claiming emulator persistence.

Closes #56

[zikolach]

AI-assisted comprehensive review (Pi coding agent). I reviewed the OpenSpec proposal/design/deltas/tasks, public API, owner scheduling, stale/stop behavior, recovery/live publication, append chronology, cursor/mouse/control ownership, diagnostics/redaction, JVM/Native scope, PTY coverage, and documentation.

I found two blocking contract/design issues and one documentation mismatch in the inline comments. The implementation is otherwise unusually thorough: the text-only authority boundary, one-write publication, live-only differential baseline, fail-fast validation, diagnostics, and test coverage are well structured.

Validation performed:

• mill core.test: passed (135 test classes)
• mill scalafmtCheck scalafixCheck: passed
• openspec validate --all --strict: 15/15 passed
• git diff --check: passed
• focused local same-geometry probe: failed as described inline
• GitHub CI: both JVM/package and macOS terminal-conformance jobs pass

Review readiness: needs design clarification/fixes before merge, primarily so an application can actually select only the invalidated durable tail rather than necessarily over-replaying on viewport growth.