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agentcore dev -p <port> is silently offset by runtime index when running multiple runtimes in parallel #1079

Closed
#1661
Closed
agentcore dev -p <port> is silently offset by runtime index when running multiple runtimes in parallel#1079
#1661
Assignees
avi-alpert
Labels
bugSomething isn't working

Description

@masaha03
masaha03
opened on May 1, 2026

Description

When running multiple agentcore dev instances in parallel, getAgentPort() in
src/cli/operations/dev/config.ts silently offsets the port passed via
-p by the runtime's index in agentcore.json (basePort + runtimeIndex). The shift is not logged and the flag's help text ("Port for development server") gives no hint that -p is a base port.

Why this is a problem

The actual bound port depends on which other runtimes are configured in agentcore.json and which ones happen to be running, not just on the -p value.
This breaks local development and integration testing in practical ways:

  • Downstream services (backend servers, integration tests, scripts) that target http://localhost:<-p value>/invocations silently talk to the wrong port —
    or get connection errors — depending on which runtimes are up.
  • Which runtime owns which port changes if someone reorders, adds, or removes entries in agentcore.json. A config-only change silently breaks every
    developer's local setup.
  • To hit a specific port, a user has to compute -p = desiredPort - runtimeIndex and keep that in sync with agentcore.json. The -p value in
    package.json / README / CI scripts no longer means what it says.
  • A second free-port search (findFreePort in src/cli/operations/dev/utils.ts) can shift the port again if basePort + index is occupied, and only
    that shift is announced. The first, index-based shift is invisible.

Suggested Fixes (any one resolves the surprise)

  1. Treat -p as the literal port; fail fast on conflict.
  2. Add a per-runtime devPort field in agentcore.json so the mapping is explicit and stable across reorderings.
  3. Log the offset whenever getAgentPort shifts the port, mirroring the existing Port ${ee} in use, using ${re} message.
  4. At minimum, document the current behavior in --help and the README.

Steps to Reproduce

  1. agentcore.json with two runtimes: 
    { "runtimes": [{ "name": "AgentA", ... }, { "name": "AgentB", ... }] }
  2. Run both in parallel with the ports you actually want: 
    agentcore dev -r AgentA -p 8787 &
agentcore dev -r AgentB -p 8788 &
  3. lsof -iTCP -sTCP:LISTEN -n -P — AgentB is on 8789, not 8788.

Expected Behavior

AgentB binds to 8788 (the value passed via -p).

Actual Behavior

AgentB binds to 8789 (8788 + index(AgentB) = 8788 + 1). No log line explains why.

CLI Version

@aws/agentcore@0.12.0; logic still on main / v0.13.0.

Operating System

macOS

Additional Context

No response

Metadata

Metadata

Assignees

Labels

bugSomething isn't working

Type

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Projects

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    Milestone

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agentcore dev -p <port> is silently offset by runtime index when running multiple runtimes in parallel · Issue #1079 · aws/agentcore-cli · GitHub
    Skip to content
    agentcore dev -p <port> is silently offset by runtime index when running multiple runtimes in parallel #1079
    Closed
    #1661
    Closed
    agentcore dev -p <port> is silently offset by runtime index when running multiple runtimes in parallel#1079
    #1661
    Assignees
    avi-alpert
    Labels
    bugSomething isn't working
    Description
    @masaha03
    masaha03
    opened on May 1, 2026
    Description
    When running multiple agentcore dev instances in parallel, getAgentPort() in
    src/cli/operations/dev/config.ts silently offsets the port passed via
    -p by the runtime's index in agentcore.json (basePort + runtimeIndex). The shift is not logged and the flag's help text ("Port for development server") gives no hint that -p is a base port.
    Why this is a problem
    The actual bound port depends on which other runtimes are configured in agentcore.json and which ones happen to be running, not just on the -p value.
    
This breaks local development and integration testing in practical ways:
    • Downstream services (backend servers, integration tests, scripts) that target http://localhost:<-p value>/invocations silently talk to the wrong port —
      
or get connection errors — depending on which runtimes are up.
    • Which runtime owns which port changes if someone reorders, adds, or removes entries in agentcore.json. A config-only change silently breaks every
      
developer's local setup.
    • To hit a specific port, a user has to compute -p = desiredPort - runtimeIndex and keep that in sync with agentcore.json. The -p value in
      package.json / README / CI scripts no longer means what it says.
    • A second free-port search (findFreePort in src/cli/operations/dev/utils.ts) can shift the port again if basePort + index is occupied, and only
      
that shift is announced. The first, index-based shift is invisible.
    Suggested Fixes (any one resolves the surprise)
    1. Treat -p as the literal port; fail fast on conflict.
    2. Add a per-runtime devPort field in agentcore.json so the mapping is explicit and stable across reorderings.
    3. Log the offset whenever getAgentPort shifts the port, mirroring the existing Port ${ee} in use, using ${re} message.
    4. At minimum, document the current behavior in --help and the README.
    Steps to Reproduce
    1. agentcore.json with two runtimes:

      { "runtimes": [{ "name": "AgentA", ... }, { "name": "AgentB", ... }] }
    2. Run both in parallel with the ports you actually want:

      agentcore dev -r AgentA -p 8787 &
agentcore dev -r AgentB -p 8788 &
    3. lsof -iTCP -sTCP:LISTEN -n -P — AgentB is on 8789, not 8788.
    Expected Behavior
    AgentB binds to 8788 (the value passed via -p).
    Actual Behavior
    AgentB binds to 8789 (8788 + index(AgentB) = 8788 + 1). No log line explains why.
    CLI Version
    @aws/agentcore@0.12.0; logic still on main / v0.13.0.
    Operating System
    macOS
    Additional Context
    No response
    Metadata
    Metadata
    Assignees
    Labels
    bugSomething isn't working
    Type
    No type
    Projects
    No projects
      Milestone
      No milestone
      Relationships
      None yet
      Development
      No branches or pull requests
      Issue actions
      
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agentcore dev -p <port> is silently offset by runtime index when running multiple runtimes in parallel · Issue #1079 · aws/agentcore-cli · GitHub
      Skip to content
      agentcore dev -p <port> is silently offset by runtime index when running multiple runtimes in parallel #1079
      Closed
      #1661
      Closed
      agentcore dev -p <port> is silently offset by runtime index when running multiple runtimes in parallel#1079
      #1661
      Assignees
      avi-alpert
      Labels
      bugSomething isn't working
      Description
      @masaha03
      masaha03
      opened on May 1, 2026
      Description
      When running multiple agentcore dev instances in parallel, getAgentPort() in
      src/cli/operations/dev/config.ts silently offsets the port passed via
      -p by the runtime's index in agentcore.json (basePort + runtimeIndex). The shift is not logged and the flag's help text ("Port for development server") gives no hint that -p is a base port.
      Why this is a problem
      The actual bound port depends on which other runtimes are configured in agentcore.json and which ones happen to be running, not just on the -p value.
      
This breaks local development and integration testing in practical ways:
      • Downstream services (backend servers, integration tests, scripts) that target http://localhost:<-p value>/invocations silently talk to the wrong port —
        
or get connection errors — depending on which runtimes are up.
      • Which runtime owns which port changes if someone reorders, adds, or removes entries in agentcore.json. A config-only change silently breaks every
        
developer's local setup.
      • To hit a specific port, a user has to compute -p = desiredPort - runtimeIndex and keep that in sync with agentcore.json. The -p value in
        package.json / README / CI scripts no longer means what it says.
      • A second free-port search (findFreePort in src/cli/operations/dev/utils.ts) can shift the port again if basePort + index is occupied, and only
        
that shift is announced. The first, index-based shift is invisible.
      Suggested Fixes (any one resolves the surprise)
      1. Treat -p as the literal port; fail fast on conflict.
      2. Add a per-runtime devPort field in agentcore.json so the mapping is explicit and stable across reorderings.
      3. Log the offset whenever getAgentPort shifts the port, mirroring the existing Port ${ee} in use, using ${re} message.
      4. At minimum, document the current behavior in --help and the README.
      Steps to Reproduce
      1. agentcore.json with two runtimes:

        { "runtimes": [{ "name": "AgentA", ... }, { "name": "AgentB", ... }] }
      2. Run both in parallel with the ports you actually want:

        agentcore dev -r AgentA -p 8787 &
agentcore dev -r AgentB -p 8788 &
      3. lsof -iTCP -sTCP:LISTEN -n -P — AgentB is on 8789, not 8788.
      Expected Behavior
      AgentB binds to 8788 (the value passed via -p).
      Actual Behavior
      AgentB binds to 8789 (8788 + index(AgentB) = 8788 + 1). No log line explains why.
      CLI Version
      @aws/agentcore@0.12.0; logic still on main / v0.13.0.
      Operating System
      macOS
      Additional Context
      No response
      Metadata
      Metadata
      Assignees
      Labels
      bugSomething isn't working
      Type
      No type
      Projects
      No projects
        Milestone
        No milestone
        Relationships
        None yet
        Development
        No branches or pull requests
        Issue actions
        
, 'i');
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var __m = "*";
var __re = new RegExp('^' + ".*" + '
agentcore dev -p <port> is silently offset by runtime index when running multiple runtimes in parallel · Issue #1079 · aws/agentcore-cli · GitHub
        Skip to content
        agentcore dev -p <port> is silently offset by runtime index when running multiple runtimes in parallel #1079
        Closed
        #1661
        Closed
        agentcore dev -p <port> is silently offset by runtime index when running multiple runtimes in parallel#1079
        #1661
        Assignees
        avi-alpert
        Labels
        bugSomething isn't working
        Description
        @masaha03
        masaha03
        opened on May 1, 2026
        Description
        When running multiple agentcore dev instances in parallel, getAgentPort() in
        src/cli/operations/dev/config.ts silently offsets the port passed via
        -p by the runtime's index in agentcore.json (basePort + runtimeIndex). The shift is not logged and the flag's help text ("Port for development server") gives no hint that -p is a base port.
        Why this is a problem
        The actual bound port depends on which other runtimes are configured in agentcore.json and which ones happen to be running, not just on the -p value.
        
This breaks local development and integration testing in practical ways:
        • Downstream services (backend servers, integration tests, scripts) that target http://localhost:<-p value>/invocations silently talk to the wrong port —
          
or get connection errors — depending on which runtimes are up.
        • Which runtime owns which port changes if someone reorders, adds, or removes entries in agentcore.json. A config-only change silently breaks every
          
developer's local setup.
        • To hit a specific port, a user has to compute -p = desiredPort - runtimeIndex and keep that in sync with agentcore.json. The -p value in
          package.json / README / CI scripts no longer means what it says.
        • A second free-port search (findFreePort in src/cli/operations/dev/utils.ts) can shift the port again if basePort + index is occupied, and only
          
that shift is announced. The first, index-based shift is invisible.
        Suggested Fixes (any one resolves the surprise)
        1. Treat -p as the literal port; fail fast on conflict.
        2. Add a per-runtime devPort field in agentcore.json so the mapping is explicit and stable across reorderings.
        3. Log the offset whenever getAgentPort shifts the port, mirroring the existing Port ${ee} in use, using ${re} message.
        4. At minimum, document the current behavior in --help and the README.
        Steps to Reproduce
        1. agentcore.json with two runtimes:

          { "runtimes": [{ "name": "AgentA", ... }, { "name": "AgentB", ... }] }
        2. Run both in parallel with the ports you actually want:

          agentcore dev -r AgentA -p 8787 &
agentcore dev -r AgentB -p 8788 &
        3. lsof -iTCP -sTCP:LISTEN -n -P — AgentB is on 8789, not 8788.
        Expected Behavior
        AgentB binds to 8788 (the value passed via -p).
        Actual Behavior
        AgentB binds to 8789 (8788 + index(AgentB) = 8788 + 1). No log line explains why.
        CLI Version
        @aws/agentcore@0.12.0; logic still on main / v0.13.0.
        Operating System
        macOS
        Additional Context
        No response
        Metadata
        Metadata
        Assignees
        Labels
        bugSomething isn't working
        Type
        No type
        Projects
        No projects
          Milestone
          No milestone
          Relationships
          None yet
          Development
          No branches or pull requests
          Issue actions
          
, 'i');
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})();
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try {
var __m = "youtube.com";
var __re = new RegExp('^' + "youtube\\.com" + '
agentcore dev -p <port> is silently offset by runtime index when running multiple runtimes in parallel · Issue #1079 · aws/agentcore-cli · GitHub
          Skip to content
          agentcore dev -p <port> is silently offset by runtime index when running multiple runtimes in parallel #1079
          Closed
          #1661
          Closed
          agentcore dev -p <port> is silently offset by runtime index when running multiple runtimes in parallel#1079
          #1661
          Assignees
          avi-alpert
          Labels
          bugSomething isn't working
          Description
          @masaha03
          masaha03
          opened on May 1, 2026
          Description
          When running multiple agentcore dev instances in parallel, getAgentPort() in
          src/cli/operations/dev/config.ts silently offsets the port passed via
          -p by the runtime's index in agentcore.json (basePort + runtimeIndex). The shift is not logged and the flag's help text ("Port for development server") gives no hint that -p is a base port.
          Why this is a problem
          The actual bound port depends on which other runtimes are configured in agentcore.json and which ones happen to be running, not just on the -p value.
          
This breaks local development and integration testing in practical ways:
          • Downstream services (backend servers, integration tests, scripts) that target http://localhost:<-p value>/invocations silently talk to the wrong port —
            
or get connection errors — depending on which runtimes are up.
          • Which runtime owns which port changes if someone reorders, adds, or removes entries in agentcore.json. A config-only change silently breaks every
            
developer's local setup.
          • To hit a specific port, a user has to compute -p = desiredPort - runtimeIndex and keep that in sync with agentcore.json. The -p value in
            package.json / README / CI scripts no longer means what it says.
          • A second free-port search (findFreePort in src/cli/operations/dev/utils.ts) can shift the port again if basePort + index is occupied, and only
            
that shift is announced. The first, index-based shift is invisible.
          Suggested Fixes (any one resolves the surprise)
          1. Treat -p as the literal port; fail fast on conflict.
          2. Add a per-runtime devPort field in agentcore.json so the mapping is explicit and stable across reorderings.
          3. Log the offset whenever getAgentPort shifts the port, mirroring the existing Port ${ee} in use, using ${re} message.
          4. At minimum, document the current behavior in --help and the README.
          Steps to Reproduce
          1. agentcore.json with two runtimes:

            { "runtimes": [{ "name": "AgentA", ... }, { "name": "AgentB", ... }] }
          2. Run both in parallel with the ports you actually want:

            agentcore dev -r AgentA -p 8787 &
agentcore dev -r AgentB -p 8788 &
          3. lsof -iTCP -sTCP:LISTEN -n -P — AgentB is on 8789, not 8788.
          Expected Behavior
          AgentB binds to 8788 (the value passed via -p).
          Actual Behavior
          AgentB binds to 8789 (8788 + index(AgentB) = 8788 + 1). No log line explains why.
          CLI Version
          @aws/agentcore@0.12.0; logic still on main / v0.13.0.
          Operating System
          macOS
          Additional Context
          No response
          Metadata
          Metadata
          Assignees
          Labels
          bugSomething isn't working
          Type
          No type
          Projects
          No projects
            Milestone
            No milestone
            Relationships
            None yet
            Development
            No branches or pull requests
            Issue actions
            
, 'i');
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var __m = "*";
var __re = new RegExp('^' + ".*" + '
agentcore dev -p <port> is silently offset by runtime index when running multiple runtimes in parallel · Issue #1079 · aws/agentcore-cli · GitHub
            Skip to content
            agentcore dev -p <port> is silently offset by runtime index when running multiple runtimes in parallel #1079
            Closed
            #1661
            Closed
            agentcore dev -p <port> is silently offset by runtime index when running multiple runtimes in parallel#1079
            #1661
            Assignees
            avi-alpert
            Labels
            bugSomething isn't working
            Description
            @masaha03
            masaha03
            opened on May 1, 2026
            Description
            When running multiple agentcore dev instances in parallel, getAgentPort() in
            src/cli/operations/dev/config.ts silently offsets the port passed via
            -p by the runtime's index in agentcore.json (basePort + runtimeIndex). The shift is not logged and the flag's help text ("Port for development server") gives no hint that -p is a base port.
            Why this is a problem
            The actual bound port depends on which other runtimes are configured in agentcore.json and which ones happen to be running, not just on the -p value.
            
This breaks local development and integration testing in practical ways:
            • Downstream services (backend servers, integration tests, scripts) that target http://localhost:<-p value>/invocations silently talk to the wrong port —
              
or get connection errors — depending on which runtimes are up.
            • Which runtime owns which port changes if someone reorders, adds, or removes entries in agentcore.json. A config-only change silently breaks every
              
developer's local setup.
            • To hit a specific port, a user has to compute -p = desiredPort - runtimeIndex and keep that in sync with agentcore.json. The -p value in
              package.json / README / CI scripts no longer means what it says.
            • A second free-port search (findFreePort in src/cli/operations/dev/utils.ts) can shift the port again if basePort + index is occupied, and only
              
that shift is announced. The first, index-based shift is invisible.
            Suggested Fixes (any one resolves the surprise)
            1. Treat -p as the literal port; fail fast on conflict.
            2. Add a per-runtime devPort field in agentcore.json so the mapping is explicit and stable across reorderings.
            3. Log the offset whenever getAgentPort shifts the port, mirroring the existing Port ${ee} in use, using ${re} message.
            4. At minimum, document the current behavior in --help and the README.
            Steps to Reproduce
            1. agentcore.json with two runtimes:

              { "runtimes": [{ "name": "AgentA", ... }, { "name": "AgentB", ... }] }
            2. Run both in parallel with the ports you actually want:

              agentcore dev -r AgentA -p 8787 &
agentcore dev -r AgentB -p 8788 &
            3. lsof -iTCP -sTCP:LISTEN -n -P — AgentB is on 8789, not 8788.
            Expected Behavior
            AgentB binds to 8788 (the value passed via -p).
            Actual Behavior
            AgentB binds to 8789 (8788 + index(AgentB) = 8788 + 1). No log line explains why.
            CLI Version
            @aws/agentcore@0.12.0; logic still on main / v0.13.0.
            Operating System
            macOS
            Additional Context
            No response
            Metadata
            Metadata
            Assignees
            Labels
            bugSomething isn't working
            Type
            No type
            Projects
            No projects
              Milestone
              No milestone
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agentcore dev -p <port> is silently offset by runtime index when running multiple runtimes in parallel · Issue #1079 · aws/agentcore-cli · GitHub
              Skip to content
              agentcore dev -p <port> is silently offset by runtime index when running multiple runtimes in parallel #1079
              Closed
              #1661
              Closed
              agentcore dev -p <port> is silently offset by runtime index when running multiple runtimes in parallel#1079
              #1661
              Assignees
              avi-alpert
              Labels
              bugSomething isn't working
              Description
              @masaha03
              masaha03
              opened on May 1, 2026
              Description
              When running multiple agentcore dev instances in parallel, getAgentPort() in
              src/cli/operations/dev/config.ts silently offsets the port passed via
              -p by the runtime's index in agentcore.json (basePort + runtimeIndex). The shift is not logged and the flag's help text ("Port for development server") gives no hint that -p is a base port.
              Why this is a problem
              The actual bound port depends on which other runtimes are configured in agentcore.json and which ones happen to be running, not just on the -p value.
              
This breaks local development and integration testing in practical ways:
              • Downstream services (backend servers, integration tests, scripts) that target http://localhost:<-p value>/invocations silently talk to the wrong port —
                
or get connection errors — depending on which runtimes are up.
              • Which runtime owns which port changes if someone reorders, adds, or removes entries in agentcore.json. A config-only change silently breaks every
                
developer's local setup.
              • To hit a specific port, a user has to compute -p = desiredPort - runtimeIndex and keep that in sync with agentcore.json. The -p value in
                package.json / README / CI scripts no longer means what it says.
              • A second free-port search (findFreePort in src/cli/operations/dev/utils.ts) can shift the port again if basePort + index is occupied, and only
                
that shift is announced. The first, index-based shift is invisible.
              Suggested Fixes (any one resolves the surprise)
              1. Treat -p as the literal port; fail fast on conflict.
              2. Add a per-runtime devPort field in agentcore.json so the mapping is explicit and stable across reorderings.
              3. Log the offset whenever getAgentPort shifts the port, mirroring the existing Port ${ee} in use, using ${re} message.
              4. At minimum, document the current behavior in --help and the README.
              Steps to Reproduce
              1. agentcore.json with two runtimes:

                { "runtimes": [{ "name": "AgentA", ... }, { "name": "AgentB", ... }] }
              2. Run both in parallel with the ports you actually want:

                agentcore dev -r AgentA -p 8787 &
agentcore dev -r AgentB -p 8788 &
              3. lsof -iTCP -sTCP:LISTEN -n -P — AgentB is on 8789, not 8788.
              Expected Behavior
              AgentB binds to 8788 (the value passed via -p).
              Actual Behavior
              AgentB binds to 8789 (8788 + index(AgentB) = 8788 + 1). No log line explains why.
              CLI Version
              @aws/agentcore@0.12.0; logic still on main / v0.13.0.
              Operating System
              macOS
              Additional Context
              No response
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agentcore dev -p <port> is silently offset by runtime index when running multiple runtimes in parallel · Issue #1079 · aws/agentcore-cli · GitHub
                Skip to content
                agentcore dev -p <port> is silently offset by runtime index when running multiple runtimes in parallel #1079
                Closed
                #1661
                Closed
                agentcore dev -p <port> is silently offset by runtime index when running multiple runtimes in parallel#1079
                #1661
                Assignees
                avi-alpert
                Labels
                bugSomething isn't working
                Description
                @masaha03
                masaha03
                opened on May 1, 2026
                Description
                When running multiple agentcore dev instances in parallel, getAgentPort() in
                src/cli/operations/dev/config.ts silently offsets the port passed via
                -p by the runtime's index in agentcore.json (basePort + runtimeIndex). The shift is not logged and the flag's help text ("Port for development server") gives no hint that -p is a base port.
                Why this is a problem
                The actual bound port depends on which other runtimes are configured in agentcore.json and which ones happen to be running, not just on the -p value.
                
This breaks local development and integration testing in practical ways:
                • Downstream services (backend servers, integration tests, scripts) that target http://localhost:<-p value>/invocations silently talk to the wrong port —
                  
or get connection errors — depending on which runtimes are up.
                • Which runtime owns which port changes if someone reorders, adds, or removes entries in agentcore.json. A config-only change silently breaks every
                  
developer's local setup.
                • To hit a specific port, a user has to compute -p = desiredPort - runtimeIndex and keep that in sync with agentcore.json. The -p value in
                  package.json / README / CI scripts no longer means what it says.
                • A second free-port search (findFreePort in src/cli/operations/dev/utils.ts) can shift the port again if basePort + index is occupied, and only
                  
that shift is announced. The first, index-based shift is invisible.
                Suggested Fixes (any one resolves the surprise)
                1. Treat -p as the literal port; fail fast on conflict.
                2. Add a per-runtime devPort field in agentcore.json so the mapping is explicit and stable across reorderings.
                3. Log the offset whenever getAgentPort shifts the port, mirroring the existing Port ${ee} in use, using ${re} message.
                4. At minimum, document the current behavior in --help and the README.
                Steps to Reproduce
                1. agentcore.json with two runtimes:

                  { "runtimes": [{ "name": "AgentA", ... }, { "name": "AgentB", ... }] }
                2. Run both in parallel with the ports you actually want:

                  agentcore dev -r AgentA -p 8787 &
agentcore dev -r AgentB -p 8788 &
                3. lsof -iTCP -sTCP:LISTEN -n -P — AgentB is on 8789, not 8788.
                Expected Behavior
                AgentB binds to 8788 (the value passed via -p).
                Actual Behavior
                AgentB binds to 8789 (8788 + index(AgentB) = 8788 + 1). No log line explains why.
                CLI Version
                @aws/agentcore@0.12.0; logic still on main / v0.13.0.
                Operating System
                macOS
                Additional Context
                No response
                Metadata
                Metadata
                Assignees
                Labels
                bugSomething isn't working
                Type
                No type
                Projects
                No projects
                  Milestone
                  No milestone
                  Relationships
                  None yet
                  Development
                  No branches or pull requests
                  Issue actions