chore(openspec): drop 9 superseded proposals + 11 stub archive files

Drop 9 batch proposals that are superseded by the boocode-lift-analysis
(boocontext-audit, conductor upgrades, self-healing/verify-gate skills):
add-3tier-memory, import-llm-evaluator, import-pregel-engine, plugin-platform,
conductor-evolution, code-intelligence-upgrade, dev-workflow, ui-overhaul,
agent-reliability.

Delete 11 stub archive files (49-66B each, 'Status: Shipped. Archived.' only)
that provide zero documentation value over the existing CHANGELOG.md + git tags.

openspec/changes/archived/2026-06-07-hybrid-workflow-engine/specs/variable-substitution/spec.md

@@ -0,0 +1,57 @@
+## ADDED Requirements
+
+### Requirement: Node output references
+Prompts and commands SHALL support `$nodeId.output` to reference the output text of an upstream node, and `$nodeId.output.field` to reference a specific field from a structured output.
+
+#### Scenario: Output reference substitution
+- **WHEN** a prompt contains `$analysis.output`
+- **THEN** it SHALL be replaced with the full output text of the node with id `analysis`
+
+#### Scenario: Field reference with structured output
+- **WHEN** a prompt contains `$analysis.output.summary` and the upstream node declared `output_format: { type: "object", properties: { summary: ... } }`
+- **THEN** it SHALL be replaced with the value of the `summary` field from the parsed JSON output
+
+#### Scenario: Missing node reference
+- **WHEN** a prompt references `$nonexistent.output`
+- **THEN** the reference SHALL resolve to an empty string with a warning
+
+#### Scenario: Missing field on schemaless node
+- **WHEN** a prompt references `$node.output.field` and the upstream node has no `output_format` and its output is not valid JSON
+- **THEN** the consuming node SHALL fail with an error
+
+#### Scenario: Strict field access for declared schemas
+- **WHEN** a prompt references `$node.output.field` and the upstream node's `output_format` declares properties but `field` is not among them
+- **THEN** the consuming node SHALL fail with a field-not-found error
+
+### Requirement: Built-in variables
+The engine SHALL support `$ARGUMENTS`, `$ARTIFACTS_DIR`, `$WORKFLOW_ID`, `$BASE_BRANCH`, `$DOCS_DIR`.
+
+#### Scenario: $ARGUMENTS substitution
+- **WHEN** a prompt contains `$ARGUMENTS`
+- **THEN** it SHALL be replaced with the full user message/arguments string
+
+#### Scenario: $ARTIFACTS_DIR substitution
+- **WHEN** a prompt contains `$ARTIFACTS_DIR`
+- **THEN** it SHALL be replaced with the path to the run's artifact directory
+
+#### Scenario: $WORKFLOW_ID substitution
+- **WHEN** a prompt contains `$WORKFLOW_ID`
+- **THEN** it SHALL be replaced with the workflow run ID
+
+### Requirement: Loop-specific variables
+Loop nodes SHALL support `$LOOP_USER_INPUT` (from approve at interactive gates) and `$LOOP_PREV_OUTPUT` (output of the previous iteration).
+
+#### Scenario: $LOOP_PREV_OUTPUT on first iteration
+- **WHEN** a loop node is on its first iteration
+- **THEN** `$LOOP_PREV_OUTPUT` SHALL resolve to an empty string
+
+#### Scenario: $LOOP_PREV_OUTPUT on subsequent iterations
+- **WHEN** a loop node is on iteration 2+
+- **THEN** `$LOOP_PREV_OUTPUT` SHALL contain the cleaned output of the previous iteration
+
+### Requirement: Approval-specific variables
+Approval nodes SHALL support `$REJECTION_REASON`.
+
+#### Scenario: $REJECTION_REASON in on_reject prompt
+- **WHEN** an approval node is rejected with a reason
+- **THEN** `$REJECTION_REASON` SHALL contain the reviewer's feedback text