feat: follow an epic with everything under it

«Seguir todo» on a ticket with subtasks (and on each epic of the Epics
page) tells you of it and of every ticket hanging from it, at any depth,
also the ones added later: their moves, assignments, comments and plan
changes, as a follower of each, plus when a ticket is placed under it.
Guests of a private project are left out. Personal, no history (Mongo
`tree_follows`).

API: followTree / unfollowTree, Issue.followingTree, PUT/DELETE
/api/issues/{issue}/follow-tree. MCP: watch_issue with tree.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

libs/web/tracker/infrastructure/src/lib/adapters/graphql-issues.gateway.ts

@@ -51,6 +51,8 @@ import {
   VoteIssueDocument,
   WatchIssueDocument,
   MyPinsDocument,
+  FollowTreeDocument,
+  UnfollowTreeDocument,
   SearchDecisionsDocument,
   PinIssueDocument,
   UpdateChecklistItemDocument,
@@ -218,6 +220,13 @@ export class GraphqlIssuesGateway extends IssuesGateway {
         ),
       );
   }
+  followTree(issueId: string, on: boolean): Observable<void> {
+    const done$: Observable<unknown> = on
+      ? this.gql.mutate(FollowTreeDocument, { issueId })
+      : this.gql.mutate(UnfollowTreeDocument, { issueId });
+    return done$.pipe(map(() => undefined));
+  }
+
   pin(issueId: string, pinned: boolean): Observable<void> {
     const done$: Observable<unknown> = pinned
       ? this.gql.mutate(PinIssueDocument, { issueId })
@@ -259,6 +268,7 @@ export class GraphqlIssuesGateway extends IssuesGateway {
           issue: toIssueSummary(epic.issue),
           progress: { ...epic.progress },
           links: epic.issue.links.map((l) => toIssueLink(l)),
+          followingTree: epic.issue.followingTree,
         })),
       ),
     );

libs/web/tracker/infrastructure/src/lib/adapters/graphql-projects.gateway.ts

@@ -85,6 +85,8 @@ export class GraphqlProjectsGateway extends ProjectsGateway {
             issue: toIssueSummary(e.issue),
             progress: { ...e.progress },
             links: [],
+            // The portfolio does not offer following.
+            followingTree: false,
           })),
         })),
       ),

libs/web/tracker/infrastructure/src/lib/graphql/fragments.graphql

@@ -121,6 +121,7 @@ fragment IssueSummaryFields on Issue {
 fragment IssueFields on Issue {
   ...IssueSummaryFields
   pinned
+  followingTree
   decisions {
     ...CommentFields
   }

libs/web/tracker/infrastructure/src/lib/graphql/generated.ts

@@ -688,6 +688,7 @@ export type IssueSummaryFieldsFragment = {
 
 export type IssueFieldsFragment = {
   pinned: boolean;
+  followingTree: boolean;
   description: string | null;
   figmaUrl: string | null;
   createdAt: string;
@@ -933,6 +934,7 @@ export type IssueQueryVariables = Exact<{
 export type IssueQuery = {
   issue: {
     pinned: boolean;
+    followingTree: boolean;
     description: string | null;
     figmaUrl: string | null;
     createdAt: string;
@@ -1151,6 +1153,18 @@ export type MyPinsQuery = {
   }>;
 };
 
+export type FollowTreeMutationVariables = Exact<{
+  issueId: string;
+}>;
+
+export type FollowTreeMutation = { followTree: boolean };
+
+export type UnfollowTreeMutationVariables = Exact<{
+  issueId: string;
+}>;
+
+export type UnfollowTreeMutation = { unfollowTree: boolean };
+
 export type PinIssueMutationVariables = Exact<{
   issueId: string;
 }>;
@@ -1321,6 +1335,7 @@ export type EpicsQueryVariables = Exact<{
 export type EpicsQuery = {
   epics: Array<{
     issue: {
+      followingTree: boolean;
       id: string;
       projectId: string;
       key: string;
@@ -3820,6 +3835,7 @@ export const IssueFieldsFragmentDoc = {
             name: { kind: 'Name', value: 'IssueSummaryFields' },
           },
           { kind: 'Field', name: { kind: 'Name', value: 'pinned' } },
+          { kind: 'Field', name: { kind: 'Name', value: 'followingTree' } },
           {
             kind: 'Field',
             name: { kind: 'Name', value: 'decisions' },
@@ -6420,6 +6436,7 @@ export const IssueDocument = {
             name: { kind: 'Name', value: 'IssueSummaryFields' },
           },
           { kind: 'Field', name: { kind: 'Name', value: 'pinned' } },
+          { kind: 'Field', name: { kind: 'Name', value: 'followingTree' } },
           {
             kind: 'Field',
             name: { kind: 'Name', value: 'decisions' },
@@ -7452,6 +7469,93 @@ export const MyPinsDocument = {
     },
   ],
 } as unknown as DocumentNode<MyPinsQuery, MyPinsQueryVariables>;
+export const FollowTreeDocument = {
+  kind: 'Document',
+  definitions: [
+    {
+      kind: 'OperationDefinition',
+      operation: 'mutation',
+      name: { kind: 'Name', value: 'FollowTree' },
+      variableDefinitions: [
+        {
+          kind: 'VariableDefinition',
+          variable: {
+            kind: 'Variable',
+            name: { kind: 'Name', value: 'issueId' },
+          },
+          type: {
+            kind: 'NonNullType',
+            type: { kind: 'NamedType', name: { kind: 'Name', value: 'ID' } },
+          },
+        },
+      ],
+      selectionSet: {
+        kind: 'SelectionSet',
+        selections: [
+          {
+            kind: 'Field',
+            name: { kind: 'Name', value: 'followTree' },
+            arguments: [
+              {
+                kind: 'Argument',
+                name: { kind: 'Name', value: 'issueId' },
+                value: {
+                  kind: 'Variable',
+                  name: { kind: 'Name', value: 'issueId' },
+                },
+              },
+            ],
+          },
+        ],
+      },
+    },
+  ],
+} as unknown as DocumentNode<FollowTreeMutation, FollowTreeMutationVariables>;
+export const UnfollowTreeDocument = {
+  kind: 'Document',
+  definitions: [
+    {
+      kind: 'OperationDefinition',
+      operation: 'mutation',
+      name: { kind: 'Name', value: 'UnfollowTree' },
+      variableDefinitions: [
+        {
+          kind: 'VariableDefinition',
+          variable: {
+            kind: 'Variable',
+            name: { kind: 'Name', value: 'issueId' },
+          },
+          type: {
+            kind: 'NonNullType',
+            type: { kind: 'NamedType', name: { kind: 'Name', value: 'ID' } },
+          },
+        },
+      ],
+      selectionSet: {
+        kind: 'SelectionSet',
+        selections: [
+          {
+            kind: 'Field',
+            name: { kind: 'Name', value: 'unfollowTree' },
+            arguments: [
+              {
+                kind: 'Argument',
+                name: { kind: 'Name', value: 'issueId' },
+                value: {
+                  kind: 'Variable',
+                  name: { kind: 'Name', value: 'issueId' },
+                },
+              },
+            ],
+          },
+        ],
+      },
+    },
+  ],
+} as unknown as DocumentNode<
+  UnfollowTreeMutation,
+  UnfollowTreeMutationVariables
+>;
 export const PinIssueDocument = {
   kind: 'Document',
   definitions: [
@@ -8633,6 +8737,10 @@ export const EpicsDocument = {
                         kind: 'FragmentSpread',
                         name: { kind: 'Name', value: 'IssueSummaryFields' },
                       },
+                      {
+                        kind: 'Field',
+                        name: { kind: 'Name', value: 'followingTree' },
+                      },
                       {
                         kind: 'Field',
                         name: { kind: 'Name', value: 'links' },

libs/web/tracker/infrastructure/src/lib/graphql/issues.graphql

@@ -101,6 +101,14 @@ query MyPins {
   }
 }
 
+mutation FollowTree($issueId: ID!) {
+  followTree(issueId: $issueId)
+}
+
+mutation UnfollowTree($issueId: ID!) {
+  unfollowTree(issueId: $issueId)
+}
+
 mutation PinIssue($issueId: ID!) {
   pinIssue(issueId: $issueId)
 }
@@ -185,6 +193,7 @@ query Epics($projectId: ID!) {
   epics(projectId: $projectId) {
     issue {
       ...IssueSummaryFields
+      followingTree
       links {
         type
         direction