[PATCH 1/2] llm: define dtrace skill for debugging workflows

Add llm/SKILL.md as a reusable DTrace skill for agentic coding frameworks that support SKILLs.

Tune the skill for incident response, root-cause analysis, and latency triage.

Require complete runnable scripts and verification before final output to reduce user trial-and-error during investigations.

Signed-off-by: Greg Marsden <[email protected]>
Reviewed-by: Kris Van Hees <[email protected]>
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 llm/SKILL.md | 199 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 199 insertions(+)
 create mode 100644 llm/SKILL.md

diff --git a/llm/SKILL.md b/llm/SKILL.md
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+---
+name: dtrace-linux
+description: Generate and validate runnable DTrace scripts for Linux debugging and performance investigations in an agentic coding framework capable of using SKILLs. Use for incident response, root-cause analysis, latency triage, syscall/process/scheduler/I-O tracing, and stack/profile sampling. Always return complete scripts with safe defaults, stable providers, strict D language constraints, and a verification step before final output.
+---
+
+# DTrace for Linux
+
+Generate complete D scripts that compile and run cleanly on Linux systems with DTrace.
+
+## Output Requirements
+
+- Return a full runnable D program every time.
+- Include a shebang for script output: `#!/usr/sbin/dtrace -s`.
+- Prefer predicates for filtering and aggregations for volume control.
+- Include `dtrace:::ERROR` when the script could fault or when robust diagnostics are useful.
+- Avoid placeholders, pseudo-code, and partial solutions.
+
+## Safety Rules
+
+- Prefer stable providers: `syscall`, `proc`, `sched`, `profile`, `io`, `pid`, `usdt`, and `dtrace`.
+- Avoid dangerous actions unless explicitly necessary.
+- Do not recommend `system()` unless there is no viable alternative.
+- Treat `copyout*()`, `raise()`, and `system()` as destructive.
+
+## Forbidden Language Constructs
+
+Never use these constructs in D scripts:
+
+- `if`
+- `else`
+- `for`
+- `while`
+- `switch`
+- `case`
+- `default`
+- `do`
+- `goto`
+- `continue`
+
+Use only:
+
+- Predicates: `/expr/`
+- Ternary operator: `cond ? a : b`
+
+## Clause Structure
+
+Use this canonical form:
+
+```d
+probe-descriptions
+/ optional predicate /
+{
+    statements;
+}
+```
+
+- Probe description format: `provider:module:function:name`
+- Omitted fields are wildcard matches.
+- Multiple probes may be comma-separated in one clause.
+- Avoid numeric probe IDs.
+
+## Script Skeleton
+
+```d
+#!/usr/sbin/dtrace -s
+
+dtrace:::BEGIN
+{
+    printf("Tracing started...\\n");
+}
+
+/* tracing clauses */
+
+dtrace:::END
+{
+    /* printa() for aggregations when needed */
+}
+
+dtrace:::ERROR
+{
+    printf("DTrace error at %s:%s:%s:%s\\n", probeprov, probemod, probefunc, probename);
+}
+```
+
+## Preferred Idioms
+
+- Filter early with predicates:
+  - `/execname == "date"/`
+  - `/pid == $target/`
+- Use per-thread state for timing:
+  - `self->ts = timestamp;`
+  - `/self->ts/ { @lat = quantize(timestamp - self->ts); self->ts = 0; }`
+- Use aggregations instead of unbounded prints:
+  - `@counts[key] = count();`
+  - `@sum[key] = sum(value);`
+  - `@dist = quantize(value);`
+
+## Variables
+
+- Global: `x`, `arr[key]` (shared, not MP-safe by default)
+- Thread-local: `self->x` (preferred for correlation)
+- Clause-local: `this->x` (temporary per-probe firing)
+- Built-in probe/process vars:
+  - `pid`, `ppid`, `tid`, `execname`
+  - `probeprov`, `probemod`, `probefunc`, `probename`
+  - `timestamp`, `vtimestamp`, `errno`
+  - `arg0` ... `arg9`, `args[]`
+- Macro vars:
+  - `$target`, `$pid`, `$uid`, `$1`, `$2`, ...
+
+## Common Functions
+
+- Recording: `trace()`, `printf()`, `printa()`, `exit()`
+- Aggregation: `count()`, `sum()`, `avg()`, `min()`, `max()`, `stddev()`, `quantize()`, `lquantize()`, `llquantize()`
+- Memory/string: `copyin()`, `copyinstr()`, `strlen()`, `substr()`, `strstr()`
+- Stacks: `stack()`, `ustack()`
+- Speculation: `speculation()`, `speculate()`, `commit()`, `discard()`
+
+## Provider Quick Reference
+
+- `dtrace`: lifecycle (`BEGIN`, `END`, `ERROR`)
+- `syscall`: syscall entry/return
+- `proc`: process lifecycle (`exec`, `exit`, ...)
+- `sched`: scheduler activity (`on-cpu`, `off-cpu`, ...)
+- `profile`: timed sampling (`profile-N`, `tick-N`)
+- `io`: I/O start/complete
+- `pid`: user-function boundaries in a target process
+- `usdt`: user static tracepoints
+
+## Patterns
+
+Count syscalls by executable:
+
+```d
+#!/usr/sbin/dtrace -s
+
+syscall:::entry
+/execname != ""/
+{
+    @syscalls[execname] = count();
+}
+
+dtrace:::END
+{
+    printa(@syscalls);
+}
+```
+
+Time syscall latency:
+
+```d
+#!/usr/sbin/dtrace -s
+
+syscall::write:entry
+{
+    self->ts = timestamp;
+}
+
+syscall::write:return
+/self->ts/
+{
+    @lat[execname] = quantize(timestamp - self->ts);
+    self->ts = 0;
+}
+```
+
+Target one process:
+
+```d
+#!/usr/sbin/dtrace -s
+
+syscall:::entry
+/pid == $target/
+{
+    @calls[probefunc] = count();
+}
+```
+
+## Response Style
+
+- Be precise and production-minded.
+- Prefer compact scripts with clear predicates.
+- Add brief comments only where they prevent ambiguity.
+- After presenting a script, include one short run command when useful:
+  - `sudo dtrace -s script.d`
+
+## Verification Workflow
+
+Always verify generated scripts before presenting them as final.
+
+1. Write the script to a file, for example `script.d`.
+2. Run compile-only verification:
+   - `sudo dtrace -e -s script.d`
+3. If compile-only is unavailable on the target distro, use a short bounded run:
+   - `sudo timeout 3 dtrace -s script.d`
+4. Treat verification failures as blocking:
+   - Fix the script and re-run verification until it passes.
+5. Report verification status with the output:
+   - `Verified: yes` plus the command used.
-- 
2.51.2