feat(context): config hot-reload via ContextPipeline middleware

[yishuiliunian]

Summary

• Wire ContextPipeline (previously test-only) into the agent loop as a pre-LLM middleware pipeline
• Add ConfigRefreshMiddleware that detects mid-session file changes (memory, instructions, settings) via mtime polling and injects diffs as system-reminder user messages
• System prompt is never modified — Anthropic prefix cache is preserved

Changes

New files (loopal-context):

• middleware/file_snapshot.rs — FileSnapshot with stat-then-read TOCTOU safety, ordered line diff preserving duplicates, formatted change summaries
• middleware/config_refresh.rs — ConfigRefreshMiddleware impl with Mutex<Vec<FileSnapshot>> for interior mutability
• tests/suite/file_snapshot_test.rs — 15 tests (diff, format, snapshot lifecycle, unicode, sequential changes)
• tests/suite/config_refresh_test.rs — 5 tests (no-change, injection, dedup, cache safety, multi-file)

New files (loopal-runtime):

• agent_loop/context_pipeline.rs — bridge method run_context_pipeline() (non-fatal, errors logged and swallowed)
• agent_loop/pipeline_setup.rs — build_context_pipeline() watching 9 file paths (global+project memory/instructions/settings)
• agent_loop/params.rs — extracted AgentConfig, AgentLoopParams, AgentDeps, etc. from mod.rs
• agent_loop/turn_tool_phase.rs — extracted tool execution phase from turn_exec.rs

Modified files:

• middleware/mod.rs — export new modules
• runner.rs — added pipeline: ContextPipeline field
• turn_exec.rs — call run_context_pipeline() before LLM, delegate tool phase
• mod.rs — build pipeline in agent_loop(), re-export from params.rs

Watched paths (9 total)

File	Label
~/.loopal/memory/MEMORY.md	Global Memory
.loopal/memory/MEMORY.md	Project Memory
~/.loopal/LOOPAL.md	Global Instructions
~/.loopal/LOOPAL.local.md	Global Local Instructions
LOOPAL.md	Project Instructions
.loopal/LOOPAL.local.md	Local Instructions
~/.loopal/settings.json	Global Settings
.loopal/settings.json	Project Settings
.loopal/settings.local.json	Local Settings

Test plan

• bazel build //... --config=clippy — zero warnings
• bazel test //crates/loopal-context:loopal-context_test — 20 tests pass (including new)
• bazel test //crates/loopal-runtime:loopal-runtime_test — all pass
• CI passes