Freeze the language contracts for loops, calls and text templates

[ancongui]

Summary

Language milestone M0 (contract freeze). Lanes E, A and O can now build on frozen names; the compiler still refuses every new construct.

• Definitions accept forEach, callWorkflow, spec.callable, concat and join inside weave/v1alpha1; workflow.schema.json exports ForEachStep, CallWorkflowStep and CallableSpec. Existing documents and artifacts keep their canonical bytes and digests.
• Every compiler entry point reports WV-COMP-UNSUPPORTED_FEATURE at each use of forEach, callWorkflow, concat or join; callable compiles because it only declares an interface.
• Instance-key grammar (spec 3.2, C11) with parse, format and view functions, one regular expression and the API field types.
• Executables gain a frozen, always-empty features field; no IR version beyond weave/ir-v1alpha3 is emitted or accepted.
• Language manifest with studio: ready | pending marks, served through the platform API, the CLI, the SDK, the Studio host and weave schema export. Capabilities.step_kinds now lists all ten runnable kinds (it listed eight).
• Studio's schema-coverage.test.ts reads the manifest and compares only ready entries.
• Frozen scope_at signature and result models; the analysis lands with the loop compiler.
• Shared fixtures for Python and Studio, examples in examples/language/, and contract documentation.

Frozen names other lanes import

Contract	Name
Instance keys (C11)	firefly_weave.contracts.instance_keys: InstanceKey(node_id, indexes=(), segments=(), count=None), InvalidInstanceKey, node_of, split_instance, format_instance, InstanceView(node_id, instance_key, iteration), instance_view, INSTANCE_KEY_PATTERN (unanchored; Python uses re.fullmatch, ECMAScript and JSON Schema use ^(?:...)$), InstanceKeyText, InstanceKeyTextOrEmpty
Feature vocabulary (C5)	firefly_weave.contracts.language_features: LanguageFeature (text.concat, text.join, flow.forEach, flow.callWorkflow, ai.agent, ai.memory), LANGUAGE_FEATURES, ADVERTISED_FEATURES (empty in M0), KIND_FEATURES, OPERATOR_FEATURES, WORKFLOW_FIELD_FEATURES, DEFAULT_LOOP_MAX_ITEMS, MAX_LOOP_ITEMS, MAX_LOOP_DEPTH, MAX_RUN_ITERATIONS, MAX_CALL_DEPTH
Manifest (C5)	firefly_weave.contracts.language: LanguageManifest, ManifestStepKind, ManifestOperator, ManifestWorkflowField, ManifestBlock, ManifestLimits, Arity, language_manifest(features=ADVERTISED_FEATURES), supported_step_kinds(features=ADVERTISED_FEATURES), IR_VERSIONS, MANIFEST_VERSION = "weave/language-manifest-v1"
Manifest access	language.read = GET /api/v1/tenants/{tenant}/projects/{project}/language (catalog.read, bridged to Studio as family language); Studio host GET /studio/contracts/language; weave remote language; WeaveClient.language(); weave schema export writes language-manifest.schema.json
IR	firefly_weave.compiler.ir: ExecutableBase.features: list[LanguageFeature]; IR_VERSION_EXTENSIONS = "weave/ir-v1alpha4" (spec 3.1 name; defined, not accepted until M1)
Compiler	firefly_weave.compiler.language_support: COMPILED_FEATURES, UnsupportedUse, unsupported_uses(document); diagnostic WV-COMP-UNSUPPORTED_FEATURE
Scope	firefly_weave.compiler.scope: scope_at(document, path, *, catalog=None) -> ScopeResult, ScopeResult, ScopeEntry, ScopeSource
Definitions	ForEachStep, CallWorkflowStep, CallableSpec, CallerNames, WorkflowSpec.callable, OperatorName with concat and join
Shared fixtures	studio/tests/fixtures/language/instance-keys.json, text-conversion.json, manifest.json, generated by scripts/language_fixtures.py (--check for freshness)

Instance-key node IDs are the ASCII set @?[A-Za-z0-9][A-Za-z0-9_.:@-]* (step IDs and the synthetic @ IDs).

Not in this pull request

• Compilation, runtime and simulation of the new constructs (language milestones M1 to M9) and the agent manifest entry (Lane A).
• Shared fixtures for template segments (spec 4.5) arrive with M1, and scope_at cases (spec 14.3) with M3, when the code that produces them exists. Spec 14.5 lists them with M0, "extended by later milestones"; this pull request publishes the instance-key, text-conversion and manifest fixtures.

Follow-ups for later milestones

• M1: language_manifest(features) and Capabilities must add weave/ir-v1alpha4 to ir_versions once a feature is listed.
• M1: an unknown string in an artifact's features must classify as ir_unsupported, not a generic contract error (the field is typed with the six frozen values).
• M1: OperatorName now admits concat and join in provider-source mappings too; until they are evaluated there, such a mapping fails with a generic "Invalid request value".
• M3/M6: the artifact dependency walker in compiler/ir.py must descend into forEach bodies and handle callWorkflow references before those features compile.
• Each loop or call milestone shrinks EXPECTED in tests/unit/compiler/test_language_examples.py and re-checks notify-overdue and order-intake.

Local verification (macOS, head 7005566)

• make check: all 17 stages, All requested checks passed.
• scripts/language_fixtures.py --check and scripts/studio_schema_fixtures.py --check: exit 0.
• Studio: npm run check, npm run format:check, npm test (59 files, 657 tests passed), npm run build.
• Studio Playwright (npm run test:browser): 914 passed, 6 skipped. A first run under heavy machine load had two failures (connection.spec.ts:151, designer-forms.spec.ts:671) that passed in isolation and in the full rerun; this pull request changes no UI code.

CI scope

The Python suites run on Linux CI only (ci.yml uses ubuntu-latest; the macOS and Windows jobs in desktop.yml build the desktop app, not the Python suites) until S6-M0 lands the cross-platform tier. The Windows line-ending case for fixture freshness is covered by a unit test.

Test plan

• make check
• npm run check && npm run format:check && npm test && npm run build && npm run test:browser in studio/
• CI green on Linux; macOS and Windows for the Python suites after S6-M0