workspace tools: define model-friendly alias compatibility contract

[chubes4]

Problem

Live model/tool runs showed that agents use reasonable variants of workspace tool inputs, including mounted absolute paths and edit aliases such as search/replace and old/new.

PR #505 fixed the observed cases, but DMC should have an explicit compatibility contract and regression coverage so future model variants do not become one-off firefights.

Desired shape

Document and test the model-facing workspace tool compatibility layer:

• Absolute mounted paths under DATAMACHINE_WORKSPACE_PATH normalize to repo/path.
• Canonical edit inputs remain old_string/new_string.
• Supported edit aliases include search/replace and old/new.
• Unsupported aliases fail with actionable errors.
• Tool wrapper and lower WP Ability schemas remain consistent.

Layer boundary

DMC owns workspace tool input compatibility. WP Codebox may mount /workspace/<repo>, but DMC should normalize that shape generically. Data Machine should only extract/route tool calls; it should not know DMC workspace semantics.

Acceptance criteria

• Compatibility contract is documented near workspace tools or tests.
• Smoke coverage exercises tool-wrapper and ability-level validation.
• New aliases are intentionally added with tests instead of accidental broad argument matching.
• Sensitive or mutating required parameters are not filled from ambient context.

Related work

• Normalize mounted workspace paths in workspace tools #505
• Parse tag-style text tool calls data-machine#2436

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode (GPT-5.5)
• Used for: Drafting this issue from the model/tool-call compatibility fixes in PR Normalize mounted workspace paths in workspace tools #505.