Add resilient multi-account orchestration helpers (#22)

* Add SDK orchestration helpers for resilient multi-account collection

- collect_latest_rates_for_accounts_with_retries(): exponential-backoff
  retries around collect_latest_rates_for_accounts(), retrying only
  Mt5TradingError/Mt5RuntimeError and re-raising on exhaustion.
- resolve_account_spec()/resolve_account_specs() and
  substitute_env_placeholders(): merge explicit overrides over AccountSpec
  fields and expand ${ENV_VAR} placeholders, raising ValueError on missing
  variables.
- ThrottledHistoryUpdater: monotonic-clock throttled wrapper around
  update_history() with should_update()/update() and opt-in suppress_errors.
- load_rate_series_by_granularity(): rate-series loader keyed by
  (symbol | None, granularity_name).
- Export new APIs, add unit tests (100% coverage), and document in README
  and docs/api.

* chore: bump version from 0.5.1 to 0.5.3 (#24)

Co-authored-by: Cursor Agent <cursoragent@cursor.com>
Co-authored-by: Daichi Narushima <dceoy@users.noreply.github.com>

* fix: resolve leftover merge conflict markers in version files

Co-authored-by: Daichi Narushima <dceoy@users.noreply.github.com>

* fix: address PR review feedback on SDK orchestration helpers

- Use single-pass env substitution to avoid TOCTOU KeyError
- Apply backoff_base to all retry delays (backoff_base ** (attempt + 1))
- Preserve integer logins in resolve_account_spec; hide login in repr
- Fix docs examples (env ordering, while True loop, backoff comment)
- Parametrize suppress_errors tests for MT5 and SQLite errors

Co-authored-by: Daichi Narushima <dceoy@users.noreply.github.com>

---------

Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: Cursor Agent <cursoragent@cursor.com>
Co-authored-by: Daichi Narushima <dceoy@users.noreply.github.com>

README.md

@@ -136,7 +136,10 @@ update_history_with_config(
 - **Rate view resolution**: use `resolve_rate_view_name()` / `resolve_rate_view_names()` to map symbols and granularities to existing SQLite compatibility views without creating databases. Both accept `None` (or a missing path) and return deterministic default names unless `require_existing=True`.
 - **Rate view loading**: use `load_rate_data()` / `load_rate_data_from_connection()` to load a SQLite rate table or view into a `DatetimeIndex` DataFrame.
 - **Multi-series rate loading**: use `build_rate_targets()` to build neutral `RateTarget(symbol, timeframe)` pairs, `resolve_rate_tables()` to map them to table/view names (pass `require_existing=True` for strict resolution), and `load_rate_series_from_sqlite()` to load them into a mapping keyed by `(symbol, integer timeframe)`. The loader requires existing managed views unless `explicit_tables` is supplied, and rejects duplicate `(symbol, timeframe)` targets.
-- **Multi-account latest rates**: use `collect_latest_rates_for_accounts()` with `AccountSpec` to read the latest bars for several account groups, merged into a `(symbol, integer timeframe)` mapping.
+- **Multi-account latest rates**: use `collect_latest_rates_for_accounts()` with `AccountSpec` to read the latest bars for several account groups, merged into a `(symbol, integer timeframe)` mapping. For long-running pollers, `collect_latest_rates_for_accounts_with_retries()` adds bounded exponential backoff that retries only `pdmt5.Mt5TradingError` / `pdmt5.Mt5RuntimeError` and re-raises once `retry_count` is exhausted.
+- **Credential resolution**: use `resolve_account_spec()` / `resolve_account_specs()` to merge explicit override values over `AccountSpec` fields and expand `${ENV_VAR}` placeholders (via `substitute_env_placeholders()`), raising `ValueError` for missing variables. This keeps secrets out of plan/config files without coupling to any strategy code.
+- **Throttled history updates**: use `ThrottledHistoryUpdater` to wrap `update_history()` with a minimum `interval_seconds` between successful runs (monotonic clock). Call `should_update()` / `update(client, symbols)` from an application loop; errors propagate by default, or pass `suppress_errors=True` to swallow recoverable `Mt5*Error`/`sqlite3.Error` and let the caller decide logging.
+- **Granularity-keyed rate loading**: `load_rate_series_by_granularity()` builds targets with `build_rate_targets()`, loads them with `load_rate_series_from_sqlite()`, and returns a mapping keyed by `(symbol | None, granularity_name)` such as `("EURUSD", "M1")` to reduce downstream boilerplate.
 - **MT5 session helper**: use the `mt5_session()` context manager to attach to (or, when `Mt5Config.path` is set, launch) an MT5 terminal, log in, and yield a connected `Mt5CliClient` that shuts down on exit.
 - **SQLite export helpers**: use `export_dataframe_to_sqlite()` for append mode, optional index export, and post-write deduplication by key columns.
 - **Recent ticks and margins**: `recent_ticks()` and `minimum_margins()` SDK helpers (and matching CLI commands) cover common downstream read-only queries.