/**
 * Tool registry, model presentation modes, and pre/guard/around/post/result
 * execution pipeline.
 * @module @deepseek-ai/dsh-tools
 */

import { Context, Service } from 'cordis'
import z from 'schemastery'
import { scopeOf, scopeTarget } from '@deepseek-ai/dsh-scope'
import type { ScopeKey, Scoped } from '@deepseek-ai/dsh-scope'
import type { CallId, ContentBlock, ToolSchema } from '@deepseek-ai/dsh-llm'
import { assertNever, deepFreeze, HarnessError } from '@deepseek-ai/dsh-llm'
import type { Agent, HookContext } from '@deepseek-ai/dsh-agent'
import { snapshotJsonValue } from '@deepseek-ai/dsh-session'
import type { ToolProviderResult } from '@deepseek-ai/dsh-system-prompt'
import type { CodeRuntime } from '@deepseek-ai/dsh-code-runtime'
// Type-only: makes `ctx.get('approval')` resolve to the ApprovalService
// augmentation. The seam stays optional at runtime — see `serviceAsk`.
import type {} from '@deepseek-ai/dsh-user-approval'
import type { ToolCallView, ToolResultView } from './presentation.ts'
import { createRunCodeTool, RUN_CODE_NAME, SDK_SECTION_ORDER } from './code-mode.ts'
import { renderToolsSdk } from './ts-types.ts'

export {
  defineTool,
  schemaSpecToJsonSchema,
  validateArgs,
  ToolArgsError,
  type SchemaSpec,
  type SchemaProp,
  type SchemaType,
  type InferArgs,
  type DefineToolOptions,
  type JsonSchemaObject,
} from './schema.ts'

export {
  assertSupportedOutputSchema,
  validateStructuredValue,
  OutputSchemaError,
  type StructuredOutputSchema,
  type StructuredSchemaNode,
  type StructuredSchemaType,
  type StructuredScalar,
} from './json-schema.ts'

export { CodeRunFailedError, RUN_CODE_NAME } from './code-mode.ts'
export { jsonSchemaToTs, renderToolsSdk } from './ts-types.ts'

// The render-intent vocabulary a tool declares via `presentCall`/`presentResult`
// lives in its own UI-facing module; re-export it so `@deepseek-ai/dsh-tools`
// stays the single public surface for consumers (producers + the ACP bridge).
export type {
  ToolCallKind,
  FileLocation,
  FileDiff,
  ToolCallView,
  GenericCallView,
  TerminalCallView,
  DiffCallView,
  ToolResultView,
  GenericResultView,
  TerminalResultView,
  DiffResultView,
} from './presentation.ts'

declare module 'cordis' {
  interface Context {
    tools: ToolRegistry
  }

  interface Events {
    /**
     * Allow, deny, or ask before dispatch. `next()` delegates to allow; missing
     * approval support turns `ask` into denial.
     * Scope-filtered dispatch (`@deepseek-ai/dsh-scope`): agent-scoped listeners receive only that agent's calls.
     * @param exec - the pending call (name, parsed arguments, caller agent).
     * @mode waterfall
     */
    'tools/pre-execute'(this: Scoped<ToolRegistry>, exec: ToolExecution, next: () => Promise<PreToolDecision>): Promise<PreToolDecision>
    /**
     * Around-dispatch waterfall for timeout, retry, or metrics. `next()` returns
     * a normalized result; wrappers may change only `exec.signal`, while call
     * identity remains immutable.
     * Scope-filtered dispatch (`@deepseek-ai/dsh-scope`): agent-scoped listeners receive only that agent's calls.
     * @param exec - the allowed call about to dispatch (name, parsed arguments, caller agent, signal).
     * @mode waterfall
     */
    'tools/execute'(this: Scoped<ToolRegistry>, exec: ToolExecution, next: () => Promise<ToolExecutionResult>): Promise<ToolExecutionResult>
    /**
     * Accept, replace, enrich, or block a normalized dispatch result. `next()`
     * accepts it unchanged; thrown tools still reach this seam as errors.
     * Scope-filtered dispatch (`@deepseek-ai/dsh-scope`): agent-scoped listeners receive only that agent's calls.
     * @param exec - the call that just ran (name, parsed arguments, caller agent).
     * @param result - the dispatch outcome a listener may accept, replace, or block.
     * @mode waterfall
     */
    'tools/post-execute'(this: Scoped<ToolRegistry>, exec: ToolExecution, result: Readonly<ToolExecutionResult>, next: () => Promise<PostToolDecision>): Promise<PostToolDecision>
    /**
     * Observe the frozen, lossless-JSON final outcome. Listener failures are contained.
     * Scope-filtered dispatch (`@deepseek-ai/dsh-scope`): keyed by `exec.agent`.
     * @param exec - the execution object that traversed the pipeline.
     * @param result - a deep-frozen snapshot of the final returned result.
     * @mode emit
     */
    'tools/result'(this: Scoped<ToolRegistry>, exec: Readonly<ToolExecution>, result: Readonly<ToolExecutionResult>): undefined
    /**
     * A tool was registered or unregistered, or a scoped restriction changed
     * (the available tool set changed — possibly for one scope only). An
     * UNFILTERED registry-subject notification, deliberately not scope-filtered
     * dispatch: a global change concerns every agent's next assembly, so a
     * scoped listener subscribing here sees every change, not just its own
     * scope's.
     * @mode emit
     */
    'tools/change'(): void
  }
}

/** Tool output, optionally with lossless-JSON presentation metadata persisted for replay. */
export type ToolExecuteReturn = ContentBlock[] | { content: ContentBlock[]; meta?: unknown }

/** A registered tool: its schema plus the execution function. */
export interface ToolDefinition extends ToolSchema {
  execute(args: unknown, exec: ToolRunContext): Promise<ToolExecuteReturn>
  /**
   * Cooperative tool-call timeout budget in milliseconds. Omit for no deadline.
   * Enforced by `@deepseek-ai/dsh-timeout-policy` (a `tools/execute` wrapper); it
   * is NEVER sent to the model — `schemas()` whitelists only name/description/
   * parameters. Declaring it asserts this tool forwards `exec.signal` to a
   * cooperative implementation that can reach quiescence when the signal aborts.
   */
  timeoutMs?: number
  /**
   * Pure synchronous classifier for overlap with sibling tool calls. Only
   * `true` opts in; omission, exceptions, non-`true` returns, and invalid
   * `defineTool` arguments are exclusive. This metadata is never model-visible.
   *
   * Opted-in executions must not mutate parent-owned state. Shared state must
   * tolerate concurrent dispatch; recorder races are permitted only when they
   * commute or fail closed. See the
   * [parallel-tool-call Agent Note](../../../../.agents/notes/implemented/feature/2026-07-10-parallel-tool-call-execution.md)
   * for the full contract.
   * @param args - parsed arguments; `defineTool` validates before calling.
   * @returns Whether this call may join a parallel group.
   */
  isConcurrencySafe?(args: unknown): boolean
  /**
   * Optional: how to present the PENDING state of one call in a UI, derived from
   * the call's `args` (parsed arguments, `unknown` — the tool validates/narrows
   * its own input). Returns a {@link ToolCallView} (a `card`-tagged render intent),
   * or `undefined` (or omit the method) to fall back to a generic presentation
   * (title = tool name, raw args as input). Pure and side-effect-free: a UI may
   * call it during live streaming AND a session-log replay, so it must depend
   * only on `args`.
   */
  presentCall?(args: unknown): ToolCallView | undefined
  /**
   * Optional: how to present the COMPLETED state, given the same `args` and the
   * `result` (`execute`'s content + whether it errored). Returns a
   * {@link ToolResultView}, or `undefined` (or omit the method) to keep the
   * pending title and render the raw result content. Pure and side-effect-free
   * for the same replay reason.
   */
  presentResult?(args: unknown, result: ToolResult): ToolResultView | undefined
}

/** The completed outcome handed to {@link ToolDefinition.presentResult}. */
export interface ToolResult {
  /** The model-facing content `execute` returned (or the error text on failure). */
  content: ContentBlock[]
  /** Whether the call failed. */
  isError: boolean
  /**
   * The tool-private presentation payload the tool attached from `execute` (via
   * the object return form), threaded verbatim from the `tool/result` event.
   * Opaque (`unknown`); the tool narrows it back to its own shape. Absent when
   * the tool attached none.
   */
  meta?: unknown
}

declare const toolExecutionTokenBrand: unique symbol

/** Opaque call identity that permits correlation without exposing mutable execution state. */
export type ToolExecutionToken = symbol & { readonly [toolExecutionTokenBrand]: true }

/**
 * Caller-supplied description of one tool call. {@link ToolRegistry.execute}
 * adds the registry-owned token to form a pipeline {@link ToolExecution};
 * callers do not choose that token.
 */
export interface ToolExecutionInput {
  readonly callId: CallId
  readonly name: string
  /** Losslessly JSON-serializable parsed arguments (tools validate their own schema). */
  readonly arguments: unknown
  /** The agent on whose behalf the call runs (set by the agent loop). */
  readonly agent?: Agent
  /**
   * Opaque token of the enclosing transport execution, when one exists. Code
   * Mode sets this on SDK sub-dispatches so commit-style observers can wait for
   * the outer `run_code` outcome without receiving its live mutable execution.
   */
  readonly parent?: ToolExecutionToken
  signal?: AbortSignal
}

/**
 * Scheduling mode for one pending call. `parallel` may overlap with siblings;
 * `exclusive` runs alone and forms an ordering barrier.
 */
export type ToolExecutionMode =
  | { kind: 'parallel' }
  | { kind: 'exclusive' }

/**
 * One pending tool call inside the registry pipeline. Parsed arguments cross
 * one lossless-JSON materialization boundary before policy and are deep-frozen;
 * call identity and the registry-assigned {@link token} are readonly. An
 * around-dispatch wrapper may set, replace, or remove `signal`. The registry
 * freezes the complete object before `tools/result` observers run.
 */
export interface ToolExecution extends ToolExecutionInput {
  /** Registry-assigned identity shared with nested calls only as their opaque `parent` token. */
  readonly token: ToolExecutionToken
}

/**
 * Runtime context handed to a tool implementation after the registry has
 * accepted a {@link ToolExecution}. A composite tool uses
 * {@link deferContext} to ferry context produced by nested dispatches back to
 * the outer result; the loop appends it only after the outer `tool/result`.
 */
export interface ToolRunContext extends ToolExecution {
  /**
   * Defer one nested-dispatch context until this tool's final result reaches
   * the agent loop. Contexts retain their individual source and metadata and
   * are emitted in call order.
   */
  deferContext(context: HookContext): void
}

/**
 * Scheduler-only result after ordered pre-execute and guards. A `post-result`
 * still receives post-execute; a `final-result` bypasses it.
 * @internal
 */
export type ScheduledToolPreparation =
  | { kind: 'dispatch'; exec: ToolRunContext }
  | { kind: 'post-result'; exec: ToolRunContext; result: ToolExecutionResult }
  | { kind: 'final-result'; exec: ToolRunContext; result: ToolExecutionResult }

/**
 * Scheduler-only dispatch result. A `post-result` still receives post-execute;
 * a `final-result` already matches {@link ToolRegistry.execute} failure semantics.
 * @internal
 */
export type ScheduledToolDispatch =
  | { kind: 'post-result'; result: ToolExecutionResult }
  | { kind: 'final-result'; result: ToolExecutionResult }

/**
 * Symbol-keyed scheduler view that keeps pre/post policy ordered while
 * overlapping dispatch. Ordinary callers use {@link ToolRegistry.execute};
 * this is not a plugin seam.
 * @internal
 */
export interface ToolRegistryScheduler {
  /** Materialize input, run the ordered pre-execute/guard gate, and decide what stage follows. */
  prepare(exec: ToolExecutionInput): Promise<ScheduledToolPreparation>
  /** Run only the around-dispatch/body stage. */
  dispatch(exec: ToolRunContext): Promise<ScheduledToolDispatch>
  /** Run ordered post-execute finalization, then materialize and notify the final outcome. */
  finalize(exec: ToolRunContext, result: ToolExecutionResult): Promise<ToolExecutionResult>
  /** Materialize and notify a final outcome that must bypass post-execute. */
  finish(exec: ToolRunContext, result: ToolExecutionResult): ToolExecutionResult
}

/**
 * Scheduler entry point omitted from the generated named service API.
 * @internal
 */
export const TOOL_REGISTRY_SCHEDULER: unique symbol = Symbol('@deepseek-ai/dsh-tools.scheduler')
/** Structured error metadata for a failed tool call (alongside the model-facing text). */
export interface ToolErrorInfo {
  name: string
  code: string
}

/**
 * Thrown (internally) when the model requests a tool that isn't registered.
 * Extends {@link HarnessError} (`code: 'UNKNOWN_TOOL'`) so an unknown-tool
 * failure is as routable as a tool-thrown one — retry/sandbox/replay code can
 * distinguish it from a tool body's own error.
 */
export class ToolNotFoundError extends HarnessError {
  constructor(toolName: string) {
    super(`unknown tool "${toolName}"`, 'UNKNOWN_TOOL')
    this.name = 'ToolNotFoundError'
  }
}

/** The outcome of one tool call. */
export interface ToolExecutionResult {
  content: ContentBlock[]
  isError: boolean
  /**
   * Set when the call failed with a {@link HarnessError}: machine-routable
   * `{ name, code }` for retry/sandbox plugins and replay. The model-facing
   * text in `content` is always present; this is extra structure for code.
   */
  error?: ToolErrorInfo
  /**
   * Model-facing context for the next request, separate from this tool result. The loop
   * accepts it into the active-batch FIFO, then appends after recorded results even if interrupted.
   */
  additionalContexts?: HookContext[]
  /**
   * The tool-private presentation payload from a successful `execute` (the object
   * return form). Threaded onto the `tool/result` session event and back into
   * {@link ToolResult} for `presentResult`. Opaque (`unknown`); absent when the
   * tool attached none or the call failed.
   */
  meta?: unknown
}

/**
 * Pre-dispatch decision. `allow` runs the call; `deny` materializes an error;
 * `ask` runs only after an approval service returns `allowed-once` and otherwise
 * denies. Input rewriting is excluded because arguments are already logged and
 * presented.
 */
export type PreToolDecision =
  | { kind: 'allow' }
  | { kind: 'deny'; reason: string }
  | { kind: 'ask'; reason?: string }

/**
 * Post-dispatch decision: accept or replace content, attach context for the next
 * request, or block by turning corrective feedback into an error result.
 */
export type PostToolDecision =
  | { kind: 'accept'; content?: ContentBlock[]; additionalContexts?: HookContext[] }
  | { kind: 'block'; feedback: ContentBlock[]; additionalContexts?: HookContext[] }

/**
 * Best-effort human-readable message from an arbitrary thrown value: Error
 * instances use `.message`; non-Error objects with a string `message`
 * property (e.g. `throw { message: 'denied' }`) use it too; everything else
 * is stringified.
 */
function errorMessage(error: unknown): string {
  try {
    if (error instanceof Error) return error.message
    if (typeof error === 'object' && error !== null
      && 'message' in error && typeof error.message === 'string') {
      return error.message
    }
    return String(error)
  } catch {
    // A hostile thrown value can trap `instanceof`, property access, or string
    // coercion. Error normalization is the outermost safety boundary, so its
    // fallback must itself be total.
    return '<unprintable thrown value>'
  }
}

/** Structured `{ name, code }` for a thrown HarnessError, else undefined. */
function errorInfo(error: unknown): ToolErrorInfo | undefined {
  try {
    return error instanceof HarnessError ? { name: error.name, code: error.code } : undefined
  } catch {
    return undefined
  }
}

/** How the registry presents its tools to the model (see {@link Config.mode}). */
export type ToolPresentationMode = 'native' | 'code' | 'both'

/** Plugin config: how the registered tools are presented to the model. */
export interface Config {
  /**
   * Model presentation. `native` (default) sends every visible schema; `code`
   * sends only `run_code` plus a generated SDK prompt; `both` sends both forms.
   * Code modes require a TypeScript runtime and fail prompt assembly when it is
   * absent or mismatched. Under `code`, native names in `toolOrder` are invalid.
   */
  mode?: ToolPresentationMode
}

/**
 * Per-scope filter over global tools. Restrictions intersect and do not affect
 * scoped registrations or the reserved Code Mode transport.
 */
export interface ToolRestriction {
  /** Global tool names that stay visible; everything else is removed. */
  readonly allow?: readonly string[]
  /** Global tool names removed from visibility. */
  readonly deny?: readonly string[]
}

/** One restriction compiled at registration for repeated live-global lookup. */
interface CompiledToolRestriction {
  readonly allow?: ReadonlySet<string>
  readonly deny?: ReadonlySet<string>
}

/** One scope's complete registry view, derived in a single layer traversal. */
interface ToolView {
  /** Visible definitions after restrictions, scoped shadowing, and transport insertion. */
  readonly visible: ReadonlyMap<string, ToolDefinition>
  /** Pre-restriction capability names used by prompt-order validation. */
  readonly knownNames: ReadonlySet<string>
  /** Current global names that a scoped restriction may name. */
  readonly restrictableNames: ReadonlySet<string>
}

/**
 * A monotonic execution guard evaluated after every `tools/pre-execute`
 * listener and before the tool body. Returning a reason denies the call;
 * returning `undefined` leaves it unchanged. Because guards have no allow
 * result, listener ordering cannot turn a denial back into permission.
 * @param execution - the identity-protected call after extensible pre-execute policy completed.
 * @returns a final denial reason, or `undefined` to leave the call allowed.
 */
export type ToolGuard = (execution: Readonly<ToolExecution>) => string | undefined

/** One guard registration; the wrapper preserves independent duplicate registrations. */
interface ToolGuardRegistration {
  guard: ToolGuard
}

/**
 * Tool registry and execution pipeline. Scoped registrations shadow globals;
 * one visibility resolver feeds presentation, lookup, and dispatch.
 */
export class ToolRegistry extends Service {
  static inject = ['systemPrompt']

  static Config: z<Config> = z.object({
    mode: z.union(['native', 'code', 'both'] as const).default('native'),
  })

  /** Internal staged view consumed by `dsh-agent-loop`'s parallel scheduler. */
  readonly [TOOL_REGISTRY_SCHEDULER]: ToolRegistryScheduler = {
    prepare: exec => this.prepareScheduledExecution(exec),
    dispatch: exec => this.dispatchScheduledExecution(exec),
    finalize: (exec, result) => this.finalizeScheduledExecution(exec, result),
    finish: (exec, result) => this.finishScheduledExecution(exec, result),
  }

  /** Context deferred by a running tool body, keyed by its scheduler-owned execution. */
  private deferredContexts = new WeakMap<ToolRunContext, HookContext[]>()
  private global = new Map<string, ToolDefinition>()
  private scoped = new Map<ScopeKey, Map<string, ToolDefinition>>()
  /** Compiled restriction filters, per scope (see {@link restrict}). */
  private restrictions = new Map<ScopeKey, CompiledToolRestriction[]>()
  /** Monotonic post-policy guards, split into global and per-agent layers. */
  private globalGuards = new Set<ToolGuardRegistration>()
  private scopedGuards = new Map<ScopeKey, Set<ToolGuardRegistration>>()
  private readonly mode: ToolPresentationMode
  /** Reserved presentation transport, kept outside the filterable registration layers. */
  private readonly codeTransport: ToolDefinition | undefined

  constructor(ctx: Context, config: Config = {}) {
    super(ctx, 'tools')
    // The schema already defaulted an omitted mode; the ?? narrows the
    // optional-input type for direct (non-Loader) construction in tests.
    this.mode = config.mode ?? 'native'
    // `run_code` is presentation infrastructure, not an end capability. It
    // therefore does not enter the global layer: per-agent restrictions must
    // not remove it, and a scoped registration must not shadow it. The
    // visibility resolver appends this reserved definition after resolving
    // the filterable global/scoped capability layers.
    this.codeTransport = this.mode === 'native'
      ? undefined
      : createRunCodeTool(this, () => this.requireCodeRuntime())
    ctx.systemPrompt.tools(context => this.wireSchemas(context.scope))
    if (this.mode !== 'native') {
      ctx.systemPrompt.section({
        name: 'tools:sdk',
        order: SDK_SECTION_ORDER,
        // Regenerate from the calling scope's visible tools in stable order.
        text: (context) => {
          this.requireCodeRuntime()
          return renderToolsSdk(this.schemas(context.scope).filter(schema => schema.name !== RUN_CODE_NAME))
        },
      })
    }
  }

  /**
   * Build one scope's wire schemas and names for prompt-order validation.
   * Restrictions do not make known tools invalid, but a mode collapse does.
   */
  private wireSchemas(scope?: ScopeKey): ToolProviderResult {
    const view = this.view(scope)
    const schemas = [...view.visible.values()].map(definition => this.schemaOf(definition, false))
    if (this.mode === 'native') {
      return { schemas, knownNames: [...view.knownNames] }
    }
    this.requireCodeRuntime()
    if (this.mode === 'code') {
      return {
        schemas: schemas.filter(schema => schema.name === RUN_CODE_NAME),
        knownNames: [RUN_CODE_NAME],
      }
    }
    return { schemas, knownNames: [...view.knownNames, RUN_CODE_NAME] }
  }

  /**
   * Resolve the code runtime or throw the actionable misconfiguration error.
   * Read at use time (assembly / run_code execution), NOT via static
   * `inject`: an inject entry would hold `ctx.tools` — and every tool plugin
   * behind it — hostage to a code runtime existing even under `mode:
   * 'native'` (the loop's optional-backend idiom, same as
   * `sessionPersistence`).
   */
  private requireCodeRuntime(): CodeRuntime {
    const runtime = this.ctx.get('codeRuntime')
    if (!runtime) {
      throw new Error(`dsh-tools: mode "${this.mode}" requires a code runtime — load a ctx.codeRuntime implementation (e.g. @deepseek-ai/dsh-code-runtime-worker) or set tools mode to "native"`)
    }
    if (runtime.language !== 'typescript') {
      throw new Error(`dsh-tools: mode "${this.mode}" generates a TypeScript SDK, but the loaded code runtime's language is "${runtime.language}"`)
    }
    return runtime
  }

  /**
   * Register globally or in the calling agent scope. Scoped tools shadow
   * globals; duplicates within one layer and the reserved `run_code` name fail.
   * @param definition - the tool schema, execution, and optional presentation functions.
   * @returns the exact disposer that unregisters the tool.
   */
  register(definition: ToolDefinition): () => void {
    const scope = scopeOf(this.ctx)
    const name = definition.name
    const timeoutMs = definition.timeoutMs
    if (timeoutMs !== undefined
      && (!Number.isFinite(timeoutMs) || timeoutMs <= 0)) {
      throw new TypeError(`tool "${name}" timeoutMs must be a positive finite number`)
    }
    if (this.codeTransport !== undefined && name === RUN_CODE_NAME) {
      throw new Error(`tool name "${RUN_CODE_NAME}" is reserved for the Code Mode presentation transport and cannot be registered or shadowed`)
    }
    const dispose = this.ctx.effect(function* (this: ToolRegistry) {
      const layer = scope === undefined ? this.global : this.layerFor(scope)
      if (layer.has(name)) {
        throw new Error(scope === undefined
          ? `tool "${name}" is already registered (for a per-agent variant, register through that agent's \`agent.ctx\` instead)`
          : `tool "${name}" is already registered in this scope`)
      }
      layer.set(name, definition)
      // Install rollback before notifying listeners.
      yield () => {
        layer.delete(name)
        // Drop empty scope layers.
        if (scope !== undefined && layer.size === 0) this.scoped.delete(scope)
        this.ctx.emit('tools/change')
      }
      this.ctx.emit('tools/change')
    }.bind(this), 'tools.register()')
    // Return the exact disposer so composite effects preserve teardown order.
    // eslint-disable-next-line @typescript-eslint/no-misused-promises -- synchronous cleanup; direct return preserves disposer identity
    return dispose
  }

  /**
   * Restrict global tools for the calling agent scope. Empty filters, unknown
   * names, scope-local names, and reserved transport names fail. Restrictions
   * intersect; scoped registrations remain visible.
   * @param filter - global-surface mask: `allow` (keep only) and/or `deny` (remove).
   * @returns the exact disposer that lifts this restriction.
   */
  restrict(filter: ToolRestriction): () => void {
    const scope = scopeOf(this.ctx)
    if (scope === undefined) {
      throw new Error('tools.restrict() requires a scoped context (agent.ctx): a context-global restriction would mask every agent — deny the tool for the intended agent instead')
    }
    const allow = filter.allow
    const deny = filter.deny
    if (allow === undefined && deny === undefined) {
      throw new Error('tools.restrict({}) is a no-op: pass `allow` and/or `deny` (an empty filter is almost always a materialized-empty-config bug)')
    }
    const compiled: CompiledToolRestriction = {
      ...allow !== undefined ? { allow: new Set(allow) } : {},
      ...deny !== undefined ? { deny: new Set(deny) } : {},
    }
    if (this.codeTransport !== undefined
      && [...allow ?? [], ...deny ?? []].includes(RUN_CODE_NAME)) {
      throw new Error(`tools.restrict() cannot name reserved Code Mode presentation transport "${RUN_CODE_NAME}"; restrict end-capability tools instead`)
    }
    const known = this.view(scope).restrictableNames
    const unknown = [...allow ?? [], ...deny ?? []].filter(name => !known.has(name))
    if (unknown.length > 0) {
      throw new Error(`tools.restrict() names unknown global tool${unknown.length > 1 ? 's' : ''} ${unknown.map(n => `"${n}"`).join(', ')}; known global tools: ${[...known].sort().join(', ') || '(none)'}`)
    }
    const dispose = this.ctx.effect(function* (this: ToolRegistry) {
      const list = this.restrictions.get(scope) ?? []
      this.restrictions.set(scope, list)
      list.push(compiled)
      yield () => {
        const index = list.indexOf(compiled)
        /* v8 ignore next 3 -- defensive: the compiled restriction was pushed, so indexOf is guaranteed >= 0 */
        if (index >= 0) list.splice(index, 1)
        if (list.length === 0) this.restrictions.delete(scope)
        this.ctx.emit('tools/change')
      }
      this.ctx.emit('tools/change')
    }.bind(this), 'tools.restrict()')
    // Return the exact disposer so composite effects preserve teardown order.
    // eslint-disable-next-line @typescript-eslint/no-misused-promises -- synchronous cleanup; direct return preserves disposer identity
    return dispose
  }

  /**
   * Register a monotonic guard after the extensible `tools/pre-execute`
   * waterfall. A plain-context guard applies globally; one registered through
   * `agent.ctx` applies only to that agent. Any matching guard may deny by
   * returning a reason, while no guard can force-allow a call another guard
   * denied. The exact effect disposer is returned for ordered ownership and
   * HMR cleanup.
   * @param guard - synchronous check; a returned string denies the execution.
   * @returns the exact disposer that unregisters the guard.
   */
  guard(guard: ToolGuard): () => void {
    const scope = scopeOf(this.ctx)
    const registration = { guard }
    const dispose = this.ctx.effect(function* (this: ToolRegistry) {
      const layer = scope === undefined ? this.globalGuards : this.guardLayerFor(scope)
      layer.add(registration)
      yield () => {
        layer.delete(registration)
        if (scope !== undefined && layer.size === 0) this.scopedGuards.delete(scope)
      }
    }.bind(this), 'tools.guard()')
    // eslint-disable-next-line @typescript-eslint/no-misused-promises -- synchronous cleanup; direct return preserves disposer identity
    return dispose
  }

  /** The (created-on-demand) scoped layer for `scope`. */
  private layerFor(scope: ScopeKey): Map<string, ToolDefinition> {
    let layer = this.scoped.get(scope)
    if (!layer) {
      layer = new Map()
      this.scoped.set(scope, layer)
    }
    return layer
  }

  /** Get or create the guard layer for one agent scope. */
  private guardLayerFor(scope: ScopeKey): Set<ToolGuardRegistration> {
    let layer = this.scopedGuards.get(scope)
    if (layer === undefined) {
      layer = new Set()
      this.scopedGuards.set(scope, layer)
    }
    return layer
  }

  /** First monotonic denial from the global then matching scoped guard layers. */
  private guardReason(exec: ToolExecution): string | undefined {
    for (const { guard } of this.globalGuards) {
      const reason = guard(exec)
      if (reason !== undefined) return reason
    }
    if (exec.agent !== undefined) {
      for (const { guard } of this.scopedGuards.get(exec.agent) ?? []) {
        const reason = guard(exec)
        if (reason !== undefined) return reason
      }
    }
    return undefined
  }

  /** Whether every restriction registered for `scope` admits the global tool `name` (intersection semantics). */
  private admits(scope: ScopeKey | undefined, name: string): boolean {
    if (scope === undefined) return true
    const filters = this.restrictions.get(scope)
    if (!filters) return true
    return filters.every(filter =>
      (filter.allow === undefined || filter.allow.has(name))
      && (filter.deny === undefined || !filter.deny.has(name)))
  }

  /**
   * Resolve every registry fact one scope needs in one layer traversal. The
   * visible map applies global restrictions, scoped shadowing, and the reserved
   * presentation transport; the other sets retain the pre-restriction facts
   * needed by restriction and prompt-order validation.
   * @param scope - the viewing scope (the agent), or undefined for the global view.
   * @returns the complete derived view for that scope.
   */
  private view(scope?: ScopeKey): ToolView {
    const layer = scope === undefined ? undefined : this.scoped.get(scope)
    const visible = new Map<string, ToolDefinition>()
    const knownNames = new Set<string>()
    const restrictableNames = new Set<string>()
    for (const [name, definition] of this.global) {
      knownNames.add(name)
      restrictableNames.add(name)
      if (this.admits(scope, name)) visible.set(name, definition)
    }
    // Scoped layer second: same-name entries REPLACE (shadow) the global ones,
    // and scope-local registrations are never part of the global filter above.
    for (const [name, definition] of layer ?? []) {
      knownNames.add(name)
      visible.set(name, definition)
    }
    // Presentation infrastructure is resolved last and outside capability
    // filtering. Registration rejects this reserved name, so the insertion is
    // an invariant assertion as well as protection against future layer changes.
    if (this.codeTransport !== undefined) {
      visible.set(RUN_CODE_NAME, this.codeTransport)
    }
    return { visible, knownNames, restrictableNames }
  }

  /**
   * Look up a tool as one scope sees it (scoped
   * shadows global; a restricted-away global reads as absent). Presenters pass
   * the calling agent so the rendered card matches the definition that
   * actually executed.
   * @param name - the tool name as registered.
   * @param scope - the viewing scope (the agent); omitted = the global view.
   * @returns the definition the scope resolves, or undefined when none is visible.
   */
  get(name: string, scope?: ScopeKey): ToolDefinition | undefined {
    return this.view(scope).visible.get(name)
  }

  /**
   * Project visible definitions onto the allowlisted model-facing schema fields,
   * excluding execution and presentation callbacks.
   * @param scope - the viewing scope (the agent); omitted = the global view.
   * @returns one deep-cloned schema per visible tool.
   */
  schemas(scope?: ScopeKey): ToolSchema[] {
    return [...this.view(scope).visible.values()].map(definition => this.schemaOf(definition, true))
  }

  /** Project one definition onto the model-facing schema fields. */
  private schemaOf(definition: ToolDefinition, detachParameters: boolean): ToolSchema {
    const { name, description, parameters } = definition
    return {
      name,
      description,
      parameters: detachParameters ? structuredClone(parameters) : parameters,
    }
  }

  /**
   * Classify a pending call through the caller's visible tool definition. Only
   * an exact `true` is parallel; unknown, hidden, undeclared, invalid, or
   * throwing classifiers are exclusive.
   * @param exec - call name, parsed arguments, and optional agent scope.
   * @returns the fail-closed scheduling mode.
   */
  executionMode(exec: ToolExecutionInput): ToolExecutionMode {
    const tool = this.get(exec.name, exec.agent)
    if (!tool?.isConcurrencySafe) return { kind: 'exclusive' }
    try {
      const concurrencySafe: unknown = tool.isConcurrencySafe(exec.arguments)
      return concurrencySafe === true ? { kind: 'parallel' } : { kind: 'exclusive' }
    } catch {
      return { kind: 'exclusive' }
    }
  }

  /**
   * Execute through pre-policy, guards, around-dispatch, post-policy, and final
   * notification. Tool and listener failures resolve as materialized error
   * results; an invisible tool reports `UNKNOWN_TOOL`. The returned outcome is
   * the same lossless, frozen snapshot final observers receive.
   * @param exec - the typed same-process call input. The registry assigns its
   *   correlation token before policy begins.
   * @returns the materialized final result.
   */
  async execute(exec: ToolExecutionInput): Promise<ToolExecutionResult> {
    return this.prepareExecution(exec, prepared => this.completeScheduledExecution(prepared))
  }

  private async completeScheduledExecution(prepared: ScheduledToolPreparation): Promise<ToolExecutionResult> {
    switch (prepared.kind) {
      case 'dispatch': {
        const dispatched = await this.dispatchScheduledExecution(prepared.exec)
        return dispatched.kind === 'post-result'
          ? await this.finalizeScheduledExecution(prepared.exec, dispatched.result)
          : this.finishScheduledExecution(prepared.exec, dispatched.result)
      }
      case 'post-result':
        return await this.finalizeScheduledExecution(prepared.exec, prepared.result)
      case 'final-result':
        return this.finishScheduledExecution(prepared.exec, prepared.result)
      /* v8 ignore next -- closed-union exhaustiveness guard */
      default:
        return assertNever(prepared, 'scheduled tool preparation')
    }
  }

  private createExecution(exec: ToolExecutionInput): ScheduledToolPreparation | { kind: 'ready'; exec: ToolRunContext } {
    const deferredContexts: HookContext[] = []
    const token = createExecutionToken()
    const callId = exec.callId
    const name = exec.name
    const agent = exec.agent
    const parent = exec.parent
    const signal = exec.signal
    const base = {
      token,
      callId,
      name,
      ...agent !== undefined ? { agent } : {},
      ...parent !== undefined ? { parent } : {},
      ...signal !== undefined ? { signal } : {},
      deferContext(context: HookContext): void {
        deferredContexts.push(context)
      },
    }
    try {
      const detached = snapshotJsonValue(exec.arguments)
      if (detached === undefined) {
        throw new TypeError('tool execution arguments must be losslessly JSON-serializable')
      }
      const execution: ToolRunContext = { ...base, arguments: deepFreeze(detached) }
      this.deferredContexts.set(execution, deferredContexts)
      return { kind: 'ready', exec: execution }
    } catch (error: unknown) {
      const execution: ToolRunContext = { ...base, arguments: undefined }
      return { kind: 'final-result', exec: execution, result: toolErrorResult(error) }
    }
  }

  /**
   * Run the ordered pre-execute and monotonic guard stages for the scheduler.
   * @param input - the caller-supplied execution input.
   * @returns the prepared execution plus the next scheduler stage.
   * @internal
   */
  private async prepareScheduledExecution(input: ToolExecutionInput): Promise<ScheduledToolPreparation> {
    return this.prepareExecution(input, prepared => prepared)
  }

  private async prepareExecution<T>(
    input: ToolExecutionInput,
    next: (prepared: ScheduledToolPreparation) => T | PromiseLike<T>,
  ): Promise<T> {
    const created = this.createExecution(input)
    if (created.kind !== 'ready') return next(created)
    const exec = created.exec
    try {
      const carrier = scopeTarget(this, exec.agent)
      const gate = await this.ctx.waterfall(
        carrier, 'tools/pre-execute', exec,
        () => Promise.resolve<PreToolDecision>({ kind: 'allow' }),
      )
      const decision = gate.kind === 'ask' ? await this.serviceAsk(exec, gate) : gate
      const denialReason = decision.kind === 'allow'
        ? this.guardReason(exec)
        : decision.reason
      if (denialReason !== undefined) {
        return await next({
          kind: 'post-result',
          exec,
          result: {
            content: [{ type: 'text', text: `Error: ${denialReason}` }],
            isError: true,
          },
        })
      }
      return await next({ kind: 'dispatch', exec })
    } catch (error: unknown) {
      return next({ kind: 'final-result', exec, result: toolErrorResult(error) })
    }
  }

  /**
   * Run around-dispatch and the tool body. Tool and unknown-tool failures still
   * receive post-execute; pipeline failures are already final.
   * @param exec - the prepared execution.
   * @returns whether the result still needs post-execute.
   * @internal
   */
  private async dispatchScheduledExecution(exec: ToolRunContext): Promise<ScheduledToolDispatch> {
    try {
      const carrier = scopeTarget(this, exec.agent)
      const result = await this.ctx.waterfall(
        carrier, 'tools/execute', exec,
        async (): Promise<ToolExecutionResult> => {
          try {
            const tool = this.get(exec.name, exec.agent)
            if (!tool) throw new ToolNotFoundError(exec.name)
            const returned = await tool.execute(exec.arguments, exec)
            const content = Array.isArray(returned) ? returned : returned.content
            const meta = Array.isArray(returned) ? undefined : returned.meta
            return { content, isError: false, ...meta !== undefined ? { meta } : {} }
          } catch (error: unknown) {
            return toolErrorResult(error)
          }
        },
      )
      const deferredContexts = this.deferredContexts.get(exec)
      /* v8 ignore next -- dispatch only receives executions minted by this registry's prepare stage */
      if (deferredContexts === undefined) throw new Error('tool registry scheduler invariant violated: unprepared execution')
      const resultWithDeferredContexts: ToolExecutionResult = deferredContexts.length === 0
        ? result
        : {
          ...result,
          additionalContexts: [
            ...deferredContexts,
            ...result.additionalContexts ?? [],
          ],
        }
      return { kind: 'post-result', result: resultWithDeferredContexts }
    } catch (error: unknown) {
      return { kind: 'final-result', result: toolErrorResult(error) }
    }
  }

  /**
   * Run ordered post-execute, then materialize and notify the final outcome.
   * @param exec - the prepared execution.
   * @param result - dispatch/pre result that still needs post-execute.
   * @returns the materialized final result.
   * @internal
   */
  private async finalizeScheduledExecution(exec: ToolRunContext, result: ToolExecutionResult): Promise<ToolExecutionResult> {
    try {
      return this.finishScheduledExecution(exec, await this.postExecute(exec, result))
    } catch (error: unknown) {
      return this.finishScheduledExecution(exec, toolErrorResult(error))
    }
  }

  /**
   * Materialize and notify a final result that must bypass post-execute.
   * @param exec - the prepared execution.
   * @param result - final result.
   * @returns the materialized final result.
   * @internal
   */
  private finishScheduledExecution(exec: ToolRunContext, result: ToolExecutionResult): ToolExecutionResult {
    let finalResult: ToolExecutionResult
    try {
      finalResult = this.materializeFinalResult(result)
    } catch (error: unknown) {
      finalResult = this.materializeFinalResult(toolErrorResult(error))
    }
    this.notifyResult(exec, finalResult)
    return finalResult
  }

  /** Notify observers without exposing a mutation or error channel into the outcome. */
  private notifyResult(exec: ToolExecution, result: ToolExecutionResult): void {
    // Freeze the remaining mutable signal slot before observers receive the
    // shared WeakMap-keyable execution object.
    Object.freeze(exec)
    const { name: toolName, callId } = exec
    const reportFailure = (error: unknown): void => {
      this.ctx.logger.warn(`tool "${toolName}" (${callId}): tools/result observer failed: ${errorMessage(error)}`)
    }
    const callbacks = this.ctx.events.dispatch('emit', [
      scopeTarget(this, exec.agent), 'tools/result', exec, result,
    ])
    for (const callback of callbacks) {
      try {
        const returned: unknown = callback(exec, result)
        void Promise.resolve(returned).catch(reportFailure)
      } catch (error: unknown) {
        reportFailure(error)
      }
    }
  }

  /**
   * Resolve an `ask` decision to allow/deny through the approval seam. The
   * seam is consumed opportunistically with `ctx.get('approval')` — a
   * deployment that composes no ApprovalService keeps the historical degrade
   * to deny, and an unmount mid-session degrades the same way on the next ask.
   * An agent-less execution also degrades: without an agent there is no
   * session to audit to and no UI to route to. Otherwise the outcome maps
   * one-to-one — `allowed-once` proceeds; the three non-grants deny with
   * distinct reasons so the model can tell a human "no" from an absent
   * approval channel.
   */
  private async serviceAsk(
    exec: ToolExecution,
    ask: Extract<PreToolDecision, { kind: 'ask' }>,
  ): Promise<Extract<PreToolDecision, { kind: 'allow' | 'deny' }>> {
    const approval = this.ctx.get('approval')
    if (approval === undefined) {
      return { kind: 'deny', reason: ask.reason ?? `tool "${exec.name}" requires approval (not yet supported)` }
    }
    if (exec.agent === undefined) {
      return { kind: 'deny', reason: `tool "${exec.name}" requires approval, but the call has no agent to route it through` }
    }
    const outcome = await approval.request({
      agent: exec.agent,
      toolName: exec.name,
      callId: exec.callId,
      ...ask.reason !== undefined ? { reason: ask.reason } : {},
      ...exec.signal !== undefined ? { signal: exec.signal } : {},
    })
    switch (outcome) {
      case 'allowed-once': return { kind: 'allow' }
      case 'rejected': return { kind: 'deny', reason: `the user rejected tool "${exec.name}"` }
      case 'cancelled': return { kind: 'deny', reason: `approval for tool "${exec.name}" was cancelled` }
      case 'unavailable': return { kind: 'deny', reason: `tool "${exec.name}" requires approval, but no approval channel is available` }
      default: return assertNever(outcome, 'ApprovalOutcome')
    }
  }

  /**
   * Run the `tools/post-execute` waterfall over a dispatched `result` and apply
   * its {@link PostToolDecision}: `accept` keeps the call successful (replacing
   * `content` when given), `block` turns it into an `isError` whose content is
   * the corrective `feedback`. Either decision may attach `additionalContexts`,
   * which are ferried on the returned result for the loop's active-batch FIFO.
   * Context deferred by the tool body survives an accepted result but is
   * discarded when the outer call is blocked; a block exposes only context the
   * blocking decision explicitly supplied.
   * Runs inside `execute`'s outer try/catch (a throwing listener → isError).
   */
  private async postExecute(exec: ToolExecution, result: ToolExecutionResult): Promise<ToolExecutionResult> {
    const decision = await this.ctx.waterfall(
      scopeTarget(this, exec.agent), 'tools/post-execute', exec, result,
      () => Promise.resolve<PostToolDecision>({ kind: 'accept' }),
    )
    const decisionContexts = decision.additionalContexts ?? []
    if (decision.kind === 'block') {
      return {
        content: decision.feedback,
        isError: true,
        ...decisionContexts.length > 0 ? { additionalContexts: decisionContexts } : {},
      }
    }
    // Accept: replace content if supplied, preserve the dispatched outcome, and
    // append decision contexts after contexts deferred by the tool body.
    const additionalContexts = [
      ...result.additionalContexts ?? [],
      ...decisionContexts,
    ]
    return {
      ...result,
      ...decision.content ? { content: decision.content } : {},
      ...additionalContexts.length > 0 ? { additionalContexts } : {},
    }
  }

  /** Materialize the authoritative commit outcome once, immediately before `tools/result`. */
  private materializeFinalResult(result: ToolExecutionResult): ToolExecutionResult {
    const detached = snapshotJsonValue(result)
    if (detached === undefined) {
      throw new TypeError('tool result must be losslessly JSON-serializable')
    }
    return deepFreeze(detached)
  }
}

/** Mint a same-process correlation token whose identity is its value. */
function createExecutionToken(): ToolExecutionToken {
  return Symbol('dsh.tool.execution') as ToolExecutionToken
}

function toolErrorResult(error: unknown): ToolExecutionResult {
  const info = errorInfo(error)
  return {
    content: [{ type: 'text', text: `Error: ${errorMessage(error)}` }],
    isError: true,
    ...info ? { error: info } : {},
  }
}

export default ToolRegistry