[jcombs-pointblue]

A driver's trace size limit (`DirXML-TraceSizeLimit`) is driver configuration, so the tree now records it.

What changes

• `import-live`, a Designer project and a Designer export read it into `driver.xml` as `trace-size-limit`. It is absent when the driver inherits the driver set's (Designer's `inherit="true"` / `IdmParameter:InheritTraceSize`). Writing a Designer project or export carries it back.
• New driver: created with the tree's limit.
• Existing driver: the vault keeps its own value unless `vault.deploy --trace-size-limit` is given. Without the flag, the plan notes the difference and the run ends "nothing to deploy — the plan leaves the differences above as the notes say".
• No restart: the engine reads trace settings live.
• Never drift: the production known-state check and capture ignore it.
• Older trees: a tree that doesn't record a limit asks for nothing, so they diff as before.
• Editing and overrides: `driver.set --key trace-size-limit` (whole numbers only; `--clear` stops recording it), the override key `drivers/.trace-size-limit`, and `vault.compare-envs` values.
• Trace level and file: these stay operational (`driver.trace`). The decision is recorded in vault-deploy.md, Decisions 6.

Checked

• Full suite: 1048 tests, 0 failures. New tests cover plan (new / existing / flag / no restart), diff, overrides, round trip, and the LDIF, export and project readers.
• On edir3, with nothing written:
  • `import-live` records each driver's limit (the AD driver: 200000).
  • The current `tree-edir3`, which records no limits, still diffs clean.
  • In a scratch copy with the AD limit set to 100000, `vault.diff` shows `~ trace-size-limit: 200000 -> 100000`.
  • The dry-run without the flag plans 0 steps and notes the difference.
  • The dry-run with `--trace-size-limit` plans one `modify DirXML-TraceSizeLimit = 100000 (was 200000)` and 0 restarts.

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